Magnetic disk device

Abstract

To provide a magnetic disk device capable of searching for an appropriate read position at high speed.SOLUTION: A magnetic disk device includes a disk, a read head, and a control unit. The control unit includes: a read processing unit that moves the read head to n1 radial positions within a cycle in which the disk rotates m1 times, and executes first read processing for reading data on a track in each radial position; a comparison unit that compares the quality of a plurality of first signals obtained by reading on the first read processing and derives a first signal of the highest quality among the plurality of first signals; and a determination unit that determines the radial position when deriving the first signal of the highest quality among the n1 radial positions as a first appropriate read position, which is suitable for reading the data on the track. Where 1≤m1<n1.SELECTED DRAWING: Figure 20

Description

Technical Field

[0001] Embodiments of the present invention relate to a magnetic disk drive.

Background Art

[0002] As magnetic disk drives, there are known a magnetic disk drive of a Conventional Magnetic Recording (CMR) type (or a conventional recording type) that writes a plurality of tracks at intervals in the radial direction of the disk, a magnetic disk drive of a Shingled Magnetic Recording (SMR, or Shingled Write Recording: SWR) type that overlaps and writes a plurality of tracks in the radial direction of the disk, and a magnetic disk drive of a hybrid recording type that selects and executes the conventional recording type and the shingled recording type.

[0003] A magnetic disk drive has a head including a write head and a read head. The write head and the read head are provided at intervals in the circumferential direction of the disk. As the head seeks to the inner circumferential side of the disk or to the outer circumferential side of the disk, the write head and the read head are likely to be offset in the radial direction. Therefore, the magnetic disk drive can read data of a track by offsetting and arranging the read head at a position offset by a predetermined distance in the radial direction from the position of the read head when a predetermined track is written on the disk by the write head.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] This embodiment provides a magnetic disk drive capable of quickly searching for an appropriate read position.

MEANS FOR SOLVING THE PROBLEMS

[0006] A magnetic disk drive according to an embodiment includes a disk having tracks on a recording layer, a read head for reading data from the recording layer of the disk, a read processing unit that moves the read head to n1 radial positions shifted from each other in the radial direction of the disk within a period in which the disk rotates m1 times, and executes a first read process of reading data of the track at each of the radial positions, a comparison unit that compares the qualities of a plurality of first signals obtained by reading in the first read process, and derives a first signal of the highest quality from among the plurality of first signals, a control unit having a determination unit that determines, as a first appropriate read position appropriate for reading data of the track, the radial position at which the highest-quality first signal is derived among the n1 radial positions, 1 ≦ m1 < n1.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, with reference to the drawings, a magnetic disk device 1 according to a comparative example and each embodiment and a method of searching for an appropriate read position (appropriate read offset correction amount) will be described in detail.

[0009] (Comparative Example) First, the configuration of the magnetic disk device 1 according to the comparative example will be described. FIG. 1 is a block diagram showing the configuration of the magnetic disk device 1 according to the comparative example. In this comparative example, the magnetic disk device 1 is a magnetic disk device of a hybrid recording format. However, the magnetic disk device 1 may be a magnetic disk device of a longitudinal recording format or a magnetic disk device of a normal recording format.

[0010] As shown in FIG. 1, the magnetic disk drive 1 includes a plurality of, for example, 1 to 11 disks (magnetic disks) DK as recording media, a spindle motor (SPM) 20 as a drive motor, a head stack assembly (hereinafter referred to as HSA) 22, a driver IC 120, a head amplifier integrated circuit (hereinafter referred to as head amplifier IC or preamplifier) 130, a volatile memory 70, a buffer memory (buffer) 80, a non-volatile memory 90, and a system controller 110 which is a one-chip integrated circuit. Further, the magnetic disk drive 1 is connected to a host system (hereinafter simply referred to as host) 100.

[0011] Each disk DK is formed, for example, with a diameter of 97 mm (3.8 inches) and has a recording layer (magnetic recording layer) L on both sides thereof. The disk DK has tracks on the recording layer L. The disk DK is attached to the SPM 20 and rotates by the drive of the SPM 20. In this comparative example, the magnetic disk drive 1 includes 1 to 11 disks DK, but the number of disks DK is not limited thereto.

[0012] The arm 30 and the voice coil motor (hereinafter referred to as VCM) 24 constitute an actuator. The actuator can control the movement of the head HD mounted on the arm 30 to a predetermined position of the disk DK by driving the VCM 24, that is, it can seek. As will be described later, the magnetic disk drive 1 includes a plurality of disks DK and a plurality of heads HD.

[0013] For the disk DK, a user data area UU that can be used by the user and a system area SS for writing information necessary for system management are allocated to a writable area of the data. Note that a media cache area (or sometimes referred to as media cache) for temporarily holding data (or commands) transferred from the host 100 or the like before writing to a predetermined area of the user data area UU may be further allocated to the disk DK.

[0014] The head HD records and reproduces information with respect to the disk DK. The head HD has a slider as its main body and includes a write head WHD and a read head RHD mounted on the slider. The arm 30 supports the read head RHD and the write head WHD. The write head WHD writes data to the recording layer L of the disk DK. The read head RHD reads data from the track (data track) of the recording layer L of the disk DK.

[0015] The driver IC 120 controls the driving of the SPM 20 and the VCM 24 in accordance with the control of the system controller 110 (specifically, the MPU 60 described later). The SPM 20 supports and rotates a plurality of disks DK.

[0016] The head amplifier IC 130 includes a read amplifier and a write driver. The read amplifier amplifies the read signal read from the disk DK and outputs it to the system controller 110 (specifically, the read / write (R / W) channel 140 described later). The write driver outputs a write current corresponding to the signal output from the R / W channel 140 to the head HD. Hereinafter, "writing data" may also be referred to as "writing", "data write", "write process", etc. "Reading data" may also be referred to as "reading", "data read", "read process", etc.

[0017] Note that the write head WHD may be simply referred to as the head HD, the read head RHD may be simply referred to as the head HD, or the write head WHD and the read head RHD may be collectively referred to as the head HD. The center (center of gravity) of the head HD may be simply referred to as the head HD, the center (center of gravity) of the write head WHD may be simply referred to as the write head WHD, and the center (center of gravity) of the read head RHD may be simply referred to as the read head RHD.

[0018] In some cases, the "center (center of gravity) of the light head WHD" may simply be referred to as the "head HD", and in some cases, the "center (center of gravity) of the read head RHD" may also be simply referred to as the "head HD". "Positioning the center of the head HD at the track center of a predetermined track" may be expressed as "positioning the head HD on a predetermined track", "placing the head HD on a predetermined track", "positioning the head HD at a predetermined track", etc.

[0019] The volatile memory 70 is a semiconductor memory in which the stored data is lost when the power supply is cut off. The volatile memory 70 stores data and the like necessary for processing in each part of the magnetic disk device 1. The volatile memory 70 is a random access memory (RAM: Random Access Memory). The volatile memory 70 is, for example, a DRAM (Dynamic Random Access Memory). However, the volatile memory 70 may be an SDRAM (Synchronous Dynamic Random Access Memory).

[0020] The buffer memory 80 is a semiconductor memory that temporarily records data and the like transmitted and received between the magnetic disk device 1 and the host 100. Note that the buffer memory 80 may be integrally configured with the volatile memory 70. The buffer memory 80 is a volatile RAM. By way of example, the buffer memory 80 is a DRAM, SRAM (Static Random Access Memory), SDRAM, FeRAM (Ferroelectric Random Access memory), MRAM (Magnetoresistive Random Access Memory), or the like.

[0021] The non-volatile memory 90 is a semiconductor memory that records data stored even when the power supply is cut off. The non-volatile memory 90 is, for example, a NAND-type flash read-only memory (Flash Read Only Memory: FROM). However, the non-volatile memory 90 may also be a NOR-type FROM.

[0022] The system controller (controller) 110 is realized, for example, using a large-scale integrated circuit (LSI) called a System-on-a-Chip (SoC) in which a plurality of elements are integrated on a single chip. The system controller 110 includes a read / write (R / W) channel 140, a hard disk controller (HDC) 150, and a microprocessor (MPU) 60. The system controller 110 is electrically connected to a driver IC 120, a head amplifier IC 130, a volatile memory 70, a buffer memory 80, a non-volatile memory 90, and a host 100.

[0023] The R / W channel 140 executes signal processing of read data transferred from the disk DK to the host 100 and write data transferred from the host 100 in response to an instruction from the MPU 60 described later. The R / W channel 140 includes a write channel 14W and a read channel 14R. The write channel 14W has a circuit or function for modulating write data. The read channel 14R has a circuit or function for measuring the quality of a plurality of signals obtained by reading through a read process. The quality of the above signals is the amplitude of the signal or the bit error rate (BER) of the signal. The R / W channel 140 is electrically connected to, for example, the head amplifier IC 130, the HDC 150, the MPU 60, etc.

[0024] The HDC 150 controls data transfer between the host 100 and the R / W channel 140 in response to an instruction from the MPU 60 described later. The HDC 150 is electrically connected to, for example, the R / W channel 140, the MPU 60, the volatile memory 70, the buffer memory 80, the non-volatile memory 90, etc.

[0025] The MPU60 is a control unit that controls each part of the magnetic disk device 1 and is the main controller. The MPU60 controls the VCM24 via the driver IC120 and executes servo control for positioning the head HD. Also, the MPU60 controls the SPM20 via the driver IC120 to rotate the disk DK. The MPU60 controls the write operation of data to the disk DK and selects the storage destination of the write data transferred from the host 100. Also, the MPU60 controls the read operation of data from the disk DK and controls the processing of the read data transferred from the disk DK to the host 100. The MPU60 is connected to each part of the magnetic disk device 1. The MPU60 is electrically connected to, for example, the driver IC120, the R / W channel 140, the HDC150, etc.

[0026] The MPU60 includes a read / write processing unit 61, a comparison unit 62, a determination unit 63, and a signal quality averaging processing unit 65. The MPU60 executes the processing of these units, for example, the read / write processing unit 61, the comparison unit 62, the determination unit 63, the signal quality averaging processing unit 65, etc. on the firmware. Note that the MPU60 may include these units as circuits.

[0027] The read / write processing unit 61 has a write processing unit 61a and a read processing unit 61b. In accordance with a command from the host 100, the write processing unit 61a controls the write processing of data to the recording layer L of the disk DK, and the read processing unit 61b controls the read processing of data from the recording layer L of the disk DK. The read / write processing unit 61 controls the VCM24 via the driver IC120, positions the head HD at a target position (a predetermined radial position) on the disk DK, and executes read processing or write processing.

[0028] The comparison unit 62 can compare the quality of a plurality of signals obtained by reading in the read process and derive the signal with the highest quality from among the plurality of signals. The determination unit 63 can determine, among a plurality of radial positions on one track of the recording layer L, the radial position at which the highest quality signal is derived as an appropriate lead position that is appropriate for reading the data of the track. The signal quality averaging unit 65 can derive a plurality of averaged qualities. Each averaged quality is a quality obtained by averaging the qualities of a plurality of signals obtained by performing a plurality of reads by the read process at one radial position on the track of the recording layer L.

[0029] FIG. 2 is a perspective view showing a part of the magnetic disk device 1, and shows a plurality of disks DK and a plurality of heads HD. As shown in FIG. 2, in the circumferential direction of the disk DK, the direction in which the disk DK rotates is referred to as the rotation direction d3. In the example shown in FIG. 2, the rotation direction is shown counterclockwise, but it may be in the reverse direction (clockwise). Further, the traveling direction d2 of the head HD with respect to the disk DK is opposite to the rotation direction d3. The traveling direction d2 is the direction in which the head HD sequentially writes and reads data with respect to the disk DK in the circumferential direction, that is, the direction in which the head HD travels with respect to the disk DK in the circumferential direction.

[0030] The magnetic disk device 1 includes i disks DK1 to DKi and j heads HD1 to HDj. In this comparative example, the number of heads HD is twice the number of disks DK (j = 2 × i). The disks DK1 to DKi are provided coaxially and are stacked with a space therebetween. The diameters of the disks DK1 to DKi are the same. Here, terms such as "the same", "identical", "coincident", "equivalent" include not only the meaning of being exactly the same but also the meaning of being different to the extent that they can be regarded as substantially the same. Note that the diameters of the disks DK1 to DKi may be different from each other.

[0031] Each disk DK has recording layers L on both sides. For example, disk DK1 has a first recording layer La1 and a second recording layer Lb1 on the opposite side of the first recording layer La1. Disk DK2 has a first recording layer La2 and a second recording layer Lb2 on the opposite side of the first recording layer La2. Disk DKi has a first recording layer Lai and a second recording layer Lbi on the opposite side of the first recording layer Lai. Each first recording layer La may also be referred to as the surface or the recording surface. Each second recording layer Lb may also be referred to as the back surface or the recording surface.

[0032] Each recording layer L has a user data area UU and a system area SS. The first recording layer La1 has a user data area UUa1 and a system area SSa1. The second recording layer Lb1 has a user data area UUb1 and a system area SSb1. The first recording layer La2 has a user data area UUa2 and a system area SSa2. The second recording layer Lb2 has a user data area UUb2 and a system area SSb2. The first recording layer Lai has a user data area UUai and a system area SSai. The second recording layer Lbi has a user data area UUbi and a system area SSbi.

[0033] Among the user data area UUa1 (first recording layer La1), the track sandwiched by double dashed lines in the figure is defined as track TRa1. Among the user data area UUb1 (second recording layer Lb1), the track located on the opposite side of track TRa1 is defined as track TRb1. Among the user data area UUa2 (first recording layer La2), the track sandwiched by double dashed lines in the figure is defined as track TRc1. Among the user data area UUb2 (second recording layer Lb2), the track located on the opposite side of track TRc1 is defined as track TRd1. Of the user data area UUai (first recording layer Lai), the track sandwiched by double dashed lines in the figure is defined as track TRe1. Of the user data area UUbi (second recording layer Lbi), the track located on the opposite side of track TRe1 is defined as track TRf1. In this comparative example, tracks TaR1, TRb1, TRc1, TRd1, TRe1, and TRf1 are located on the same cylinder.

[0034] Head HD faces the disk DK. In this comparative example, one head HD faces each recording layer L of the disk DK. For example, head HD1 faces the first recording layer La1 of disk DK1, writes data to the first recording layer La1, and reads data from the first recording layer La1. Head HD2 faces the second recording layer Lb1 of disk DK1, writes data to the second recording layer Lb1, and reads data from the second recording layer Lb1.

[0035] Head HD3 faces the first recording layer La2 of disk DK2, writes data to the first recording layer La2, and reads data from the first recording layer La2. Head HD4 faces the second recording layer Lb2 of disk DK2, writes data to the second recording layer Lb2, and reads data from the second recording layer Lb2. Head HDj-1 faces the first recording layer Lai of disk DKi, writes data to the first recording layer Lai, and reads data from the first recording layer Lai. Head HDj faces the second recording layer Lbi of disk DKi, writes data to the second recording layer Lbi, and reads data from the second recording layer Lbi.

[0036] Note that a predetermined position in the radial direction d1 of the disk DK may be referred to as the radial position, and a predetermined position in the circumferential direction of the disk DK may be referred to as the circumferential position. In some cases, the radial position and the circumferential position may be collectively referred to simply as the position. The radial position corresponds to the distance from the rotation center of the disk DK to a predetermined radial position, the distance from the innermost circumference of the disk DK to a predetermined radial position, the distance from the outermost circumference of the disk DK to a predetermined radial position, the distance from a predetermined radial position of the disk DK to another radial position, and the like.

[0037] FIG. 3 is a schematic diagram showing an example of the arrangement of a plurality of servo areas SV and a plurality of data areas DTR on one disk DK according to this comparative example. As shown in FIG. 3, in the radial direction d1 of the disk DK, the direction toward the outer circumference of the disk DK is referred to as the outer direction (outer side), and the direction opposite to the outer direction is referred to as the inner direction (inner side). In FIG. 3, the user data area UU is divided into an inner peripheral area IR located in the inner direction, an outer peripheral area OR located in the outer direction, and a middle peripheral area MR located between the inner peripheral area IR and the outer peripheral area OR.

[0038] The disk DK has a plurality of servo areas SV and a plurality of data areas DTR. The plurality of servo areas SV may be, for example, radially extended in the radial direction of the disk DK and discretely arranged at predetermined intervals in the circumferential direction. The plurality of servo areas SV may be, for example, linearly extended from the inner circumference to the outer circumference and discretely arranged at predetermined intervals in the circumferential direction. The plurality of servo areas SV may be, for example, spirally extended from the inner circumference to the outer circumference and discretely arranged at predetermined intervals in the circumferential direction. Also, the plurality of servo areas SV may be, for example, arranged in an island shape in the radial direction and discretely arranged with different predetermined intervals in the circumferential direction.

[0039] Hereinafter, one servo area SV in a predetermined track may also be referred to as a "servo sector". Note that the "servo area SV" may also be referred to as the "servo sector SV". The servo sector contains servo data. Hereinafter, the "arrangement etc. of some servo data constituting the servo sector" may also be referred to as a "servo pattern". Note that the "servo data written to the servo sector" may also be referred to as the "servo sector".

[0040] A plurality of data areas DTR are respectively arranged between a plurality of servo areas SV. For example, the data area DTR corresponds to the area between two consecutive servo areas SV in the circumferential direction. Hereinafter, one data area DTR on a predetermined track may be referred to as a "data sector". Note that the "data area DTR" may also be referred to as a "data sector DTR". The data sector contains user data. Note that the "user data written in the data sector" may also be referred to as the "data sector". The "data sector" may also be referred to as the "user data". Also, a "pattern composed of several data" may sometimes be referred to as a "data pattern". In the example shown in FIG. 2, the data pattern of a predetermined track is composed of a plurality of servo data (servo sectors) and a plurality of user data (data sectors).

[0041] The servo area SV has a plurality of zone servo areas ZSV and the like. Note that the servo area SV may include, in addition to the zone servo area ZSV, an area including a gap (the circumferential position shift between two zone servo areas), an area including servo data, and a data area DTR and the like. The plurality of zone servo areas ZSV are discretely arranged along the radial direction. The plurality of zone servo areas ZSV each extend in the radial direction.

[0042] One zone servo area (servo area) ZSV on a predetermined track may sometimes be referred to as a "zone servo sector" or a "servo sector". Note that the "zone servo area (servo area) ZSV" may also be referred to as a "zone servo sector ZSV" or a "servo sector ZSV". The "servo data written in the zone servo sector" may sometimes be referred to as the "zone servo sector" or the "servo sector". Hereinafter, the "arrangement etc. of several servo data constituting the zone servo sector" may sometimes be referred to as a "zone servo pattern" or a "servo pattern". Hereinafter, one servo area SV on a predetermined track may sometimes be referred to as a "zone pattern sector".

[0043] Note that the "servo area SV" may also be referred to as a "zone pattern sector". The "at least one piece of data or the like written in the zone pattern sector" may also be referred to as the "zone pattern sector". The zone pattern sector includes at least one zone servo sector. Hereinafter, the "data pattern of the zone pattern sector" may also be referred to as the "zone data pattern".

[0044] In the example shown in FIG. 3, the servo area SV has zone servo areas ZSV0, ZSV1, and ZSV2. The zone servo areas ZSV0, ZSV1, and ZSV2 are arranged in a staggered pattern in the radial direction. The zone servo areas ZSV0, ZSV1, and ZSV2 may be arranged in a stepped pattern in the radial direction.

[0045] The zone servo area ZSV2 is located on the inner circumference side of the zone servo area ZSV1. The zone servo area ZSV0 is located on the outer circumference side of the zone servo area ZSV1. For example, the zone servo area ZSV2 is arranged from the inner circumference area IR to the middle circumference area MR, the zone servo area ZSV1 is arranged from the inner circumference area IR to the outer circumference area OR, and the zone servo area ZSV0 is arranged from the middle circumference area MR to the outer circumference area OR. Hereinafter, in a predetermined servo area SV, a predetermined area in the radial direction where a plurality of zone servo areas ZSV are arranged in the circumferential direction may also be referred to as a zone servo boundary area or a double servo area or a double zone servo area ZB.

[0046] In the example shown in FIG. 3, the main servo area SVO and the sub-servo area SVE are alternately arranged at intervals in the circumferential direction. For example, in the circumferential direction, one sub-servo area SVE is arranged between two main servo areas SVO that are arranged continuously at intervals. For example, when consecutive numbers are assigned to all the servo areas SV of the disk DK in order, the main servo area SVO corresponds to the odd-numbered servo areas SV, and the sub-servo area SVE corresponds to the even-numbered servo areas SV. Note that two or more sub-servo areas SVE may be arranged between two main servo areas SVO that are arranged continuously at intervals in the circumferential direction.

[0047] The main servo area SVO and the sub-servo area SVE may be composed of, for example, only a servo area (hereinafter, may also be referred to as a normal servo area) that reads and demodulates servo data as a whole. Hereinafter, "reading and demodulating servo data" may also be referred to as "servo reading". The main servo area SVO and the sub-servo area SVE may be composed of, for example, a normal servo area and a servo area (hereinafter, may also be referred to as a short servo area) that servo-reads a circumferential range of servo data that is smaller than the circumferential range of the servo data servo-read in the normal servo area.

[0048] A media cache M is allocated to the disk DK. However, the media cache M does not necessarily have to be arranged on the disk DK. By using the plurality of servo data described above, the head HD can be positioned so as to obtain a predetermined off-track amount.

[0049] FIG. 4 is a schematic diagram showing an example of the arrangement of the head HD with respect to the disk DK according to this comparative example. As shown in FIG. 4, track numbers (cylinder numbers) are assigned to concentric tracks (data tracks) formed from the outer circumference OD to the inner circumference ID of the disk DK. If the number of tracks is Nc, the track number C is from 0 to Nc - 1 (C = 0, 1, 2,..., Nc - 1). Each track has a plurality of sectors. Sector numbers are assigned in the advancing direction d2 of the head HD. If the number of sectors is Ns, the sector number S ranges from 0 to Ns - 1 (S = 0, 1, 2, …, Ns - 1).

[0050] By floating on the rotating disk DK, the distance between the head HD and the recording layer L (surface) of the disk DK is maintained within a certain range. The head HD has a write head WHD and a read head RHD. The write head WHD and the read head RHD are arranged in the circumferential direction (Fig. 3). Data on the track written (recorded) by the write head WHD can be read (played back) by the read head RHD.

[0051] Fig. 5 is a diagram showing an example of the geometric arrangement of the head HD with respect to the track when the center of gravity WC of the write head WHD and the center of gravity RC of the read head RHD are arranged in the circumferential direction, when the head HD is opposed to the innermost track, and when the head HD is opposed to the outermost track in this comparative example. Each dashed line in the figure represents the center (track center) of the corresponding track.

[0052] As shown in Fig. 5, in the seek direction, the write head WHD has a width (core width) Ww, and the read head RHD has a width (core width) Wr. The head HD is moved in the seek direction (generally inward or outward) by an actuator and is position-controlled onto the target track. Servo information indicating the radial position on the disk DK is recorded in each sector. By reading the servo information with the read head RHD, the radial position of the head HD on the disk DK can be detected. As will be described later, the seek direction is the first seek direction (e.g., generally inward) or the second seek direction (e.g., generally outward).

[0053] Since the above actuator is generally a rotary actuator, the head HD will have a skew angle with respect to the track depending on the radial position of the head HD on the disk DK. Generally, the write head WHD and the read head RHD are arranged in the rotational direction of the disk DK. For example, when the head HD is positioned on a track where the track number C is Ct, the write head WHD may not be offset either to the outer peripheral side or the inner peripheral side from the read head RHD. When the head HD is positioned on the outer peripheral track of the disk DK, the write head WHD is offset to the outer peripheral side from the read head RHD. Conversely, when the head HD is positioned on the inner peripheral track of the disk DK, the write head WHD is offset to the inner peripheral side from the read head RHD.

[0054] FIG. 6 is a diagram showing the positional relationship between the head HD and the track TRNc-1 which is the innermost peripheral track during the write process and the read process, and the positional relationship between the head HD and the track TR0 which is the outermost peripheral track during the write process and the read process in this comparative example.

[0055] On the left side of FIG. 6, the positional relationship between the head HD and the track TRNc-1 during the write operation and the read operation in the track TRNc-1 where the track number C is Nc-1 is shown. The solid line indicates the position of the head HD during the write operation, and the dashed line indicates the position of the head HD during the read operation.

[0056] When a track TRNc-1 having a track width Wt is formed by the write head WHD, the read head RHD is positioned at a radial position PXw offset by a distance Xs from the write head WHD to the outer peripheral OD side (radial direction d1) by the skew angle. In the direction parallel to the radial direction d1, the distance from the reference position to the read head RHD during the write operation is Xw. Note that the above reference position is, for example, the center (track center) of the track TR0.

[0057] To read the data of track TRNc-1, it is necessary to position the read head RHD at a radial position PXr offset by a distance Xs from the position during the write operation toward the inner circumference ID side. In the direction parallel to the radial direction d1, the distance from the reference position to the read head RHD during the read operation is Xr. In the above case, the distance Xs is the read offset shift amount.

[0058] On the right side of FIG. 6, the positional relationship between the head HD and the track TR0 during the write operation and the read operation in the track TR0 where the track number C is 0 is shown. The head HD indicated by the solid line shows the position during the write operation, and the head HD indicated by the broken line shows the position during the read operation.

[0059] When the track TR0 having the track width Wt is formed by the write head WHD, the read head RHD is positioned at a radial position PXw offset by a distance Xs from the write head WHD toward the inner circumference ID side (the opposite direction of the radial direction d1) due to the skew angle. To read the data of the track TR0, it is necessary to position the read head RHD at a radial position PXr offset by a distance Xs from the position during the write operation toward the outer circumference OD side.

[0060] FIG. 7 is a diagram showing, in this comparative example, the change in the position of the read head RHD in a plurality of tracks TR in a graph. On the horizontal axis of FIG. 7, the right direction corresponds to the inner direction of the disk DK, and the left direction corresponds to the outer direction of the disk DK. On the vertical axis of FIG. 7, the upward direction corresponds to the inner direction of the disk DK, and the downward direction corresponds to the outer direction of the disk DK.

[0061] As shown in FIG. 7, the solid line represents the radial position PXw of the read head RHD during the write process, and the broken line represents the radial position PXr of the read head RHD during the read process. It can be seen that the positional relationship between the radial position PXw of the read head RHD during the write process and the radial position PXr of the read head RHD during the read process is reversed between the inner circumference ID side and the outer circumference OD side.

[0062] FIG. 8 is a diagram showing, in this comparative example, changes in the lead-off offset shift amount Xs in a plurality of tracks TR in a graph. On the horizontal axis of FIG. 8, the right direction corresponds to the inner direction of the disk DK, and the left direction corresponds to the outer direction of the disk DK. On the vertical axis of FIG. 8, the upward direction corresponds to the inner direction of the disk DK, and the downward direction corresponds to the outer direction of the disk DK.

[0063] As shown in FIG. 8, the lead-off offset shift amount Xs can be obtained from the difference between the distance Xr and the distance Xw (Xs = Xr - Xw). In this comparative example, the lead-off offset shift amount Xs is calculated by the MPU 60 (for example, the read processing unit 61b). However, it is not necessary to obtain the lead-off offset shift amount Xs by calculation. In that case, a memory such as the non-volatile memory 90 may have a table having information on the lead-off offset shift amount Xs.

[0064] In this way, by positioning the read head RHD at the radius position PXr offset by the lead-off offset shift amount Xs from the radius position PXw at the time of writing according to the skew angle, reading can be performed at the center position of the track TR.

[0065] By the way, the positional relationship between the write head WHD and the read head RHD in the head HD, particularly their positional relationship in the seek direction, has individual differences and thus does not always match between individuals. For example, there may be an offset between the write head WHD and the read head RHD due to some cause including manufacturing variations. Also, the magnetic field distribution generated by the write head WHD is biased in the radial direction d1 of the disk DK due to the skew angle and individual differences described above. Therefore, it often happens that the center position of the track width Wt of the track TR does not become an appropriate read position for reading the data of the track TR. Therefore, in addition to the lead-off offset shift amount Xs with respect to the radius position of the target track caused by the skew angle as described above, it is necessary to obtain an appropriate value Xcopt (for example, an optimum value) of the lead-off offset correction amount Xc for correcting this.

[0066] FIG. 9 is a diagram showing the positional relationship between the track TR (track TRCt) and the head HD in three cases where the lead offset correction amounts Xc are different from each other in this comparative example. Note that the lead offset shift amount Xs with respect to the target track due to the skew angle as described above is assumed to be zero and is not shown.

[0067] As shown in FIG. 9, when the write head RHD is positioned at the radius position PXw during writing and the writing process is executed, the write head WHD forms a track TR having a track width Wt substantially equal to the width Ww. At this time, due to the deviation in the radial direction d1 of the write head WHD and the read head RHD described above, when the read head RHD is positioned at the appropriate read position PXropt offset by the appropriate lead offset correction amount Xcopt from the radius position PXw, an appropriate read operation can be performed. To obtain the appropriate lead offset correction amount Xcopt, a read operation is performed at the radius positions PXr[i] to which several lead offset correction amounts Xc[i] are applied, and the radius position at which an appropriate (good) read state is obtained is determined. When the read operation of the track TR is performed at k points, the read operation can be performed at k radius positions PXr[0], PXr[1], PXr[2],..., PXr[k-1].

[0068] FIG. 10 is a diagram graphically showing the change in the amplitude of the read signal with respect to the radius position of the read head RHD in this comparative example. As shown in FIG. 10, the profile of the amplitude AP[i] of the signal when reading data on the track TR is graphically represented at the radius positions PXr[i] for each of the k lead offset correction amounts Xc[i] (lead offset correction amounts Xc[0], Xc[1], Xc[2],..., Xc[k-1]). Here, the lead offset correction amount Xc[i] at which the amplitude AP[i] of the signal read by the read head RHD becomes maximum can be obtained and used as the appropriate lead offset correction amount Xcopt.

[0069] In the example of FIG. 10, the highest quality signal is the signal with the maximum amplitude AP[i] among the plurality of signals. Desirably, the highest quality signal is the signal with the maximum amplitude AP[i] among the plurality of signals.

[0070] FIG. 11 is a diagram showing a graph of the change in the bit error rate (BER) of the read signal with respect to the radial position of the read head RHD in this comparative example. As shown in FIG. 11, instead of the amplitude of the read signal, the bit error rate of the read signal may be measured. At the radial position PXr[i] for each of the k-point read offset correction amounts Xc[i], the profile of the bit error rate ER[i] of the signal when reading the data on the track TR is represented by a graph. Here, the read offset correction amount Xc[i] at which the bit error rate ER[i] of the signal read by the read head RHD is minimized can be obtained and used as the appropriate read offset correction amount Xcopt.

[0071] In the example of FIG. 11, the highest quality signal is the signal with the minimum bit error rate ER[i] among the plurality of signals. Desirably, the highest quality signal is the signal with the minimum bit error rate ER[i] among the plurality of signals.

[0072] In the method for searching for the track center in this comparative example, first, data for one round is written to the target track TR. Then, by fixing the read head RHD at a predetermined radial position and reading the data on the track TR for one round, the read channel 14R measures a plurality of bit error rates related to the signal, and the signal quality averaging unit 65 derives an averaged bit error rate obtained by averaging the plurality of bit error rates. Also in the subsequent search method, the averaged bit error rate is derived while changing the radial position at which the read head RHD is fixed.

[0073] Thereafter, the comparison unit 62 derives the minimum averaged bit error rate from among the plurality of averaged bit error rates, and the determination unit 63 determines the radius position at which the minimum averaged bit error rate is derived as the appropriate lead position.

[0074] FIG. 12 is a block diagram showing an example of the positioning control system SY of the head HD according to this comparative example. As shown in FIG. 12, the magnetic disk device 1 has a positioning control system SY for the head HD. The positioning control system SY includes a transducer (Transducer: Physical target Transducer For Writing) TD, a generator (Generator: Read Offset Generator) ROG1, a generator (Generator: Read Offset Generator) ROG2, an adder AD1, an adder AD2, a subtractor SU1, a controller (Controller) CL, and an actuator P.

[0075] The transducer TD, the generator ROG1, the generator ROG2, the adder AD1, the adder AD2, the subtractor SU1, and the controller CL are included in, for example, the head amplifier IC130, the system controller 110, etc. The actuator P is composed of, for example, an arm 30, a VCM 24, etc. The subtractor SU1, the controller CL, and the actuator P constitute a feedback system.

[0076] The magnetic disk device 1 is instructed of the address (C, H, S) of the sector of the read target from the host 100. Here, regarding the sector of the read target, C is the track number (cylinder number), H is the head number, and S is the sector number. Then, the transducer TD converts the above address into a distance Xw corresponding to the track number C and outputs it. The generator ROG1 converts the above address into a read offset shift amount Xs caused by the skew angle (or, the track number C, the radius position, etc.) and outputs it. The generator ROG2 converts the above address into a read offset correction amount Xc due to factors other than the skew angle and outputs it.

[0077] As described above with reference to FIGS. 10 and 11, etc., the lead offset correction amount Xc can be obtained by measuring the lead offset profile of the signal led in the pre-shipment test process or the like, and an appropriate lead offset correction amount Xcopt or the like can be derived. Information on the lead offset shift amount Xs and the lead offset correction amount Xc is input to the adder AD1, and the adder AD1 outputs information (Xs + Xc) obtained by adding the lead offset correction amount Xc to the lead offset shift amount Xs to the adder AD2. The adder AD2 outputs information on the distance Xr (Xr = Xw + Xs + Xc) obtained by adding information (Xs + Xc) obtained by adding the lead offset correction amount Xc to the lead offset shift amount Xs to the distance Xw to the subtractor SU1.

[0078] To measure the lead offset profile, it can be realized by leading the data of the track TR once while changing the lead offset correction amount Xc to each of k lead offset correction amounts Xc[0], Xc[1], Xc[2],..., Xc[k - 1], and measuring the quality (amplitude or bit error rate) of the led signal. The radius position PXr, which is the lead target position at this time, can be determined by the information on the distance Xr.

[0079] The physical radius position Yr of the lead head RHD can be obtained by reading and demodulating the servo information on the disk DK. The subtractor SU1 outputs the positioning error e, which is information obtained by subtracting the physical radius position Yr from the distance Xr, to the controller CL (e = Xr - Yr). In order to realize stable positioning control in the controller CL, the controller CL can obtain the control amount U by performing gain compensation and phase compensation on the positioning error e. Then, by driving the actuator P with the control amount U as an input, the lead head RHD can be position-controlled to the lead target position (radius position PXr).

[0080] FIG. 13 is a diagram for explaining the movement of the head HD when reading the data of the track TRCt while changing the lead offset correction amount Xc in this comparative example. FIG. 13 shows (a) a state where the read head RHD is fixed at the first radial position and reading the data of the track TRCt, (b) a state where the read head RHD is being moved to the second radial position, (c) a state where the read head RHD is fixed at the first radial position and reading the data of the track TRCt from the first radial position to the second radial position, (d) a state where the read head RHD is being moved from the second radial position to the third radial position, and (e) a state where the read head RHD is fixed at the last radial position and reading the data of the track TRCt.

[0081] As shown in FIG. 13, the position and movement of the read head RHD on the disk DK when measuring the amplitude or bit error rate of the read signal can be understood. In the radial direction d1, FIG. 13 shows three tracks TR, namely the track TRCt, and the tracks TRCt-1 and TRCt+1 before and after the track TRCt. In the circumferential direction, FIG. 13 shows five sectors SCNs-2, SCNs-1, SC0, SC1, SC2 having sector numbers S of 0 and sector numbers S before and after the sector number S of 0, which are Ns-2, Ns-1, 1, 2.

[0082] In the track TRCt, by changing the lead offset correction amount Xc[i] while sequentially changing the variable i to 0, 1, 2,..., k-1, the read head RHD moves sequentially to a plurality of radial positions PXr[i]. The radial positions PXr[i] are indicated by concentric dotted lines.

[0083] As shown in FIG. 13(a), first, the variable i is set to 0, the lead offset correction amount is fixed to Xc[0], and the read process is started from the sector SC0 of the track TRCt. As indicated by the solid arrow, the read process is performed in sequence on the sectors SC0, SC1, and SC2, and the read process is performed up to the sector SCNs-1, and the read process for reading one round of the data of the track TRCt is terminated. The radial position PXrs, which is the radial position PXr for initially positioning the read head RHD, is a position that is at a distance Xr[0] from the reference position (Xr[0] = Xw + Xs + Xc[0]).

[0084] As shown in FIG. 13(b), subsequently, when starting the read process at the radial position PXr[1], as indicated by the dashed arrow, since an offset seek operation from the radial position PXr[0] to the radial position PXr[1] needs to be performed, the read process is not immediately carried out, and a seek operation and a standby operation (rotation waiting operation) are performed. Note that the dashed arrow represents both the seek operation and the standby operation. Here, the disk DK rotates once during the seek operation and the standby operation.

[0085] As shown in FIG. 13(c), thereafter, the read head RHD is fixed at the radial position PXr[1] as indicated by the solid arrow from the sector SC0 of the track TRCt, and the read process is resumed.

[0086] Thereafter, until the variable i reaches k - 1, the read process, the seek operation, and the standby operation are repeatedly performed. After performing the read process with the read head RHD fixed at the radial position PXr[k - 1], the reading of the data on the track TRCt is completed. The radial position PXre, which is the radial position PXr for finally positioning the read head RHD, is a position that is at a distance Xr[k - 1] from the reference position (Xr[k - 1] = Xw + Xs + Xc[k - 1]). By the above-described various operations, a more accurate profile of the amplitude of the signal or a more accurate profile of the bit error rate of the signal at a plurality of radial positions PXr[i], which are also a plurality of read positions, can be obtained.

[0087] FIG. 14 is a diagram showing, in a graph, the change in bit error rate ER[i], the change in read offset correction amount Xc[i], and the change in the sector number S of the target position, when the read process, seek operation, and standby operation are repeatedly performed on the target track TR in this comparative example. From the topmost row, the operation mode, the bit error rate ER of the measured signal, the read offset correction amount Xc, and the sector number S are represented.

[0088] As shown in FIG. 14, with the read offset correction amount set to Xc[0], during the period Trot in which the disk DK makes one rotation, the read channel 14R measures the bit error rate of the signal read from the data of sector SC0 to the data of sector SCNs-1 of the track TR.

[0089] The signal quality averaging processing unit 65 averages a plurality of bit error rates ER[0] obtained while the read offset correction amount is set to Xc[0], and derives an averaged bit error rate. Subsequently, by changing the read offset correction amount from Xc[0] to Xc[1], a seek operation (offset seek) and a standby operation are performed. During the standby operation, the read channel 14R and the like are in an idle state.

[0090] In the subsequent read process, the read offset correction amount is fixed to Xc[1], and during the period Trot in which the disk DK makes one rotation, the read channel 14R measures the bit error rate of the signal read from the data of sector SC0 to the data of sector SCNs-1 of the track TR. The signal quality averaging processing unit 65 averages a plurality of bit error rates ER[1] obtained while the read offset correction amount is set to Xc[1], and derives an averaged bit error rate. Thereafter, until the variable i reaches k-1, by repeatedly performing the read process, seek operation, and standby operation on the target track TR, the acquisition of a plurality of averaged bit error rates is completed.

[0091] However, in the track center search method as shown in FIG. 14, in order to obtain the profiles of the bit error rates at a plurality of radius positions PXr[i], a time period of 2×k×Trot is required. For example, in the magnetic disk device 1 with a rotational speed of 7200 rpm, the period Trot is 8.3 msec (Trot = 8.3 msec). Also, let k = 10. Then, to perform the read process at 10 radius positions PXr and obtain the profile of the bit error rate, a time period of 166 msec is required (2×k×Trot = 2×10×8.3 [msec]).

[0092] According to the magnetic disk device 1 configured as described above and the method for searching for the appropriate read position PXropt, for example, if the time period for searching for the track center increases during the manufacturing process, the total time required for adjusting the magnetic disk device 1 during manufacturing increases, which may lead to an increase in manufacturing costs. In particular, in the magnetic disk device 1 with the shingled recording format, the radius position PXr with respect to the radius position PXw changes significantly depending on the track pitch. Since the process of obtaining the appropriate read offset correction amount Xcopt (track center search) is essential, the influence of the time period for obtaining the appropriate read offset correction amount Xcopt on the manufacturing period is significant. There may be a case where the track center is searched not only before the magnetic disk device 1 is actually used but also after the magnetic disk device 1 is actually used. Also in that case, it is desirable that the time period required for searching for the track center is short.

[0093] (First Embodiment) Next, the configuration of the magnetic disk device 1 according to the first embodiment will be described. FIG. 15 is a block diagram showing the configuration of the magnetic disk device 1 according to the first embodiment. The magnetic disk device 1 is configured in the same manner as the magnetic disk device 1 of the above comparative example except for the configuration described in this first embodiment.

[0094] As shown in FIG. 15, the MPU 60 further includes a read position averaging processing unit 64. The configuration and function of the read position averaging processing unit 64 will be described later. During the period when the disk DK rotates m1 times, the read processing unit 61b can move the read head RHD to n1 radial positions PXr that are shifted from each other in the radial direction d1 of the disk DK, and execute a first read process of reading the data of the track TR at each radial position PXr.

[0095] The read channel 14R can measure the quality of a plurality of first signals obtained by the read in the first read process. Note that the quality of the first signal is the amplitude or bit error rate described above. The comparison unit 62 can compare the quality of a plurality of first signals obtained by the read in the first read process, and derive the first signal with the highest quality from among the plurality of first signals. The determination unit 63 can determine the radial position PXr (PXropt1) at which the first signal with the highest quality is derived among the n1 radial positions PXr as the first appropriate read position PXropt1 that is appropriate for reading the data of the track TR.

[0096] In the present first embodiment, the magnetic disk device 1 satisfies the relationship of the following formula 1. 1≦m1<n1 … Formula 1 For example, the value m1 is 1 (m1 = 1). The value n1 corresponds to the value k and is, for example, 10 (n1 = 10). Since m1≧n1 is not satisfied, the first appropriate read position PXropt1 can be searched for at high speed. In other words, the time period for obtaining the first appropriate read offset correction amount Xcopt1 (searching for the track center) can be shortened compared to the above comparative example.

[0097] When reading the data of the track TR, the read processing unit 61b can move the read head RHD to the first appropriate read position PXropt1, and thereby read the data of the track TR at the first appropriate read position PXropt1.

[0098] The write processing unit 61a can move the read head RHD to the standby position which is the radial position PXw, and execute a write process of writing data to the track TR with the write head WHD.

[0099] The first appropriate read position PXropt1 is a position offset from the standby position (radial position PXw), and when reading the data of the track TR, the read processing unit 61b moves the read head RHD to the first appropriate read position PXropt1 offset from the standby position, and can read the data of the track TR at the first appropriate read position PXropt1.

[0100] On the other hand, when the first appropriate read position PXropt1 coincides with the standby position (radial position PXw) and reading the data of the track TR, the read processing unit 61b moves the read head RHD to the first appropriate read position PXropt1 which is the standby position, and can read the data of the track TR at the first appropriate read position PXropt1. As described above, when reading the data of the track TR, offset correction may be performed as necessary from the time of writing to the track TR.

[0101] FIG. 16 is a diagram for explaining the movement of the head HD when reading the data of the track TRCt while changing the read offset correction amount Xc[i] in the first embodiment, and shows a state in which the data of the track TRCt is being read while moving the read head RHD from the initial radial position PXrs to the final radial position PXre. As shown in FIG. 16, the position and movement of the read head RHD on the disk DK when measuring the amplitude or bit error rate of the read signal can be understood. In the radial direction d1, three tracks TRCt-1, TRCt, TRCt+1 are shown in FIG. 16 in the same manner as FIG. 13. In the circumferential direction, five sectors SCNs-2, SCNs-1, SC0, SC1, SC2 are shown in FIG. 16 in the same manner as FIG. 13.

[0102] In track TRCt, by changing the variable i in sequence as 0, 1, 2, …, k - 1 and changing the read offset correction amount Xc[i], the read head RHD moves sequentially to a plurality of radial positions PXr[i]. The radial positions PXr[i] are indicated by concentric dashed lines.

[0103] First, set the variable i to 0, set the read offset correction amount to Xc[0], and start the read process from sector SC0 of track TRCt. Subsequently, as indicated by the solid arrow, perform the read process sequentially while gradually increasing the read offset correction amount Xc at a constant ratio as the sector number S increases, set the read offset correction amount Xc to Xce (Xc[k - 1]), and perform the read process on the final sector SCNs - 1. By performing the read process in this way, it is possible to measure the quality (e.g., bit error rate) of signals in the range from the radial position PXrs to the radial position PXre during one rotation of the disk DK.

[0104] For example, when the number of sectors SC (the above value k) of track TRCt is 500, the quality of the signal can be measured at 500 points within the range from the radial position PXrs to the radial position PXre. Also, in the operation example of FIG. 16, the magnetic disk device 1 satisfies the relationship of the above-described formula (1 ≦ m1 < n1).

[0105] Note that the timing for setting the read offset correction amount Xc to Xce (Xc[k - 1]) is not limited to the timing of performing the read process on sector SCNs - 1 and can be variously deformed. For example, the timing for setting the read offset correction amount Xc to Xce (Xc[k - 1]) may be the timing of performing the read process on sector SCNs - 4.

[0106] Also, the read channel 14R does not necessarily need to measure the quality of the signal read for each sector SC. For example, the read channel 14R may measure the quality of the signal read every several sectors SC.

[0107] FIG. 17 is a diagram showing, in the first embodiment, changes in the bit error rate ER[i], changes in the read offset correction amount Xc[i], and changes in the sector number S of the target position, respectively, in a graph when a read process is performed on the target track TRCt. FIG. 17 corresponds to FIG. 14 of the comparative example.

[0108] As shown in FIG. 17, as the read process is performed while shifting the target sector SC in the advancing direction d2 with respect to the sectors SC0, SC1, and SC2, the radial position PXr[i] changes from the radial position PXrs to the radial position PXre. Therefore, it is possible to acquire a profile of the quality (bit error rate) of the read signal during the period Trot in which the disk DK makes one rotation.

[0109] FIG. 18 is a block diagram showing an example of the positioning control system SY of the head HD according to the first embodiment. As shown in FIG. 18, the positioning control system SY includes a generator (Generator: Read Offset Generator) ROG3 instead of the generator ROG2. Information on the sector number S of the read target sector SC is input to the generator ROG3. The generator ROG3 converts and outputs it to the read offset correction amount Xc based on the sector number S.

[0110] For example, the read offset correction amount Xc depends only on the sector number S. In that case, the read offset correction amount Xc for the sector SC0 of the track TR0 and the read offset correction amount Xc for the sector SC0 of the track TRNc-1 are the same.

[0111] FIG. 19 is a diagram showing, in the first embodiment, the change in the lead-off offset correction amount Xc with respect to the position (radial position) of the target sector SC in a graph, and is a diagram showing an example in which the lead-off offset correction amount Xc is changed along a linear trajectory. The lead-off offset correction amount Xc in FIG. 19 can be obtained by calculation. However, it is not necessary to obtain the lead-off offset correction amount Xc by calculation. In that case, a memory such as the nonvolatile memory 90 may have a table having information on the lead-off offset correction amount Xc.

[0112] As shown in FIG. 19, when executing the first lead process, the lead processing unit 61b seeks the lead head RHD at a constant speed in the first seek direction (in this example, generally the inward direction). The n1 radial positions PXr are provided at equal intervals in the radial direction d1. When executing the first lead process, the lead processing unit 61b can read the data of the track TR at regular time intervals.

[0113] During the period in which the disk DK makes one rotation, the lead-off offset correction amount Xc changes (increases) linearly. The lead-off offset correction amount Xc when reading the data of the sector SC0 is Xcs (Xc[0]), and the lead-off offset correction amount Xc when reading the data of the sector SCNs-1 is Xce (Xc[k - 1]).

[0114] From the bit error rate profile of the signal obtained by reading the data of one round of the track TR, it is possible to obtain the sector number S which is Sopt1 when the bit error rate is minimized and the first appropriate lead-off offset correction amount Xcopt1 which is the lead-off offset correction amount Xc. However, it is desirable that the sector number Sopt1 and the first appropriate lead-off offset correction amount Xcopt1 be the values when the bit error rate is at a minimum.

[0115] FIG. 20 is a flowchart for explaining a method of searching for the first appropriate lead-off offset correction amount Xcopt1 applicable to the magnetic disk device 1 of the first embodiment. As shown in FIG. 20, when a method for searching for a first appropriate lead-off offset correction amount Xcopt1 for the track TR is started, first, in step STa1, the lead processing unit 61b initializes the sector number S of the target position to 0 (S = 0).

[0116] Subsequently, in step STa2, according to the lead-off offset correction amount Xc(S) obtained from the generator ROG3, the lead processing unit 61b moves and positions the read head RHD at the radial position PXr(S) within the first range. Then, in step STa3, the read channel 14R measures the bit error rate ER(S). The radial position PXr(S) is a position separated from the reference position by a distance Xr(S) (Xr(S)=Xw + Xs + Xc(S)). The first range is a range having a width in the radial direction d1, which is a range from the radial position PXrs to the radial position PXre.

[0117] Thereafter, in step STa4, the lead processing unit 61b increments the sector number S of the target position. Subsequently, in step STa5, the lead processing unit 61b determines whether the sector number S of the target position has exceeded the final sector number Ns - 1. If the sector number S has not exceeded the sector number Ns - 1 (S ≤ Ns - 1), the process proceeds to step STa2, and the processes of steps STa2 to STa5 are repeatedly executed.

[0118] On the other hand, in step STa5, when it is determined that the sector number S of the target position has exceeded the sector number Ns - 1 (S = Ns), the measurement of the bit error rate ER within the first range has ended, and the process proceeds to step STa6. In step STa6, the comparison unit 62 compares the bit error rates ER of a plurality of first signals obtained by reading in the first lead process, and derives a first signal with the minimum (preferably minimum) bit error rate ER from among the plurality of first signals. Then, it is possible to search for Smin, which is the sector number S when the first signal with the minimum bit error rate ER is derived.

[0119] Next, in step STa7, the determination unit 63 determines that the read offset correction amount Xc[Smin] when reading the sector SCmin having the sector number S of Smin is the first appropriate read offset correction amount Xcopt1 (Xcopt1 = Xc[Smin]). Thereby, the method for searching for the first appropriate read offset correction amount Xcopt1 for the track TR ends.

[0120] According to the magnetic disk device 1 according to the first embodiment configured as described above and the method for searching for the first appropriate read position PXropt1, the magnetic disk device 1 includes a disk DK having a track TR on the recording layer L, a read head RHD, and an MPU 60. The MPU 60 includes a read processing unit 61b, a comparison unit 62, and a determination unit 63.

[0121] The read processing unit 61b can execute a first read process of moving the read head RHD to n1 radial positions PXr shifted from each other in the radial direction d1 of the disk DK within a period in which the disk DK rotates m1 times, and reading the data of the track TR at each radial position PXr. The comparison unit 62 can compare the qualities of a plurality of first signals obtained by the read in the first read process, and derive the first signal with the highest quality from among the plurality of first signals. The determination unit 63 can determine that the radial position PXr (PXropt1) when the first signal with the highest quality is derived among the n1 radial positions PXr is the first appropriate read position PXropt1 appropriate for reading the data of the track TR.

[0122] 1 ≦ m1 < n1. Therefore, in the first embodiment, the first appropriate read position PXropt1 can be searched for at high speed, and the time period for obtaining the first appropriate read offset correction amount Xcopt1 (searching for the track center) can be shortened.

[0123] (Modification Example 1 of the First Embodiment) Next, the configuration of the magnetic disk drive 1 according to Modification 1 of the first embodiment will be described. FIG. 21 is a diagram showing changes in the lead-off offset correction amount Xc with respect to the position (radial position) of the target sector SC in three types of graphs in this Modification 1, and shows an example in which the lead start position is shifted three times in the circumferential direction, and the lead-off offset correction amount Xc is changed along the same straight line trajectory. FIG. 22 is a diagram showing, in this Modification 1, the changes in the bit error rate ER, the changes in the lead-off offset correction amount Xc, and the changes in the sector number of the target position, respectively, when the read process, the seek operation, and the standby operation are repeatedly performed on the target track TR, each shown in a graph.

[0124] The magnetic disk drive 1 is configured in the same manner as the magnetic disk drive 1 of the first embodiment except for the configuration described in this Modification 1. In this Modification 1, the appropriate read position PXropt can be searched for at high speed, and the sector dependence of the bit error rate can be averaged.

[0125] As shown in FIGS. 21 and 22, the read processing unit 61b performs the first read process in the same manner as in the first embodiment (FIG. 19). In the first read process, the read processing unit 61b first reads the data of the sector SC0 with the lead-off offset correction amount Xc being Xcs (Xc[0]), and finally reads the data of the sector SCNs-1 with the lead-off offset correction amount Xc being Xce (Xc[k-1]).

[0126] From the profile of the bit error rate of the signal obtained by reading one round of the data on the track TR, the sector number S at which the bit error rate is minimized, Sopt1, and the first appropriate lead-off offset correction amount Xcopt1 which is the lead-off offset correction amount Xc can be obtained.

[0127] The read processing unit 61b sequentially executes a seek operation, a rotation wait operation, and a second read processing following the first read processing. The second read processing seeks the read head RHD in the first seek direction within the period during which the disk DK rotates m2 times, moves the read head RHD to n2 radial positions PXr shifted from each other in the radial direction d1, and reads the data of the track TR at each radial position PXr.

[0128] In the first modification example 1, the magnetic disk device 1 satisfies the following relationship of Expression 2. 1 ≦ m2 < n2 … Expression 2 The operation of seeking the read head RHD during the second read processing is the same as the operation of seeking the read head RHD during the first read processing. In the first modification example 1, n1 = n2 and m1 = m2. In the second read processing, the read processing unit 61b first reads the data of the sector SC{(2 / 3)(Ns - 1)} with the read offset correction amount Xc as Xcs(Xc[0]), and finally reads the data of the sector SC{(2 / 3)(Ns - 1) - 1} with the read offset correction amount Xc as Xce(Xc[k - 1]).

[0129] The position (sector SC0) where the data of the track TR is first read in the first read processing and the position (sector SC{(2 / 3)(Ns - 1)}) where the data of the track TR is first read in the second read processing are shifted from each other in the circumferential direction. As described above, it can be seen that in each of the first read processing and the second read processing, the read offset correction amount Xc is changed on the same linear track.

[0130] The comparison unit 62 can further compare the qualities of a plurality of second signals obtained by the read in the second read processing and derive the second signal with the highest quality from among the plurality of second signals. The determination unit 63 can further determine the radial position PXropt2a, which is appropriate for reading the data of the track TR, as the radial position PXr when the second signal with the highest quality is derived among the n2 radial positions PXr.

[0131] For example, from the profile of the bit error rate of the signal obtained by reading one round of the data of track TR in the second read process, the sector number S when the bit error rate is minimized, i.e., Sopt2a, and the second appropriate read offset correction amount Xcopt2a which is the read offset correction amount Xc can be obtained.

[0132] The read position averaging processing unit 64 can derive an averaging position which is the position obtained by averaging the first appropriate read position PXropt1 and the second appropriate read position PXropt2a in the radial direction d1. Thereby, when reading the data of track TR, the read processing unit 61b can move the read head RHD to the above averaging position and read the data of track TR at the above averaging position. It becomes easier to perform the read processing by positioning the read head RHD at a more appropriate radial position PXr than in the above first embodiment, and it becomes easier to obtain a higher quality signal by the read processing.

[0133] The number of times of read processing for one track is not limited to 2 times and may be performed 3 times or more. In this modification example 1, the read processing including the above first read processing and the above second read processing is performed 3 times. The read processing unit 61b sequentially executes a seek operation, a rotation waiting operation, and a third read processing following the second read processing. In the third read processing, within the period when the disk DK rotates m times (for example, m2 times), the read head RHD is seeked in the first seek direction in the same manner as in the second read processing, the read head RHD is moved to n (for example, n2) radial positions PXr shifted from each other in the radial direction d1, and the data of track TR is read at each radial position PXr (1 ≦ m < n).

[0134] The operation of seeking the read head RHD during the third read processing is the same as the operation of seeking the read head RHD during the first read processing and the second read processing. In the third read process, the read processing unit 61b first reads the data of the sector SC{(1 / 3)(Ns - 1)} with the read offset correction amount Xc as Xcs(Xc[0]), and finally reads the data of the sector SC{(1 / 3)(Ns - 1)-1} with the read offset correction amount Xc as Xce(Xc[k - 1]).

[0135] The position (sector SC0) where the data of the track TR is first read in the first read process, the position (sector SC{(2 / 3)(Ns - 1)}) where the data of the track TR is first read in the second read process, and the position (sector SC{(1 / 3)(Ns - 1)}) where the data of the track TR is first read in the third read process are shifted from each other in the circumferential direction. As described above, it can be seen that in each of the first read process, the second read process, and the third read process, the read offset correction amount Xc is changed on the same straight track.

[0136] The comparison unit 62 can further compare the qualities of a plurality of third signals obtained by the read in the third read process, and derive the third signal with the highest quality from among the plurality of third signals. The determination unit 63 can further determine the radius position PXr at which the highest quality third signal is derived among the n radius positions PXr as the third appropriate read position PXropt2b appropriate for reading the data of the track TR.

[0137] For example, from the bit error rate profile of the signal obtained by reading one round of the data of the track TR in the third read process, the sector number S (Sopt2b) when the bit error rate is the minimum and the third appropriate read offset correction amount Xcopt2b which is the read offset correction amount Xc can be obtained.

[0138] The lead position averaging processing unit 64 can derive an averaged position that is the average of the first appropriate lead position PXropt1, the second appropriate lead position PXropt2a, and the third appropriate lead position PXropt2b in the radial direction d1. Since it is possible to acquire the profiles of three systems of bit error rates, it is possible to obtain an appropriate lead offset correction amount Xcopt (appropriate lead position PXropt) with sector number dependency removed.

[0139] Accordingly, when reading the data of the track TR, the read processing unit 61b can move the read head RHD to the above-mentioned averaged position and read the data of the track TR at the above-mentioned averaged position. It becomes easier to perform the read processing by positioning the read head RHD at a more appropriate radial position PXr than in the first embodiment, and it becomes easier to obtain a higher quality signal by the read processing.

[0140] The sector SC0, the sector SC{(1 / 3)(Ns - 1)}, and the sector SC{(2 / 3)(Ns - 1)} are provided at equal intervals in the circumferential direction. There may be a case where the total number Ns of sectors SC of the track TR is not divisible by 3. In that case, in the second read processing, the read processing unit 61b first reads the data of the sector SC having a sector number S that is an integer value close to the value of {(2 / 3)(Ns - 1)}, and in the third read processing, the read processing unit 61b may first read the data of the sector SC having a sector number S that is an integer value close to the value of {(1 / 3)(Ns - 1)}.

[0141] Note that, although different from this Modification Example 1, the read processing may be performed four or more times while shifting the read start position in the circumferential direction. Since the number of systems of the profile of the bit error rate can be increased, the effect of averaging the appropriate lead position PXropt can be improved. However, it should be noted that the time period for searching for the appropriate lead position PXropt increases as the number of times of read processing performed on one track TR increases.

[0142] Also in the first modification example, the same effects as those of the first embodiment can be obtained. Further, since the measurement position can be shifted in the circumferential direction and the read process can be performed multiple times, the sector dependence of the signal quality can be averaged.

[0143] (Second modification example of the first embodiment) Next, the configuration of the magnetic disk device 1 according to the second modification example of the first embodiment will be described. FIG. 23 shows, in the second modification example, the read process performed on the target track TR while moving the read head RHD in a straight track in the first seek direction during one rotation of the disk DK, and the read process performed on the target track TR while moving the read head RHD in a straight track in the second seek direction during one rotation of the disk DK. It is a figure which shows the change of the bit error rate ER, the change of the read offset correction amount Xc, and the change of the sector number S of the target position in a graph when these are repeated.

[0144] The magnetic disk device 1 is configured in the same manner as the magnetic disk device 1 of the first embodiment except for the configuration described in the second modification example. In the first modification example, the appropriate read position PXropt can be searched for at high speed, the read process can be continuously performed multiple times without a standby operation, and the effect of averaging the appropriate read position PXropt can be improved.

[0145] As shown in FIG. 23, the read processing unit 61b performs the first read process in the same manner as in the first embodiment (FIG. 19). In the first read process, the read processing unit 61b first reads the data of the sector SC0 with the read offset correction amount Xc as Xcs (Xc[0]), and finally reads the data of the sector SCNs-1 with the read offset correction amount Xc as Xce (Xc[k-1]).

[0146] From the profile of the bit error rate of the signal obtained by reading one round of the data of track TR, the sector number S when the bit error rate is minimized, i.e., Sopt1, and the first appropriate read offset correction amount Xcopt1 which is the read offset correction amount Xc can be obtained.

[0147] The read processing unit 61b can execute the second read processing after the first read processing. In this second modification example 2, the read processing unit 61b executes the second read processing, the third read processing, and multiple read processings following the first read processing. The second read processing is a process of seeking the read head RHD at a constant speed in the second seek direction (in this example, generally the outward direction) opposite to the first seek direction within the period when the disk DK rotates m2 times, moving the read head RHD to n2 radial positions shifted from each other in the radial direction d1, and reading the data of track TR at each radial position PXr.

[0148] In this second modification example 2, the magnetic disk device 1 satisfies the relationship of the above formula 2 (1 ≤ m2 < n2). The operation of seeking the read head RHD during the second read processing is the same as the operation during the first read processing except that the seek direction is the second seek direction. In this second modification example 2, n1 = n2 and m1 = m2. In the second read processing, the read processing unit 61b first reads the data of sector SC0 with the read offset correction amount Xc as Xce(Xc[k - 1]), and finally reads the data of sector SCNs - 1 with the read offset correction amount Xc as Xcs(Xc[0]).

[0149] From the above, the range of the radial direction d1 measured in the second read process is the same as the range of the radial direction d1 measured in the first read process. That is, the radial position PXr at which the data of the track TR is read last in the first read process and the radial position PXr at which the data of the track TR is read first in the second read process are the radial position PXre and are the same. The radial position PXr at which the data of the track TR is read first in the first read process and the radial position PXr at which the data of the track TR is read last in the second read process are the radial position PXrs and are the same.

[0150] Different from the above-described Modification 1, the second read process can be carried out continuously following the first read process without sandwiching the seek operation and the standby operation. The radial position PXr at which the read head RHD is moved does not change discontinuously. Since the measurement of the quality (for example, bit error rate) of the signal obtained by reading the data of the track TR can be performed continuously instead of intermittently, the measurement of the above quality can be performed a plurality of times in a short time.

[0151] The comparison unit 62 can further compare the qualities of a plurality of second signals obtained by reading in the second read process and derive the second signal of the highest quality from among the plurality of second signals. The determination unit 63 can further determine, among the n2 radial positions PXr, the radial position PXr at which the second signal of the highest quality is derived as the second appropriate read position PXropt2a appropriate for reading the data of the track TR.

[0152] The read position averaging processing unit 64 can derive an averaging position that is the position obtained by averaging the first appropriate read position PXropt1 and the second appropriate read position PXropt2a in the radial direction d1. Thereby, when reading the data of the track TR, the read processing unit 61b can move the read head RHD to the above averaging position and read the data of the track TR at the above averaging position. It becomes easier to perform the read process by positioning the read head RHD at a more appropriate radial position PXr than in the above-described first embodiment, and it becomes easier to obtain a signal of higher quality by the read process.

[0153] The number of read operations for one track is not limited to two, and may be performed three or more times. In the second modification example, six read operations including the first read operation and the second read operation are performed. Also, the time period for performing each read operation is not limited to the period Trot during which the disk DK makes one rotation, and may be less than the period Trot, or may exceed the period Trot. Furthermore, the time periods for performing each read operation may be the same or may be different from each other.

[0154] Also in the second modification example, the same effects as those of the first embodiment can be obtained. In addition, since the number of profiles of the bit error rate can be increased, the effect of averaging the appropriate read position PXropt can be improved.

[0155] (Modification Example 3 of the First Embodiment) Next, the configuration of the magnetic disk device 1 according to the third modification example of the first embodiment will be described. FIG. 24 is a diagram showing, in the third modification example, a change in the read offset correction amount Xc with respect to the position (radial position PXr) of the target sector SC in a graph, and shows an example in which the read offset correction amount Xc is changed in a straight line orbit with an upward slope and then the read offset correction amount Xc is changed in a straight line orbit with a downward slope during one rotation of the disk DK. The magnetic disk device 1 is configured in the same manner as the magnetic disk device 1 of the second modification example except for the configuration described in the third modification example.

[0156] As shown in FIG. 24, during the period Trot in which the disk DK makes one rotation, both the first read operation of seeking the read head RHD at a constant speed in the first seek direction and the second read operation of seeking the read head RHD at a constant speed in the second seek direction may be performed. The read head RHD is reciprocated between the radial position PXrs and the radial position PXre.

[0157] From the profile of the bit error rate of the signal obtained in the first read process performed during the first half rotation of the disk DK, the sector number Sopt1 and the first appropriate read offset correction amount Xcopt1 when the bit error rate is minimized can be obtained. From the profile of the bit error rate of the signal obtained in the second read process performed during the second half rotation of the disk DK, the sector number Sopt2a and the second appropriate read offset correction amount Xcopt2a when the bit error rate is minimized can be obtained.

[0158] Also in this Modification 3, the same effects as those of the first embodiment can be obtained. Further, the appropriate read offset correction amount Xc (appropriate read position PXropt) can be obtained multiple times in a short time.

[0159] (Modification 4 of the First Embodiment) Next, the configuration of the magnetic disk device 1 according to Modification 4 of the first embodiment will be described. FIG. 25 is a diagram showing, in this Modification 4, the change in the bit error rate, the change in the read offset correction amount Xc, and the change in the sector number of the target position, respectively, in a graph when the read head RHD is moved on a linear track in the first seek direction and the read process is performed on the target track TR while the disk DK makes one rotation, and then the read head is moved on a linear track in the second seek direction and the read process is performed on the target track. The magnetic disk device 1 is configured in the same manner as the magnetic disk device 1 of Modification 2 except for the configuration described in this Modification 4.

[0160] As shown in FIG. 25, the technology of this Modification 4 corresponds to a combination of the technology of Modification 2 (FIG. 23) and the technology of Modification 3 (FIG. 24). During the period Trot in which the disk DK makes one rotation, both the first read process of seeking the read head RHD at a constant speed in the first seek direction and the second read process of seeking the read head RHD at a constant speed in the second seek direction are performed. Further, the number of times of the read process for one track TR is three or more times, for example, 12 times (6 round trips). Even in the fourth modification example, the same effects as those of the second and third modification examples can be obtained.

[0161] (Fifth Modification Example of the First Embodiment) Next, the configuration of the magnetic disk drive 1 according to the fifth modification example of the first embodiment will be described. FIG. 26 is a diagram showing, in this fifth modification example, a graph of the change in the lead-off offset correction amount Xc with respect to the position (radial position PXr) of the target sector SC. During one rotation of the disk DK, the lead-off offset correction amount Xc is changed in a straight-line trajectory with an upward slope, then continuously changed in a straight-line trajectory with a downward slope, then continuously changed in a straight-line trajectory with an upward slope, and then continuously changed in a straight-line trajectory with a downward slope. The magnetic disk drive 1 is configured in the same manner as the magnetic disk drive 1 of the third modification example except for the configuration described in this fifth modification example.

[0162] As shown in FIG. 26, the read process may be performed three or more times during the period Trot of one rotation of the disk DK. In this fifth modification example, the read process is performed four times (two round trips). Even in this fifth modification example, the same effects as those of the third modification example can be obtained.

[0163] (Sixth Modification Example of the First Embodiment) Next, the configuration of the magnetic disk drive 1 according to the sixth modification example of the first embodiment will be described. FIG. 27 is a diagram showing, in this sixth modification example, a graph of the change in the lead-off offset correction amount Xc with respect to the position (radial position PXr) of the target sector SC, and shows an example in which the lead-off offset correction amount Xc is changed in a sine-wave-shaped trajectory. The magnetic disk drive 1 is configured in the same manner as the magnetic disk drive 1 of the first embodiment except for the configuration described in this sixth modification example.

[0164] As shown in FIG. 27, when executing the first read process, the read processing unit 61b seeks the read head RHD in the first seek direction (inward direction in this example), but does not seek the read head RHD at a constant speed. The period for executing the first read process includes a first acceleration period PA1 which is the first period and a first deceleration period PD1 which is the last period. The read processing unit 61b seeks the read head RHD while gradually increasing the speed in the first seek direction during the first acceleration period PA1. The read processing unit 61b seeks the read head RHD while gradually decreasing the speed in the first seek direction during the first deceleration period PD1.

[0165] In this Modification 6, instead of seeking the read head RHD at a constant speed, the read head RHD is sought with an ease-in and ease-out. Since a rapid change in the speed of the read head RHD during seeking can be suppressed, the risk of exciting the resonance frequency of the mechanical system can be reduced.

[0166] Also, in this Modification 6, the n1 radial positions PXr are provided at equal intervals in the radial direction d1. Therefore, the read processing unit 61b reads the data of the track TR while gradually shortening the time interval during the first acceleration period PA1. The read processing unit 61b reads the data of the track TR while gradually lengthening the time interval during the first deceleration period PD1.

[0167] Also in this Modification 6, the same effects as those of the above-described first embodiment can be obtained. Note that the period for executing the first read process may further include a first constant-speed period in which the read head RHD is sought at a constant speed between the first acceleration period PA1 and the first deceleration period PD1. Even in that case, the risk of exciting the resonance frequency of the mechanical system can be reduced.

[0168] (Modification 7 of the First Embodiment) Next, the configuration of the magnetic disk drive 1 according to Modification Example 7 of the first embodiment will be described. FIG. 28 is a diagram showing changes in the lead-off offset correction amount Xc with respect to the position (radial position PXr) of the target sector SC in three types of graphs in this Modification Example 7, and shows an example in which the lead start positions are shifted in the circumferential direction three times, and the lead-off offset correction amount Xc is changed along the same sinusoidal orbit. The magnetic disk drive 1 is configured in the same manner as the magnetic disk drive 1 of the above Modification Example 6 except for the configuration described in this Modification Example 7.

[0169] As shown in FIG. 28, the technology of this Modification Example 7 corresponds to a combination of the technology of the above Modification Example 1 (FIG. 21) and the technology of the above Modification Example 6 (FIG. 27). The read processing unit 61b performs the first read processing in the same manner as in the above Modification Example 6 (FIG. 27). In the first read processing, the read processing unit 61b first reads the data of the sector SC0 with the lead-off offset correction amount Xc as Xcs (Xc[0]), and finally reads the data of the sector SCNs-1 with the lead-off offset correction amount Xc as Xce (Xc[k-1]).

[0170] From the profile of the bit error rate of the signal obtained by reading one round of the data on the track TR, the sector number S when the bit error rate is minimized, i.e., Sopt1, and the first appropriate lead-off offset correction amount Xcopt1 which is the lead-off offset correction amount Xc can be obtained.

[0171] The read processing unit 61b sequentially executes a seek operation, a rotation wait operation, and a second read processing following the first read processing. The second read processing is a process of seeking the read head RHD in the first seek direction during the period when the disk DK rotates m2 times, moving the read head RHD to n2 radial positions PXr shifted from each other in the radial direction d1, and reading the data of the track TR at each radial position PXr. In this Modification Example 7, the magnetic disk drive 1 satisfies the relationship of the above formula 2 (1 ≦ m2 < n2).

[0172] The operation of seeking the read head RHD during the second read process is the same as the operation of seeking the read head RHD during the first read process of the above Modification Example 6. In this Modification Example 7, n1 = n2 and m1 = m2. In the second read process, the read processing unit 61b first reads the data of the sector SC{(2 / 3)(Ns - 1)} with the read offset correction amount Xc as Xcs(Xc[0]), and finally reads the data of the sector SC{(2 / 3)(Ns - 1)-1} with the read offset correction amount Xc as Xce(Xc[k - 1]).

[0173] The position (sector SC0) where the data of the track TR is first read in the first read process and the position (sector SC{(2 / 3)(Ns - 1)}) where the data of the track TR is first read in the second read process are shifted from each other in the circumferential direction. As described above, it can be seen that in each of the first read process and the second read process, the read offset correction amount Xc is changed in the same sinusoidal orbit.

[0174] The comparison unit 62 can further compare the qualities of a plurality of second signals obtained by the read in the second read process, and derive the second signal with the highest quality from among the plurality of second signals. The determination unit 63 can further determine the radius position PXr at which the highest quality second signal is derived among the n2 radius positions PXr as the second appropriate read position PXropt2a appropriate for reading the data of the track TR.

[0175] For example, from the profile of the bit error rate of the signal obtained by reading one round of the data of the track TR in the second read process, the sector number Sopt2a and the second appropriate read offset correction amount Xcopt2a when the bit error rate is minimized can be obtained.

[0176] The lead position averaging processing unit 64 can derive an averaged position that is the average of the first appropriate lead position PXropt1 and the second appropriate lead position PXropt2a in the radial direction d1. Thereby, when reading the data of the track TR, the lead processing unit 61b can move the lead head RHD to the above-mentioned averaged position and read the data of the track TR at the above-mentioned averaged position. It becomes easier to position the lead head RHD at a more appropriate radial position PXr than in the above-mentioned modification 6 and perform the lead processing, and it becomes easier to obtain a higher quality signal by the lead processing.

[0177] The number of times of lead processing for one track is not limited to two and may be performed three or more times. In this modification 7, the lead processing including the above-mentioned first lead processing and the above-mentioned second lead processing is performed three times. In each of the three lead processings, the lead offset correction amount Xc is changed on the same in-and-out track.

[0178] The lead processing unit 61b sequentially executes a seek operation, a rotation wait operation, and a third lead processing following the second lead processing. The third lead processing is the same as the above-mentioned modification 1 (FIG. 21) except for the lead offset correction amount Xc.

[0179] The comparison unit 62 can further compare the qualities of a plurality of third signals obtained by leading in the third lead processing and derive the highest quality third signal from among the plurality of third signals. The determination unit 63 can further determine the radial position PXr at which the highest quality third signal is derived among the n radial positions PXr as the third appropriate lead position PXropt2b that is appropriate for reading the data of the track TR.

[0180] For example, from the bit error rate profile of the signal obtained by leading one round of the data of the track TR in the third lead processing, the sector number Sopt2b when the bit error rate is the minimum and the third appropriate lead offset correction amount Xcopt2b that is the lead offset correction amount Xc can be obtained.

[0181] The lead position averaging processing unit 64 can derive an averaged position that is the averaged position of the first appropriate lead position PXropt1, the second appropriate lead position PXropt2a, and the third appropriate lead position PXropt2b in the radial direction d1. An appropriate lead offset correction amount Xcopt (appropriate lead position PXropt) with sector number dependency removed can be obtained.

[0182] Accordingly, when reading the data of the track TR, the read processing unit 61b can move the read head RHD to the averaged position and read the data of the track TR at the averaged position. Also in the present Modification 7, the same effects as those of the above-described Modification 1 and Modification 6 can be obtained.

[0183] (Modification 8 of the First Embodiment) Next, the configuration of the magnetic disk device 1 according to Modification 8 of the first embodiment will be described. FIG. 29 is a diagram showing, in the present Modification 8, a change in the lead offset correction amount Xc with respect to the position (radial position PXr) of the target sector SC in a graph, and shows an example in which the lead offset correction amount Xc is changed in a sinusoidal trajectory with an upward slope and then continuously changed in a sinusoidal trajectory with a downward slope during one rotation of the disk DK. The magnetic disk device 1 is configured in the same manner as the magnetic disk device 1 of the above-described Modification 6 except for the configuration described in the present Modification 8.

[0184] As shown in FIG. 29, the technique of the present Modification 8 corresponds to a combination of the technique of the above-described Modification 3 (FIG. 24) and the technique of the above-described Modification 6 (FIG. 27). During the period Trot in which the disk DK makes one rotation, both the first read processing of seeking the read head RHD in and out in the first seek direction and the second read processing of seeking the read head RHD in and out in the second seek direction may be performed. The read head RHD is reciprocated between the radial position PXrs and the radial position PXre.

[0185] Specifically, the read processing unit 61b executes a second read process after the first read process. The second read process is a process of seeking the read head RHD in the second seek direction within a period during which the disk DK rotates m2 times, moving the read head RHD to n2 radial positions PXr that are displaced from each other in the radial direction d1, and reading the data of the track TR at each radial position PXr. In the present modification 8, the magnetic disk device 1 satisfies the relationship of the above formula 2 (1 ≦ m2 < n2). In the present modification 8, n1 = n2 and m1 = m2.

[0186] The period for executing the second read process includes a second acceleration period PA2 that is the first period and a second deceleration period PD2 that is the last period. The read processing unit 61b seeks the read head RHD while gradually increasing the speed in the second seek direction during the second acceleration period PA2. The read processing unit 61b seeks the read head RHD while gradually decreasing the speed in the second seek direction during the second deceleration period PD2.

[0187] In the present modification 8, the n2 radial positions PXr are provided at equal intervals in the radial direction d1. Therefore, the read processing unit 61b reads the data of the track TR while gradually shortening the time interval during the second acceleration period PA2. The read processing unit 61b reads the data of the track TR while gradually lengthening the time interval during the second deceleration period PD2.

[0188] From the profile of the bit error rate of the signal obtained by the first read process performed during the period when the disk DK rotates the first half, the sector number Sopt1 and the first appropriate read offset correction amount Xcopt1 when the bit error rate is minimized can be obtained. From the profile of the bit error rate of the signal obtained by the second read process performed during the period when the disk DK rotates the remaining half, the sector number Sopt2a and the second appropriate read offset correction amount Xcopt2a when the bit error rate is minimized can be obtained.

[0189] Even in the eighth modification example, the same effects as those of the third and sixth modification examples can be obtained. Note that the period during which the second read process is executed may further include a second constant speed period during which the read head RHD is seeked at a constant speed between the second acceleration period PA2 and the second deceleration period PD2.

[0190] (Second Embodiment) Next, the configuration of the magnetic disk device 1 according to the second embodiment will be described. FIG. 30 is a diagram showing, in the magnetic disk device 1 according to the second embodiment, changes in the bit error rate ER, changes in the read offset correction amount Xc, and changes in the sector number of the target position when a read process, a seek operation, and a standby operation are repeatedly performed on the target track TR, respectively, in a graph, and is a diagram showing an example in which the bit error rate ER is precisely measured in a second range narrower than the first range after roughly measuring the bit error rate ER in the first range. The magnetic disk device 1 is configured in the same manner as the magnetic disk device 1 of the first embodiment except for the configuration described in the second embodiment.

[0191] As shown in FIG. 30, the read processing unit 61b performs the first read process within the first range in the same manner as in the first embodiment (FIG. 17). In the first read process, the read processing unit 61b first reads the data of the sector SC0 with the read offset correction amount Xc[i] as Xcs (Xc[0]), and finally reads the data of the sector SCNs-1 with the read offset correction amount Xc[i] as Xce (Xc[k-1]). The first range is a range in the radial direction d1, a range to which all n1 radial positions PXr belong, and a range from the radial position PXrs to the radial position PXre.

[0192] From the profile of the bit error rate of the signal obtained by reading one round of the data of the track TR, the sector number S (Sopt1) when the bit error rate is minimized and the first appropriate read offset correction amount Xcopt1, which is the read offset correction amount Xc, can be obtained, and the first appropriate read position PXropt1 can also be obtained.

[0193] Incidentally, the first appropriate lead offset correction amount Xcopt1 obtained in the first lead process is a rough adjustment value, and the first appropriate lead position PXropt1 is a rough adjustment position. Therefore, while satisfying the prerequisite for quickly searching for an appropriate lead position as in the second embodiment, an appropriate lead offset correction amount Xcopt that is a more appropriate fine adjustment value than the first appropriate lead offset correction amount Xcopt1, and an appropriate lead position PXropt that is a more appropriate fine adjustment position than the first appropriate lead position PXropt1 may be further derived.

[0194] Therefore, the lead processing unit 61b repeatedly executes a set of sequentially performing a seek operation, a rotation wait operation, and a third lead process a plurality of times after the first lead process. The lead processing unit 61b performs the third lead process within the second range. The second range is a range to which the first appropriate lead position PXropt1 belongs, is narrower than the first range in the radial direction d1, and is a range to which n3 radial positions PXr shifted from each other in the radial direction d1 belong.

[0195] In the second embodiment, the second range includes both sides of the first appropriate lead position PXropt1. The n3 radial positions PXr of the second range include one or more radial positions PXr located on the outer circumference OD side than the first appropriate lead position PXropt1 and one or more radial positions PXr located on the inner circumference ID side than the first appropriate lead position PXropt1.

[0196] Also, in the second embodiment, the n3 radial positions PXr are selected from the n1 radial positions PXr. However, the n3 radial positions PXr do not necessarily have to be selected from the n1 radial positions PXr. In that case, for example, in the radial direction d1, the interval between the n3 radial positions PXr may be narrower than the interval between the n1 radial positions PXr.

[0197] In each of the above sets, the read processing unit 61b executes a seek operation to move the read head RHD to one of the n3 radial positions PXr, executes a rotation wait operation while holding the read head RHD in a state facing the one radial position PXr, and executes a third read processing for reading the data of the track TR a plurality of times at the one radial position PXr.

[0198] The signal quality averaging processing unit 65 can derive a plurality of averaging qualities. Each averaging quality is a quality obtained by averaging the qualities of a plurality of third signals obtained by a plurality of reads by the third read processing at a corresponding one of the n3 radial positions PXr.

[0199] The comparison unit 62 can further compare a plurality of averaging qualities and derive the highest-quality averaging quality from among the plurality of averaging qualities. The determination unit 63 can further determine that, among the n3 radial positions PXr, the radial position PXr at which the highest-quality averaging quality is derived is a third appropriate read position PXropt3 that is more appropriate for reading the data of the track TR than the first appropriate read position PXropt1. Thereby, when reading the data of the track TR, the read processing unit 61b can move the read head RHD to the third appropriate read position PXropt3 and read the data of the track TR at the third appropriate read position PXropt3.

[0200] FIG. 31 is a flowchart for explaining a method of searching for a third appropriate read offset correction amount Xcopt3 applicable to the magnetic disk device 1 of the second embodiment. FIG. 32 is a flowchart for explaining the above method following FIG. 31. FIG. 33 is a flowchart for explaining the above method following FIG. 32. As shown in FIG. 31, when a method of searching for the third appropriate read offset correction amount Xcopt3 for the track TR is started, first, in step STb1, the read processing unit 61b initializes the sector number S of the target position to 0 (S = 0).

[0201] Subsequently, in step STb2, the read processing unit 61b moves and positions the read head RHD at the radial position PXr(S) within the first range. Then, in step STb3, the read channel 14R measures the bit error rate ER(S). The radial position PXr(S) is a position that is separated from the reference position by a distance Xr(S) (Xr(S) = Xw + Xs + Xc(S)). The first range is a range having a width in the radial direction d1, which is a range from the radial position PXrs to the radial position PXre.

[0202] Thereafter, in step STb4, the read processing unit 61b increments the sector number S of the target position. Subsequently, in step STb5, the read processing unit 61b determines whether the sector number S of the target position has exceeded the final sector number Ns - 1. If the sector number S has not exceeded the sector number Ns - 1 (S ≤ Ns - 1), the process proceeds to step STb2, and the processes of steps STb2 to STb5 are repeatedly executed.

[0203] On the other hand, in step STb5, if it is determined that the sector number S of the target position has exceeded the sector number Ns - 1 (S = Ns), the measurement of the bit error rate ER within the first range is completed, and the process proceeds to step STb6. In step STb6, the comparison unit 62 compares the bit error rates ER of the plurality of first signals obtained by the read in the first read process, and derives the first signal having the minimum (preferably, minimum) bit error rate ER from among the plurality of first signals. Then, it is possible to search for Smin, which is the sector number S when the first signal having the minimum bit error rate ER is derived.

[0204] Next, in step STb7, the determination unit 63 determines that the read offset correction amount Xc[Smin] when reading the sector SCmin having the sector number S of Smin is the first appropriate read offset correction amount Xcopt1 (Xcopt1 = Xc[Smin]).

[0205] As shown in FIG. 32, subsequently, in step STb8, the read processing unit 61b sets a second range that is narrower than the first range. The second range includes the radius position PXropt1 that is the first appropriate read position PXropt1. The radius position PXropt1 is a position moved by (Xw + Xs + Xcopt1) from the reference position. The read offset correction amount Xc when executing the third read processing within the second range is Xc[v]. For example, the read processing unit 61b can set the read offset correction amounts Xc[0], Xc[1], Xc[2], Xc[3], Xc[4] at five radius positions PXr using the following equation 3 (n3 = 5). Xc[v]=Xcopt1+(v - 2)×ΔQ … Equation 3 Here, the step width of the read offset correction amount Xc is ΔQ. Thereafter, in step STb9, the read processing unit 61b initializes the index v to 0 (v = 0). Subsequently, in step STb10, the read processing unit 61b moves and positions the read head RHD to the radius position PXr[v] within the second range. Then, in step STb11, the read channel 14R measures a plurality of bit error rates ER[v] for one round of the track TR1 at the radius position PXr[v], and the signal quality averaging unit 65 derives the average value of the plurality of bit error rates ER[v].

[0206] Thereafter, in step STb12, the read processing unit 61b increments the index v. Subsequently, in step STb13, the read processing unit 61b determines whether the index v has exceeded the set value of 5. If the index v has not exceeded 5 (v < 5), the process proceeds to step STb10, and the processes of steps STb10 to STb13 are repeatedly executed.

[0207] On the other hand, in step STb13, when it is determined that the index v has exceeded 5 (set value) (v > 5), the measurement of the bit error rate ER within the second range has ended, and the process proceeds to step STb14. In step STb14, the comparison unit 62 compares a plurality of average values obtained by reading through the third read process, and derives an average value with the minimum (preferably minimum) bit error rate ER from among the plurality of average values. Then, it is possible to search for vmin, which is the index v when the minimum average value is derived.

[0208] Then, the determination unit 63 can determine that the read offset correction amount Xc[vmin] when the index v is set to vmin is the third appropriate read offset correction amount Xcopt3. Thereby, the method for searching for the third appropriate read offset correction amount Xcopt3 for the track TR is completed.

[0209] According to the magnetic disk device 1 according to the second embodiment configured as described above and the method for searching for the third appropriate read position PXropt3, this second embodiment can obtain the same effects as the first embodiment. After roughly measuring a wide first range to derive the first appropriate read position PXropt1 (the first appropriate read offset correction amount Xcopt1), it is possible to derive the third appropriate read position PXropt3 (the third appropriate read offset correction amount Xcopt3) by narrowing down to a narrower second range and precisely measuring.

[0210] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope. If necessary, it is also possible to combine two or more of the plurality of embodiments and the plurality of modification examples.

Explanation of Reference Numerals

[0211] 1... magnetic disk device, 20... SPM, 24... VCM, 30... arm, HD... head, WHD... write head, RHD... read head, 60... MPU, 61... read / write processing unit, 61a... write processing unit, 61b... read processing unit, 62... comparison unit, 63... determination unit, 64... read position averaging processing unit, 65... signal quality averaging processing unit, 70... volatile memory, 80... buffer memory, 90... non-volatile memory, 100... host, 110... system controller, 120... driver IC, 140... R / W channel, 14R... read channel, 14W... write channel, 150... HDC, DK... disk, L... recording layer, TR... track, SC... sector, P... actuator, PXr... radial position, PXropt... appropriate read position, Xc... read offset correction amount, Xcopt... appropriate read offset correction amount, ID... inner circumference, OD... outer circumference, AP... amplitude, ER... bit error rate, PA... acceleration period, PD... deceleration period, d1... radial direction, d2... traveling direction, d3... rotational direction.

Claims

1. A disk having tracks on a recording layer, a read head for reading data from the recording layer of the disk, a read processing unit that, within a period during which the disk rotates m1 times, moves the read head to n1 radial positions that are displaced from each other in the radial direction of the disk, and executes a first read process of reading data of the track at each of the radial positions, a comparison unit that compares the qualities of a plurality of first signals obtained by reading in the first read process, and derives a first signal of the highest quality from among the plurality of first signals, a control unit having a determination unit that determines, among the n1 radial positions, the radial position at which the first signal of the highest quality is derived as a first appropriate read position that is appropriate for reading data of the track, where 1 ≤ m1 < n1, a magnetic disk device.

2. When reading data of the track, the read processing unit moves the read head to the first appropriate read position, and reads the data of the track at the first appropriate read position. The magnetic disk device according to Claim 1.

3. Further comprising a read channel that measures the qualities of the plurality of first signals obtained by reading in the first read process. The magnetic disk device according to Claim 1.

4. The quality of the plurality of first signals is the amplitude of the plurality of first signals, and the first signal of the highest quality is the signal having the maximum amplitude among the plurality of first signals. The magnetic disk device according to Claim 1.

5. The first signal of the highest quality is the signal having the maximum amplitude among the plurality of first signals. The magnetic disk device according to Claim 4.

6. The quality of the plurality of first signals is the bit error rate of the plurality of first signals, and the first signal of the highest quality is the signal having the minimum bit error rate among the plurality of first signals. The magnetic disk device according to Claim 1.

7. The first signal of the highest quality is the signal having the minimum bit error rate among the plurality of first signals. The magnetic disk device according to Claim 6.

8. When executing the first read process, the read processing unit seeks the read head at a constant speed in a first seek direction. The magnetic disk device according to Claim 1.

9. The n1 radial positions are provided at equal intervals in the radial direction, When executing the first read process, The read processing unit reads the data of the track at regular time intervals. The magnetic disk device according to claim 8.

10. The read processing unit sequentially executes a seek operation, a rotation wait operation, and a second read processing following the first read processing. The second read processing is a process of seeking the read head in the first seek direction within a period in which the disk rotates m2 times, moving the read head to n2 radial positions shifted from each other in the radial direction, and reading the data of the track at each of the radial positions. 1 ≤ m2 < n2. The operation of seeking the read head during the second read processing is the same as the operation of seeking the read head during the first read processing. The position where the data of the track is first read in the first read processing and the position where the data of the track is first read in the second read processing are shifted from each other in the circumferential direction of the disk. The magnetic disk device according to claim 8.

11. The read processing unit executes a second read processing after the first read processing. The second read processing is a process of seeking the read head at a constant speed in a second seek direction opposite to the first seek direction within a period in which the disk rotates m2 times, moving the read head to n2 radial positions shifted from each other in the radial direction, and reading the data of the track at each of the radial positions. 1 ≤ m2 < n2. The magnetic disk device according to claim 8.

12. The radial position where the data of the track is last read in the first read processing and the radial position where the data of the track is first read in the second read processing are the same. The radial position where the data of the track is first read in the first read processing and the radial position where the data of the track is last read in the second read processing are the same. The magnetic disk device according to claim 11.

13. The period for executing the first read processing includes a first acceleration period which is the first period and a first deceleration period which is the last period. The read processing unit In the first acceleration period, the read head is sought while gradually increasing the speed in the first seek direction. In the first deceleration period, the read head is sought while gradually decreasing the speed in the first seek direction. The magnetic disk device according to claim 1.

14. The n1 radius positions are provided at equal intervals in the radial direction. The read processing unit reads the data of the track while gradually shortening the time interval during the first acceleration period. reads the data of the track while gradually lengthening the time interval during the first deceleration period. The magnetic disk device according to claim 13.

15. The read processing unit sequentially executes a seek operation, a rotation wait operation, and a second read processing following the first read processing. The second read processing is a process of seeking the read head in the first seek direction within a period in which the disk rotates m2 times, moving the read head to n2 radius positions shifted from each other in the radial direction, and reading the data of the track at each of the radius positions. 1 ≤ m2 < n2. The operation of seeking the read head during the second read processing is the same as the operation of seeking the read head during the first read processing. The position where the data of the track is first read in the first read processing and the position where the data of the track is first read in the second read processing are shifted from each other in the circumferential direction of the disk. The magnetic disk device according to claim 13.

16. The read processing unit executes a second read processing after the first read processing. The second read processing is a process of seeking the read head in a second seek direction opposite to the first seek direction within a period in which the disk rotates m2 times, moving the read head to n2 radius positions shifted from each other in the radial direction, and reading the data of the track at each of the radius positions. 1 ≤ m2 < n2. The period for executing the second read processing includes a second acceleration period which is the first period and a second deceleration period which is the last period. The read processing unit seeks the read head while gradually increasing the speed in the second seek direction during the second acceleration period. seeks the read head while gradually decreasing the speed in the second seek direction during the second deceleration period. The magnetic disk device according to claim 13.

17. The control unit further includes a read position averaging processing unit. The comparison unit further compares the qualities of a plurality of second signals obtained by reading in the second read processing, and derives the second signal with the highest quality from among the plurality of second signals. The determination unit further determines, among the n2 radial positions, the radial position at which the second signal of the highest quality is derived as a second appropriate read position appropriate for reading the data of the track. The read position averaging unit derives, in the radial direction, an averaged position that is an average of the first appropriate read position and the second appropriate read position. When reading the data of the track, the read processing unit moves the read head to the averaged position and reads the data of the track at the averaged position. The magnetic disk device according to any one of claims 10, 11, 15, and 16.

18. The control unit further includes a signal quality averaging unit. A range in the radial direction, within which all of the n1 radial positions belong, is defined as a first range. If a range to which the first appropriate read position belongs and which is narrower than the first range in the radial direction, and within which n3 radial positions shifted from each other in the radial direction belong, is defined as a second range. After the first read process, the read processing unit repeatedly executes a plurality of sets of sequentially performing a seek operation, a rotation waiting operation, and a third read process. In each of the sets, the read processing unit executes the seek operation to move the read head to one of the n3 radial positions. executes the rotation waiting operation while holding the read head in a state facing the one radial position. executes the third read process of reading the data of the track a plurality of times at the one radial position. The signal quality averaging unit derives a plurality of averaged qualities. Each of the averaged qualities is a quality obtained by averaging the qualities of a plurality of third signals obtained by a plurality of reads by the third read process at a corresponding one of the n3 radial positions. The comparison unit further compares the plurality of averaged qualities and derives the averaged quality of the highest quality from among the plurality of averaged qualities. The determination unit further determines, among the n3 radial positions, the radial position at which the highest quality averaged quality is derived as a third appropriate read position more appropriate for reading the data of the track than the first appropriate read position. When reading the data of the track, the read processing unit moves the read head to the third appropriate read position and reads the data of the track at the third appropriate read position. The magnetic disk device according to claim 1.

19. The n3 radial positions in the second range are one or more radial positions located on the outer peripheral side of the first appropriate lead position and one or more radial positions located on the inner peripheral side of the first appropriate lead position, and The magnetic disk device according to claim 18.

20. A write head for writing data to the recording layer of the disk, and An arm supporting the read head and the write head, further comprising: The control unit further has a write processing unit that moves the read head to a standby position and executes a write process for writing data to the track. When the first appropriate lead position is a position offset from the standby position and data on the track is read, the read processing unit moves the read head to the first appropriate lead position offset from the standby position and reads the data on the track at the first appropriate lead position. When the first appropriate lead position coincides with the standby position and data on the track is read, the read processing unit moves the read head to the first appropriate lead position that is the standby position and reads the data on the track at the first appropriate lead position. The magnetic disk device according to claim 1.

Images