Magnetic disk device

Abstract

Provided is a magnetic disk device capable of suppressing errors in the positions of a target track and a magnetic head during a write operation. A controller of a magnetic disk device operates as follows in a first operation of writing to a data region while positioning a magnetic head. Namely, the controller demodulates the pulse train pattern to obtain a first pulse train demodulated value, and corrects the first pulse train demodulated value on the basis of a correction algorithm using a first set value as an independent variable. The controller calculates an offset amount of the magnetic head from one of the plurality of servo tracks on the basis of the corrected first pulse train demodulation value.

Description

[0001] This application claims the priority of Japanese Patent Application No. 2023-094930 (filing date: June 8, 2023) as a basic application. The present application incorporates the entire contents of the basic application by reference. Technical Field

[0002] This embodiment relates to a magnetic disk device. Background Art

[0003] Conventionally, a magnetic disk device positions a magnetic head based on servo data recorded on a magnetic disk. A magnetic disk is provided with a plurality of tracks. The magnetic disk device positions the magnetic head at a target track during a write operation or a read operation. Summary of the invention

[0004] An embodiment of the present invention provides a magnetic disk device capable of suppressing an error between a target track and a position of a magnetic head during a write operation.

[0005] According to the present embodiment, the magnetic disk device comprises a magnetic disk, a magnetic head, a memory and a controller. The magnetic disk comprises a plurality of servo tracks, and a plurality of servo sectors each recording servo data including a burst pattern are arranged at intervals in the circumferential direction on the plurality of servo tracks. A data area for writing data is arranged between the servo sectors arranged in the circumferential direction. The magnetic head performs writing and reading on the magnetic disk. A first set value is stored in the memory. The controller acts as follows in the first action of positioning the magnetic head while writing to the data area. That is, the controller demodulates the burst pattern to obtain a first burst demodulation value, and corrects the first burst demodulation value based on a correction algorithm using the first set value as an independent variable. Moreover, the controller calculates the offset amount of the magnetic head from one of the plurality of servo tracks based on the second burst demodulation value which is the corrected first burst demodulation value. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic diagram showing an example of the configuration of a magnetic disk device according to an embodiment.

[0007] Figure 2 This is a schematic diagram showing an example of the structure of a magnetic disk according to the embodiment.

[0008] Figure 3 FIG. 1 is a diagram showing an example of servo data recorded in a servo sector according to the embodiment.

[0009] Figure 4 It is a schematic diagram showing an example of the configuration of an N pulse train and a Q pulse train recorded in a servo sector according to the embodiment.

[0010] Figure 5 This is a diagram for explaining an example of a method for learning the RRO correction amount.

[0011] Figure 6 FIG. 1 is a diagram showing an example of position errors observed in a writing operation and a non-writing operation.

[0012] Figure 7 This is a schematic diagram showing an example of a functional configuration related to positioning control of a magnetic disk device according to an embodiment.

[0013] Figure 8 This is a flowchart showing an example of the operation of generating correction setting information according to the embodiment.

[0014] Fig. 9 This is a flowchart showing an example of the positioning operation in the non-writing operation.

[0015] Fig.10 This is a flowchart showing an example of a positioning operation in a writing operation.

[0016] Fig.11 This is a diagram showing an example of the amplitude of the demodulated signal of the N pulse train and the amplitude of the demodulated signal of the Q pulse train in a pulse train demodulation value set in a non-write operation.

[0017] Fig.12 This is a diagram showing an example of the phase of the demodulated signal of the N pulse train and the phase of the demodulated signal of the Q pulse train in the pulse train demodulation value set in the non-writing operation.

[0018] Fig.13 This is a diagram showing an example of the amplitude of the demodulated signal of the N pulse train and the amplitude of the demodulated signal of the Q pulse train in the pulse train demodulation value set during the write operation.

[0019] Fig.14 This is a diagram showing an example of the phase of the demodulated signal of the N pulse train and the phase of the demodulated signal of the Q pulse train in the pulse train demodulation value set during the write operation.

[0020] Fig.15 This is a graph obtained by plotting on a two-dimensional plane the initial phase-corrected pulse train data calculated based on the pulse train demodulation value set in non-writing action and the initial phase-corrected pulse train data calculated based on the pulse train demodulation value set in writing action without correction using correction setting information.

[0021] Fig.16 This is a diagram showing an example of the amplitude ratio in the correction setting information.

[0022] Fig.17 This is a diagram showing an example of the phase difference in the correction setting information.

[0023] Fig.18 This diagram shows an example of the difference observed in multiple servo sectors SV on a certain servo track between a second servo demodulation position calculated based on a pulse train demodulation value set in a non-write action and a second servo demodulation position calculated based on a pulse train demodulation value set in a write action without correction using correction setting information.

[0024] Fig.19 This diagram shows an example of the difference observed in multiple servo sectors SV on a certain servo track between a second servo demodulation position calculated based on a pulse train demodulation value set in a non-write operation and a second servo demodulation position calculated by performing correction using correction setting information based on a pulse train demodulation value set in a write operation.

[0025] Fig. 20 This diagram shows an example of the difference observed in a plurality of servo sectors SV on a certain servo track between a second servo demodulation position calculated based on a burst demodulation value set in a non-writing operation and a second servo demodulation position calculated by correcting only the amplitude based on a burst demodulation value set in a writing operation.

[0026] Description of symbols

[0027] 1 disk device; 2 host; 11 disk; 12 SPM; 13 ramp (ramp, start and stop area); 15 actuator arm (actuatorarm); 16 VCM; 21 SVC; 22 head; 22r read head; 22w write head; 23 HDC; 24 preamplifier; 25 RWC; 26 processor; 28 FROM; 29 DRAM; 30 controller; 41 servo track; 251 Gray code demodulation unit; 252 pulse train demodulation unit; 261 first correction unit; 262 second correction unit; 263 third correction unit; 264 correction setting information generation unit; 300 correction setting information. DETAILED DESCRIPTION

[0028] Hereinafter, a magnetic disk device according to an embodiment will be described in detail with reference to the drawings. However, the present invention is not limited to the embodiment.

[0029] (Implementation Method)

[0030] Figure 1 It is a schematic diagram showing an example of the structure of the magnetic disk device 1 according to the embodiment.

[0031] The magnetic disk device 1 is connected to a host computer 2. The magnetic disk device 1 can receive access commands such as write commands and read commands from the host computer 2.

[0032] The magnetic disk device 1 includes a magnetic disk 11 having a magnetic layer formed on the surface thereof. The magnetic disk device 1 accesses the magnetic disk 11 according to an access command. The access includes writing and reading data.

[0033] Data is written and read by a magnetic head 22. Specifically, the magnetic disk device 1 includes, in addition to the magnetic disk 11, a spindle motor (SPM) 12, a ramp 13, an actuator arm 15, a voice coil motor (VCM) 16, a servo controller (SVC) 21, a magnetic head 22, a hard disk controller (HDC) 23, a preamplifier 24, a read / write channel (RWC) 25, a processor 26, a FROM (Flash Read Only Memory) 28, and a DRAM (Dynamic Random Access Memory) 29.

[0034] The magnetic disk 11 is rotated at a predetermined rotation speed by the SPM 12 which is coaxially mounted.

[0035] The SVC 21 is an integrated circuit having a function as a driver for driving the SPM 12 and the VCM 16 . The processor 26 controls the rotation of the SPM 12 and the rotation of the VCM 16 via the SVC 21 .

[0036] The magnetic head 22 writes and reads the magnetic disk 11 through the write head 22w and the read head 22r it has. In addition, the magnetic head 22 is installed at the front end of the actuator arm 15. The magnetic head 22 moves along the radial direction of the magnetic disk 11 through the VCM 16 driven by the SVC 21. In addition, either one of the write head 22w and the read head 22r of the magnetic head 22 or both of them can also be provided with multiple numbers for a single magnetic head 22.

[0037] When the rotation of the magnetic disk 11 stops, the magnetic head 22 moves onto the ramp 13. The ramp 13 is configured to hold the magnetic head 22 at a position away from the magnetic disk 11.

[0038] The preamplifier 24 is an integrated circuit that performs writing and reading of data via the magnetic head 22. The preamplifier 24 amplifies and outputs a signal read from the magnetic disk 11 by the magnetic head 22 during a read operation, and supplies it to the RWC 25. In addition, the preamplifier 24 amplifies a signal corresponding to the data to be written supplied from the RWC 25 during a write operation, and supplies it to the magnetic head 22.

[0039] The HDC 23 controls data transmission and reception with the host 2 via the I / F bus, controls the DRAM 29 , and the like.

[0040] The DRAM 29 is used as a buffer for data transmitted and received with the host 2. For example, the DRAM 29 is used to temporarily store data to be written or data read from the magnetic disk 11.

[0041] The DRAM 29 is used as an operation memory by the processor 26. The DRAM 29 is used as an area for loading a firmware program and an area for temporarily storing various management data.

[0042] The RWC 25 modulates the write target data supplied from the HDC 23 and supplies the modulated data to the preamplifier 24. The RWC 25 also performs demodulation including error correction on the signal read from the magnetic disk 11 and supplied from the preamplifier 24, and then outputs the signal to the HDC 23 as digital data.

[0043] The processor 26 is, for example, a CPU (Central Processing Unit) and is connected to a FROM (Flash Read Only Memory) 28 and a DRAM 29 .

[0044] The FROM 28 stores a firmware program and various setting information. Alternatively, the firmware program may be stored in the magnetic disk 11 .

[0045] The processor 26 controls the entire disk device 1 according to the firmware program stored in the FROM 28 or the disk 11. For example, the processor 26 loads the firmware program from the FROM 28 or the disk 11 into the DRAM 29, and controls the SVC 21, the preamplifier 24, the RWC 25, the HDC 23, etc. according to the firmware program loaded into the DRAM 29.

[0046] Furthermore, part or all of the functions of the processor 26 may be realized by a hardware circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0047] The HDC 23, the RWC 25, and the processor 26 constitute a single integrated circuit, a SoC (System-On-a-Chip) 30. The SoC 30 may include other elements (for example, a FROM 28 or a DRAM 29) in addition to these. The SoC 30 is an example of a controller.

[0048] Figure 2 1 is a schematic diagram showing an example of the structure of the magnetic disk 11 of the embodiment. In addition, this figure shows an example of the rotation direction of the magnetic disk 11. The magnetic head 22 moves relative to the magnetic disk 11 by the rotation of the magnetic disk 11. Therefore, the write / read direction, that is, the direction in which data along the circumferential direction is written or read by the magnetic head 22 is the opposite direction of the rotation direction of the magnetic disk 11.

[0049] In the radial direction, the direction from the edge to the center of the magnetic disk 11 is the inner diameter (ID) direction, and the direction from the center to the edge of the magnetic disk 11 is the outer diameter (OD) direction.

[0050] Servo data for positioning the magnetic head 22 is written to the magnetic disk 11 by, for example, a servo writer or self-servo writing (SSW) during the manufacturing process. Figure 2 As an example of the arrangement of the servo areas in which the servo information is written, a plurality of servo areas SV are formed which are radially arranged in the radial direction and are arranged at predetermined intervals in the circumferential direction. A data area DA in which data is written is arranged between two servo areas SV which are continuous in the circumferential direction.

[0051] A plurality of servo tracks 41 are provided concentrically in the radial direction of the magnetic disk 11. The servo data written in the servo area SV is used for positioning control of the magnetic head 22.

[0052] In more detail, a plurality of concentric data tracks are arranged on an area of ​​the disk 11 where a plurality of servo tracks 41 are arranged. The plurality of servo tracks 41 can be used as a plurality of data tracks, or a plurality of data tracks different from the plurality of servo tracks 41 can be arranged. In an area divided by the data area DA on each data track, a plurality of data sectors are arranged in a circumferential direction. In each data sector, data can be written by the magnetic head 22. In addition, the data that can be written to each data sector includes user data received from the host 2, metadata (such as error correction code) attached to the user data, system data, etc. The magnetic disk device 1 retains the setting of the positional relationship between the plurality of servo tracks 41 and the plurality of data tracks in advance. The magnetic disk device 1 performs positioning control to position the magnetic head 22 on the target data track based on the servo data recorded in the servo area SV. The positioning control includes the action of moving the magnetic head 22 to the target data track in the radial direction, i.e., the seek action, and the tracking action of maintaining the magnetic head 22 on the target data track.

[0053] The area divided by the servo region SV on the servo track 41 is referred to as a servo sector SV. That is, on the plurality of servo tracks 41, a plurality of servo sectors SV are arranged at intervals in the circumferential direction.

[0054] Figure 3 This is a diagram showing an example of servo data recorded in a servo sector SV according to an embodiment. Here, it is assumed that one servo sector SV has a width approximately equivalent to three data tracks in the radial direction. This figure shows the structure of a servo sector SV spanning three data tracks #M-1, #M, and #M+1.

[0055] like Figure 3 As shown, in the servo sector SV, a preamble, a servo mark, a Gray code, an N pulse train, a Q pulse train, and a post code are recorded in this order along the write / read direction.

[0056] The preamble is a single-cycle pattern data that changes periodically in the circumferential direction. When the servo waveform read by the reading head 22r is taken into the RWC 25 as sampling data based on the servo clock, the preamble is used to adjust the amplitude, phase and frequency of the sampling data.

[0057] The servo mark is pattern data for determining the demodulation timing of servo data. The controller 30 determines the demodulation timing of various servo data to be read by the read head 22r based on the detection timing of the servo mark.

[0058] The Gray code includes a cylinder address for identifying each servo track 41 provided on the magnetic disk 11 and a sector address for identifying each servo sector SV on the servo track 41 .

[0059] The N burst and the Q burst are pattern data for detecting the position deviation from the track center of the servo track 41 indicated by the cylinder address included in the Gray code. The position deviation from the track center of the servo track 41 is referred to as a burst offset.

[0060] Figure 4 1 is a schematic diagram showing an example of the configuration of the N pulse train and the Q pulse train recorded in the servo sector SV according to the embodiment. In this figure, the dotted pattern represents one of two values ​​of different polarity (e.g., magnetization of + polarity), and the white pattern represents the other of the two values ​​(e.g., magnetization of - polarity).

[0061] The length in the radial direction may be expressed in servo track units, in other words, units of length in space when the servo track pitch is regarded as 1. The unit of length in space when the servo track pitch is regarded as 1 is denoted by Svtrk.

[0062] exist Figure 4 In the example shown, the N pulse train and the Q pulse train each have a configuration in which the polarity is reversed every predetermined length in the circumferential direction. In the radial direction, the N pulse train and the Q pulse train each reverse the polarity every 1 Svtrk. Furthermore, the N pulse train is recorded so that the maximum amplitude is obtained at a position offset by 0.5 Svtrk from the center of the track. In addition, the Q pulse train is recorded so that the maximum amplitude is obtained at the center of the track.

[0063] RWC25 takes in a pulse train pattern (that is, each of the N pulse train and the Q pulse train) at a sampling interval based on the servo clock. RWC25 performs a discrete Fourier transform (DFT) process on the pulse train sampling waveform thus obtained, for example, to obtain the sine (sin) component and cosine (cos) component of the pulse train frequency, or the phase and amplitude. Here, as an example, it is assumed that RWC25 obtains the phase and amplitude for explanation. In the following, the phase and amplitude of the pulse train frequency obtained by performing DFT processing on the pulse train sampling waveform are sometimes referred to as the phase and amplitude of the demodulated signal of the pulse train pattern.

[0064] The SoC 30 (eg, the processor 26) calculates a burst offset based on the phase and amplitude of the demodulated signal of the burst pattern. The burst offset is the offset from one servo track 41. The SoC 30 calculates the radial position of the head 22 based on the cylinder address and the burst offset.

[0065] Return the description Figure 3 .

[0066] Regarding the shape of the tracks (data tracks and servo tracks 41), a perfect circle is an ideal shape. However, due to vibrations when writing servo data, servo pattern quality, etc., the servo track 41 is deformed. As a result, there is a situation where the radial position (radial position) of the servo track 41 determined based on the combination of the cylinder address and the pulse train offset deviates from the radial position of the servo track 41 of the ideal shape. This position deviation occurs repeatedly in the same manner with one rotation of the disk 11 (and SPM 12), so it is called RRO (Repeatable RunOut). The post-code is a code obtained by encoding the correction amount of the RRO.

[0067] The SoC 30 (e.g., the processor 26) corrects the radial position of the magnetic head 22 obtained from the combination of the cylinder address and the burst offset using the RRO correction amount recorded as the post-code, thereby obtaining the radial position of the magnetic head 22 in which the position deviation based on the RRO is eliminated. The correction using the RRO correction amount is referred to as RRO correction.

[0068] Figure 5 This is a diagram for explaining an example of a method for learning the RRO correction amount.

[0069] In the manufacturing process of the magnetic disk device 1, after writing the Gray code and / or the burst pattern, the RRO correction amount is learned. In the process of learning the RRO correction amount, a plurality of servo tracks 41 or data tracks are sequentially set as target tracks, and for each target track, the difference between the actual radial position of the magnetic head 22 and the radial position of the target track is measured under positioning control based on the Gray code and the burst pattern.

[0070] That is, the SoC 30 reads the Gray code and the pulse train pattern by the reading head 22r, and estimates the position of the magnetic head 22 based on the read Gray code and the pulse train pattern. Moreover, the SoC 30 positions the magnetic head 22 on the target track based on the estimated position of the magnetic head 22. Meanwhile, the SoC 30 obtains the deviation amount of the estimated position of the magnetic head 22 from the target track as the RRO correction amount.

[0071] Figure 5 The dotted line shown is the track that the head 22 passes through, observed under the control of being positioned at a certain target track in the process of learning the RRO correction amount. For example, the SoC 30 obtains the position of the head 22 whenever the head 22 passes through the servo sector SV. Thus, as shown in this figure, the observed track has a shape such as a broken line. The SoC 30 obtains the deviation of the position of the head 22 in each servo sector SV from the radial direction of the target track as the RRO correction amount in each servo sector SV. The SoC 30 records each RRO correction amount as a post-code in the corresponding servo sector SV.

[0072] In addition, use Figure 5 The above-described method of learning the RRO correction amount is merely an example, and the method of calculating the RRO correction amount in each servo sector SV based on the observed trajectory can be modified in various ways.

[0073] Hereinafter, the phase and amplitude of the demodulated signal of the pulse train pattern obtained by demodulating the pulse train pattern are recorded as a pulse train demodulation value set. The pulse train demodulation value set includes the phase and amplitude of the demodulated signal of the N pulse train and the phase and amplitude of the demodulated signal of the Q pulse train.

[0074] The estimated position of the magnetic head 22 obtained by adding the cylinder address and the burst offset is recorded as the first servo demodulation position. The first servo demodulation position after RRO correction, which is the estimated position of the magnetic head 22 used for positioning, is recorded as the second servo demodulation position.

[0075] As an example of a method for increasing the storage capacity of a magnetic disk device, there can be cited an example of reducing the radial spacing of data tracks, that is, the track pitch of data tracks as much as possible. If the position error between the magnetic head and the target track (hereinafter, the position error is assumed to be a position error RPE (Repeatable Position Error) synchronized with the rotation and excluding NRPE (Non Repeatable Position Error)) can be minimized by controlling the position of the magnetic head so that the magnetic head does not follow the RRO, the track pitch of the data track can be reduced and the storage capacity of the magnetic disk device can be increased. In the case where the RRO can be completely corrected, the error RPE between the position of the magnetic head and the target track can be set to 0. As a result, multiple data tracks can be set at equal intervals in the radial direction without setting a margin for compensating data in consideration of the position error RPE, and the capacity loss caused by the position error RPE can be set to 0.

[0076] Here, the observed position error RPE may be different depending on whether it is in a writing action or a non-writing action.

[0077] The write operation is an operation of writing data to a data sector while positioning the magnetic head 22. That is, in the write operation, when the magnetic head 22 passes through a servo sector SV, the servo sector SV is read, and when the magnetic head 22 passes through a data sector, data is written to the data sector.

[0078] The non-write operation is an operation that positions the magnetic head 22 but does not write data to a data sector. Various operations belong to the non-write operation.

[0079] For example, a read action of reading data from a data sector belongs to a non-write action. In the read action, when the magnetic head 22 passes through the servo sector SV, the servo sector SV is read, and when the magnetic head 22 passes through the target data sector, data is read from the target data sector.

[0080] In addition, when the SoC 30 starts the write operation, it performs a seek operation to move the magnetic head 22 to the target data track, and positions the magnetic head 22 on the target data track. When the magnetic head 22 is positioned on the target data track, and the magnetic head 22 reaches one of the target data sectors, the SoC 30 starts the write operation. Part or all of the actions accompanying the positioning before the start of the write operation belong to non-write operations.

[0081] For example, as a technology for realizing high-quality writing, known DFH (Dynamic Flying Height) technology is provided. According to the DFH technology, the floating amount (Flying Height) of the magnetic head can be adjusted. And, during the write action, the floating amount of the magnetic head is controlled to a predetermined small value. Specifically, before the write action begins, the control of making the floating amount of the magnetic head become a predetermined small value is first started, and then the write action is started. The action from controlling the floating amount of the magnetic head to a predetermined small value to starting the write action belongs to a non-write action.

[0082] In the above-mentioned process of learning the RRO correction amount, no data is written in the operation of reading servo data from each servo sector SV. That is, in the above-mentioned process of learning the RRO correction amount, the operation of positioning the magnetic head 22 is a non-write operation.

[0083] Figure 6 1 is a diagram showing an example of position error RPE observed in a write action and a non-write action. In this figure, the position error RPE observed in each action when the magnetic head 22 is positioned at the data track #M among the three data tracks (data track #M-1, data track #M, data track #M+1) arranged in the radial direction is depicted. As shown in this figure, it can be seen that the position error RPE observed in the write action is worse than the position error RPE observed in the non-write action.

[0084] The reason why the position error RPE observed in the write action is worse than the position error RPE observed in the non-write action is as follows. That is, this is because, when the servo demodulation position calculated based on the pulse train demodulation value set in the write action is corrected using the RRO correction amount calculated based on the pulse train demodulation value set in the non-write action, the RRO correction value is sometimes inappropriate. The reason why the RRO correction value becomes inappropriate is that the pulse train demodulation value set in the write action is sometimes different from the pulse train demodulation value set in the non-write action. The servo demodulation position is the result calculated based on a predetermined calculation formula for a certain pulse train demodulation value set, so a change in the pulse train demodulation value set means that the servo demodulation position will change. In other words, the RRO looks different. The reason why the pulse train demodulation value set is different in the write action and the non-write action is that the transient response when changing from the state of writing data to the state of reading servo data (the floating amount of the head, the temperature, the leakage magnetic field from the write head, and the time used to stabilize the read output) affects the reading of the pulse train waveform.

[0085] In the embodiment, the SoC 30 corrects the pulse train demodulation value set obtained in the write operation to make it close to the pulse train demodulation value set obtained in the non-write operation, thereby suppressing the deterioration of the position error RPE in the write operation.

[0086] In the following, a pulse string demodulation value set obtained by positioning control in a non-write action is sometimes recorded as a pulse string demodulation value set in a non-write action, and a pulse string demodulation value set obtained by positioning control in a write action is sometimes recorded as a pulse string demodulation value set in a write action.

[0087] Figure 7 It is a schematic diagram showing an example of a functional configuration related to positioning control of the magnetic disk device 1 according to the embodiment.

[0088] The RWC 25 includes a Gray code demodulation unit 251 and a pulse train demodulation unit 252. The processor 26 functions as a first correction unit 261, a second correction unit 262, a third correction unit 263, and a correction setting information generation unit 264 based on a firmware program.

[0089] The servo waveform is input to the RWC 25 from the preamplifier 24 .

[0090] The Gray code demodulation unit 251 obtains the cylinder address by decoding the Gray code waveform included in the input servo waveform. The burst demodulation unit 252 obtains a burst demodulation value set by demodulating the burst waveform included in the input servo waveform, that is, performing DFT processing.

[0091] In the case of a write operation, the first correction unit 261 corrects the burst demodulation value set to be close to the burst demodulation value set in the non-write operation using the pre-generated correction setting information 300. The first correction unit 261 outputs the corrected burst demodulation value set to the second correction unit 262.

[0092] When the writing operation is not in progress, the first correction unit 261 does not correct the burst demodulation value set, but outputs the burst demodulation value set to the second correction unit 262 .

[0093] The second correction unit 262 calculates a burst offset based on the input burst demodulation value set. The burst offset is added to the cylinder address to obtain a first servo demodulation position.

[0094] The third correction unit 263 performs correction based on the RRO correction amount on the first servo demodulation position to obtain a second servo demodulation position, and outputs the second servo demodulation position.

[0095] The correction setting information generating unit 264 generates the correction setting information 300. The correction setting information 300 is numerical information used as an argument of a correction algorithm for making the pulse train demodulation value set obtained in the write operation close to the pulse train demodulation value set in the non-write operation. Details of the correction setting information 300 and the correction algorithm will be described later.

[0096] The correction setting information 300 generated by the correction setting information generating unit 264 is stored in a predetermined memory. Here, as an example, it is assumed that the storage destination memory of the correction setting information 300 is FROM28. The storage destination memory of the correction setting information 300 is not limited to this. The correction setting information 300 can also be stored in the system area set in the magnetic disk 11, and can also be stored in each servo sector SV. The correction setting information 300 can also be stored in a non-volatile memory that is different from both the magnetic disk 11 and FROM28. In addition, during operation, the correction setting information 300 can also be loaded into DRAM29, and the processor 26 can also use the correction setting information 300 loaded into DRAM29.

[0097] In addition, the first correction unit 261, the second correction unit 262, the third correction unit 263, and the correction setting information generation unit 264 are described as being implemented by the processor 26. Some or all of these functional components may be implemented by hardware circuits such as FPGA or ASIC. In addition, some or all of these functional components may be provided by an integrated circuit other than the processor 26, such as the RWC 25.

[0098] Next, the operation details of the magnetic disk device 1 according to the embodiment and the processing details of several functional components will be described.

[0099] Figure 8 1 is a flowchart showing an example of the generation action of the correction setting information 300 of the embodiment. Here, an example of generating the correction setting information 300 related to a certain servo sector SV (recorded as the object servo sector SV) is described. In addition, the series of processes shown in this figure are executed after the learning and recording of the RRO are completed in the manufacturing process, for example. In addition, the execution timing of these series of processes is not limited to this. These series of processes can also be executed after the magnetic disk device 1 is shipped.

[0100] First, the correction setting information generating unit 264 performs a non-write operation on the servo track 41 or the data track including the target servo sector SV, and obtains a pulse train demodulation value set in the non-write operation related to the target servo sector SV (S101). Specifically, the correction setting information generating unit 264 does not write to the data area DA, but positions the magnetic head 22 while demodulating the pulse train pattern in the positioning, and obtains a pulse train demodulation value set obtained by demodulation as a pulse train demodulation value set in the non-write operation. In the pulse train demodulation value set in the non-write operation obtained by the process of S101, the amplitude of the demodulation signal of the N pulse train is recorded as Namp0, the phase of the demodulation signal of the N pulse train is recorded as Nphs0, the amplitude of the demodulation signal of the Q pulse train is recorded as Qamp0, and the phase of the demodulation signal of the Q pulse train is recorded as Qphs0.

[0101] Next, the correction setting information generating unit 264 performs a write operation on the servo track 41 or the data track including the target servo sector SV, and obtains a pulse train demodulation value set in the write operation related to the target servo sector SV (S102). Specifically, the correction setting information generating unit 264 performs writing to the data area DA, and while positioning the magnetic head 22, demodulates the pulse train pattern in the positioning, and obtains a pulse train demodulation value set obtained by demodulation as a pulse train demodulation value set in the write operation. In the pulse train demodulation value set in the write operation obtained by the process of S102, the amplitude of the demodulation signal of the N pulse train is recorded as Namp1, the phase of the demodulation signal of the N pulse train is recorded as Nphs1, the amplitude of the demodulation signal of the Q pulse train is recorded as Qamp1, and the phase of the demodulation signal of the Q pulse train is recorded as Qphs1.

[0102] Next, the correction setting information generating section 264 calculates the correction setting information 300 related to the target servo sector SV (S103). The correction setting information generating section 264 calculates the correction setting information 300 based on the following equations 1 to 4.

[0103] Ngain = Namp0 / Namp1 (Formula 1)

[0104] Qgain = Qamp0 / Qamp1 (Formula 2)

[0105] Nphsofs=Nphs0-Nphs1 (Formula 3)

[0106] Qphsofs=Qphs0-Qphs1 (Formula 4)

[0107] In this example, the correction setting information 300 is a set of the amplitude ratio Ngain of the demodulated signal of the N pulse string, the amplitude ratio Qgain of the demodulated signal of the Q pulse string, the phase difference Nphsofs of the demodulated signal of the N pulse string, and the phase difference Qphsofs of the demodulated signal of the Q pulse string.

[0108] Next, the correction setting information generating section 264 stores the correction setting information 300 obtained by the calculation in the FROM 28 (S104). Then, the operation of generating the correction setting information 300 related to the target servo sector SV is completed.

[0109] also, Figure 8 The series of processing shown is executed, for example, for each of a plurality of servo sectors SV of the magnetic disk 11. In that case, the correction setting information 300 is generated and stored for each servo sector SV.

[0110] One correction setting information 300 is used for positioning in one corresponding servo sector SV. However, one correction setting information 300 may also be shared by a plurality of servo sectors SV.

[0111] For example, the correction setting information generating section 264 averages the pulse train demodulation value set in the non-write operation and the pulse train demodulation value set in the write operation in the group of servo sector SVs, and calculates the correction setting information 300 based on the pulse train demodulation value set in the non-write operation averaged in the group of servo sector SVs and the pulse train demodulation value set in the write operation averaged in the group of servo sector SVs. Then, the first correction section 261 uses the correction setting information 300 generated from the group of servo sector SVs in positioning within any servo sector SV in the group of servo sector SVs.

[0112] Alternatively, the correction setting information generating unit 264 performs the processes of S101 to S104 for each servo sector SV. Then, the correction setting information generating unit 264 averages the correction setting information 300 generated for each servo sector SV in the group of servo sector SVs. Furthermore, the first correction unit 261 uses the correction setting information 300 averaged in the group of servo sector SVs in positioning in any servo sector SV in the group of servo sector SVs.

[0113] In this way, by sharing one correction setting information 300 in a group of servo sectors SV, it is possible to reduce the capacity for storing the correction setting information 300 and reduce the time required to read the correction setting information 300 when performing positioning.

[0114] The method for determining the group of servo sector SVs that share one correction setting information 300 is arbitrary. All servo sector SVs included in one servo track 41 or data track may share one correction setting information 300. Alternatively, the recording surface of the magnetic disk 11 may be divided into a plurality of partitions arranged in the radial direction, and all servo sector SVs included in each partition may share one correction setting information 300.

[0115] That is, the correction setting information generating unit 264 may calculate a correction setting information 300 for every two or more servo sectors SV and store it in FROM28, or may calculate a correction setting information 300 for every two or more servo tracks 41 or data tracks and store it in FROM28.

[0116] Fig. 9 Here, the operation when the magnetic head 22 passes through a certain servo sector SV in the non-writing operation will be described.

[0117] First, the Gray code demodulation unit 251 obtains the cylinder address (S201). Next, the pulse train demodulation unit 252 obtains a pulse train demodulation value set (S202). In the obtained pulse train demodulation value set, the amplitude of the demodulation signal of the N pulse train is recorded as Namp, the phase of the demodulation signal of the N pulse train is recorded as Nphs, the amplitude of the demodulation signal of the Q pulse train is recorded as Qamp, and the phase of the demodulation signal of the Q pulse train is recorded as Qphs.

[0118] The first correction unit 261 outputs the pulse train demodulation value set acquired by the process of S202 to the second correction unit 262 .

[0119] The second correction unit 262 calculates a burst offset based on the input burst demodulation value set, that is, the set of Namp, Nphs, Qamp, and Qphs (S203).

[0120] The algorithm used by the second correction unit 262 to calculate the burst offset based on the burst demodulation value set is arbitrary. An example of the algorithm used to calculate the burst offset based on the burst demodulation value set will be described below.

[0121] The second correction unit 262 calculates the burst offset BstPos1 by using the following equations 5 to 10. In this specification, "*" is an operator that means multiplication.

[0122] Nbst1=Namp*sin(Nphs+PhsCmp) (Formula 5)

[0123] Qbst1=Qamp*sin(Qphs+PhsCmp) (Formula 6)

[0124] Nbst2=cos(AzmCmp)*Nbst1-sin(AzmCmp)*Qbst1 (Formula 7)

[0125] Qbst2=sin(AzmCmp)*Nbst1+cos(AzmCmp)*Qbst1 (Formula 8)

[0126] BstPos0=arctan(Qbst2 / Nbst2) (Formula 9)

[0127] BstPos1=BstPos0+TableCmp (Formula 10)

[0128] The processing represented by equations 5 and 6 is called initial phase correction. PhsCmp is the correction value of the initial phase correction, that is, the initial phase correction value. The initial phase correction value is adjusted to maximize the amplitudes Namp and Qamp in the pulse train demodulation value set. Nbst1 and Qbst1 are the pulse train data after the initial phase correction.

[0129] The processing represented by equations 7 and 8 is called rotation correction. AzmCmp is a value for correcting the pulse train data after the initial phase correction, and is a rotation correction value. Nbst2 and Qbst2 are the pulse train data after the rotation correction.

[0130] Formula 9 represents the process of calculating the phase angle represented by the points of the rotation-corrected pulse train data Nbst2 and Qbst2 when the horizontal axis is the N pulse train data axis and the vertical axis is the Q pulse train data axis. Since a phase angle of 360 degrees is equivalent to a distance of 2Svtrk, it can be considered that the phase obtained by Formula 9 represents a pulse train offset. The phase obtained by Formula 9 is recorded as a pulse train offset BstPos0. In addition, a phase angle of ±180 degrees can be calculated as a pulse train offset of ±1Svtrk.

[0131] Formula 10 is a calculation for correcting a portion of the deviation of the pulse train offset from the target track, which is called table correction. TableCmp is a table correction value adjusted for the pulse train offset BstPos0 calculated by Formula 9. BstPos1 calculated by Formula 10 is the pulse train offset after the table correction. The second correction unit 262 outputs the pulse train offset BstPos1.

[0132] The processor 26 adds the burst offset BstPos1 to the cylinder address obtained by the Gray code demodulation unit 251. The third correction unit 263 performs RRO correction on the first servo demodulation position obtained by adding the burst offset BstPos1 to the cylinder address (S204). By performing RRO correction on the first servo demodulation position, a second servo demodulation position is obtained.

[0133] The processor 26 uses the second servo demodulation position as the current position of the magnetic head 22, and performs positioning (S205) to make the magnetic head 22 close to the target data track. Then, the action when the magnetic head 22 passes through a certain servo sector SV in the non-write action ends. In the non-write action, the SoC 30 can position the magnetic head 22 on the target data track by repeatedly performing the processing of S201 to S205.

[0134] Fig.10 Here, the operation when the magnetic head 22 passes through a certain servo sector SV during the write operation will be described.

[0135] First, the Gray code demodulation unit 251 obtains the cylinder address (S301). Next, the pulse train demodulation unit 252 obtains a pulse train demodulation value set (S302). In the obtained pulse train demodulation value set, the amplitude of the demodulation signal of the N pulse train is recorded as Nampw, the phase of the demodulation signal of the N pulse train is recorded as Nphsw, the amplitude of the demodulation signal of the Q pulse train is recorded as Qampw, and the phase of the demodulation signal of the Q pulse train is recorded as Qphsw.

[0136] The first correction unit 261 obtains the correction setting information 300, that is, the set of Ngain, Qgain, Nphsofs, and Qphsofs (S303). Then, the first correction unit 261 uses the correction setting information 300 as an argument of the correction algorithm to correct the pulse train demodulation value set, that is, the set of Nampw, Nphsw, Qampw, and Qphsw (S304). The first correction unit 261 corrects the pulse train demodulation value set by using the correction algorithm shown in the following equations 11 to 14.

[0137] Nampc = Ngain * Nampw (Formula 11)

[0138] Qampc=Qgain*Qampw (Equation 12)

[0139] Nphsc=Nphsw+Nphsofs (Formula 13)

[0140] Qphsc=Qphsw+Qphsofs (Equation 14)

[0141] Nampc is the amplitude Nampw of the demodulated signal of the modified N pulse train. Qampc is the amplitude Qampw of the demodulated signal of the modified Q pulse train. Nphsc is the phase Nphsw of the demodulated signal of the modified N pulse train. Qphsc is the phase Qphsw of the demodulated signal of the modified Q pulse train.

[0142] The first correction unit 261 outputs the corrected pulse train demodulation value set acquired by the process of S304 to the second correction unit 262 .

[0143] The second correction unit 262 calculates the burst offset based on the input burst demodulation value set, that is, the set of Nampc, Nphsc, Qampc and Qphsc (S305). Fig. 9 The pulse train offset BstPos1 is calculated using the same algorithm as that used in the process of S203 shown.

[0144] The processor 26 adds the burst offset BstPos1 to the cylinder address obtained by the Gray code demodulation unit 251. The third correction unit 263 performs RRO correction on the first servo demodulation position obtained by adding the burst offset BstPos1 to the cylinder address (S306). By performing RRO correction on the first servo demodulation position, a second servo demodulation position is obtained.

[0145] The processor 26 uses the second servo demodulation position as the current position of the magnetic head 22, and performs positioning (S307) to make the magnetic head 22 close to the target data track. Then, the action when the magnetic head 22 passes through a certain servo sector SV in the write operation ends. In the write operation, the SoC 30 can position the magnetic head 22 on the target data track by repeatedly performing the processing of S301 to S307.

[0146] Next, a more specific example of the correction setting information 300 and the effect of correction using the correction setting information 300 will be described.

[0147] Fig.11 Yes means through Figure 8 The figure shows an example of the amplitude Namp0 of the demodulated signal of the N pulse train and the amplitude Qamp0 of the demodulated signal of the Q pulse train in the pulse train demodulation value set obtained in the process of S101 in the non-write operation. In this figure, the horizontal axis represents the radial offset from a certain servo track 41, and the vertical axis represents the amplitude.

[0148] Fig.12 Yes means through Figure 8 The figure shows an example of the phase Nphs0 of the demodulated signal of the N pulse train and the phase Qphs0 of the demodulated signal of the Q pulse train in the pulse train demodulation value set obtained in the process of S101 in the non-write operation. In this figure, the horizontal axis represents the radial offset from a certain servo track 41, and the vertical axis represents the phase.

[0149] Fig.13 Yes means through Figure 8 The figure shows an example of the amplitude Namp1 of the demodulated signal of the N pulse train and the amplitude Qamp1 of the demodulated signal of the Q pulse train in the pulse train demodulation value set obtained in the process of S102 in the write operation. In this figure, the horizontal axis represents the radial offset from a certain servo track 41, and the vertical axis represents the amplitude.

[0150] Fig.14 Yes means through Figure 8 The figure shows an example of the phase Nphs1 of the demodulated signal of the N pulse train and the phase Qphs1 of the demodulated signal of the Q pulse train in the pulse train demodulation value set obtained in the process of S102 in the write operation. In this figure, the horizontal axis represents the radial offset from a certain servo track 41, and the vertical axis represents the phase.

[0151] right Fig.11 and Fig.13 By comparison, it can be seen that the amplitude is slightly different in non-writing action and writing action. Fig.12 and Fig.14 By comparison, it can be seen that the phase is slightly different in the non-writing action and the writing action.

[0152] Fig.15 This is a graph obtained by plotting the initial phase-corrected pulse train data Nbst1, Qbst1 calculated based on the pulse train demodulation value set in the non-write action and the initial phase-corrected pulse train data Nbst1, Qbst1 calculated based on the pulse train demodulation value set in the write action without using the correction setting information 300 on a two-dimensional plane. The horizontal axis of the graph is the N pulse train data axis, and the vertical axis is the Q pulse train data axis. The waveform plotted on such a graph is also called a Lissajous waveform. As shown in this figure, it can be seen that the initial phase-corrected pulse train data Nbst1, Qbst1 calculated based on the pulse train demodulation value set in the non-write action are inconsistent with the initial phase-corrected pulse train data Nbst1, Qbst1 calculated based on the pulse train demodulation value set in the write action without using the correction setting information 300.

[0153] Fig.16 Yes means through Figure 8 1 is a diagram showing an example of the amplitude ratio Ngain and Qgain in the correction setting information 300 obtained by the process of S103 shown in FIG. In this figure, the horizontal axis represents the offset in the radial direction from a certain servo track 41, and the vertical axis represents the magnitude of the amplitude ratio. If the amplitude is equal in the non-write action and the write action, the amplitude ratio should be 1. However, in reality, the amplitude is slightly different in the non-write action and the write action, so as shown in this figure, the amplitude ratio deviates slightly from 1.

[0154] Fig.17 Yes means through Figure 8 103 is a diagram showing an example of the phase difference Nphsofs, Qphsofs in the correction setting information 300 obtained by the process of S103 shown in FIG. In this figure, the horizontal axis represents the offset in the radial direction from a certain servo track 41, and the vertical axis represents the magnitude of the phase difference. If the phases in the non-write action and the write action are equal, the phase difference should be 0. However, in reality, the phases in the non-write action and the write action are slightly different, so as shown in this figure, the phase difference deviates slightly from 0.

[0155] Fig.18This is a diagram showing an example of observing the difference between the second servo demodulation position calculated based on the burst demodulation value set in the non-writing operation and the second servo demodulation position calculated based on the burst demodulation value set in the writing operation without correction using the correction setting information 300 in a plurality of servo sectors SV on a certain servo track 41 or a certain data track. As can be seen from this figure, since the difference between the burst demodulation value set in the non-writing operation and the burst demodulation value set in the writing operation is not eliminated, a difference occurs between the second servo demodulation positions.

[0156] Fig.19 This is a diagram showing an example of observing the difference between the second servo demodulation position calculated based on the burst demodulation value set in the non-writing operation and the second servo demodulation position calculated by correcting the burst demodulation value set in the writing operation using the correction setting information 300 in a plurality of servo sectors SV on a certain servo track 41 or a certain data track. As can be seen from this figure, the burst demodulation value set in the writing operation is corrected using the correction setting information 300, and as a result, the difference between the second servo demodulation position in the non-writing operation and the second servo demodulation position in the writing operation is greatly suppressed.

[0157] As described above, the RRO correction amount recorded as a post-code is learned in the non-write action. That is, if the RRO correction is performed in the non-write action, the error based on RRO between the target track and the position of the head 22 can be most effectively suppressed. According to the embodiment, since the difference between the second servo demodulation position in the non-write action and the second servo demodulation position in the write action can be greatly suppressed, the error based on RRO can be effectively suppressed in the write action as in the non-write action. That is to say, the error between the target track and the position of the head in the write action can be suppressed. As a result, the designer can reduce the data track spacing and increase the storage capacity of the magnetic disk device 1.

[0158] As described above, according to the embodiment, in the write operation, that is, the operation of writing to the data area DA while positioning the magnetic head 22, the SoC 30 operates as follows. That is, the SoC 30 demodulates the pulse train pattern to obtain a pulse train demodulation value set. Furthermore, the SoC 30 corrects the pulse train demodulation value set based on a correction algorithm using the correction setting information 300 as an independent variable. Furthermore, the SoC 30 calculates the pulse train offset based on the corrected pulse train demodulation value set.

[0159] Since the pulse train demodulation value set in the write operation can be made close to the pulse train demodulation value set in the non-write operation, the deterioration of the position error RPE in the write operation can be suppressed. As a result, the designer can reduce the data track pitch and increase the storage capacity of the magnetic disk device 1.

[0160] In addition, in a non-write action, that is, an action of positioning the head 22 but not writing to the data area DA, SoC30 demodulates the pulse string pattern to obtain a pulse string demodulation value set, does not correct the pulse string demodulation value set, and calculates the pulse string offset based on the pulse string demodulation value set.

[0161] In addition, according to the embodiment, if using Figure 8 As described above, the SoC 30 does not write to the data area DA, but positions the magnetic head 22 while demodulating the pulse train pattern in the positioning to obtain a pulse train demodulation value set in the non-write operation. The SoC 30 writes to the data area DA, and positions the magnetic head 22 while demodulating the pulse train pattern in the positioning to obtain a pulse train demodulation value in the write operation. Moreover, the SoC 30 calculates the correction setting information 300 based on the pulse train demodulation value set in the non-write operation and the pulse train demodulation value set in the write operation, and stores the correction setting information 300 in the memory (for example, FROM 28).

[0162] Thus, in the write operation, the burst demodulation value set output from the burst demodulation unit 252 can be corrected based on the correction setting information 300 prepared in advance so as to be close to the burst demodulation value set in the non-write operation.

[0163] According to the embodiment, the servo data includes a post code indicating an RRO correction amount. The RRO correction amount is obtained without writing while positioning the magnetic head 22. The SoC 30 further performs correction based on the post code during positioning of the magnetic head 22.

[0164] As a result, the RRO can be appropriately corrected in the non-write operation. As described above, in the write operation, the pulse train demodulation value set output from the pulse train demodulation unit 252 can be corrected to be close to the pulse train demodulation value set in the non-write operation. As a result, in the write operation, the RRO can be appropriately corrected as in the non-write operation.

[0165] In addition, as described above, in the embodiment, the SoC 30 may calculate the correction setting information 300 for each of the plurality of servo sectors and store it in the memory. Alternatively, the SoC 30 may calculate the correction setting information 300 for every two or more servo sectors SV among the plurality of servo sectors SV or every two or more servo tracks 41 among the plurality of servo tracks 41 and store it in the memory.

[0166] In addition, according to the embodiment, the following settings are made: the pulse train demodulation value set includes the amplitude and phase of the demodulated signal of the pulse train pattern, the correction setting information 300 includes the amplitude ratio Ngain, Qgain multiplied by the amplitude and the phase difference Nphsofs, Qphsofs added or subtracted from the phase, and the correction algorithm is an algorithm for correcting the amplitude and phase included in the pulse train demodulation value set based on the correction setting information 300. The SoC 30 may be configured to correct only one of the amplitude and phase included in the pulse train demodulation value set in the write operation.

[0167] For example, when SoC 30 is configured to correct only the amplitude of the amplitude and phase included in the pulse train demodulation value set, the correction setting information 300 is configured to include the amplitude ratio (that is, Ngain and Qgain) but not the phase difference (that is, Nphsofs and Qphsofs). Then, SoC 30 corrects the amplitude included in the pulse train demodulation value set based on the amplitude ratio (that is, Ngain and Qgain) included in the correction setting information 300 and the correction algorithm shown in equations 11 and 12.

[0168] In another example, when the SoC 30 is configured to correct only the phase of the amplitude and the phase included in the pulse train demodulation value set, the correction setting information 300 is configured to include the phase difference (that is, Nphsofs and Qphsofs) but not the amplitude ratio (that is, Ngain and Qgain). Then, the SoC 30 corrects the phase included in the pulse train demodulation value set based on the phase difference (that is, Nphsofs and Qphsofs) included in the correction setting information 300 and the correction algorithm shown in equations 13 and 14.

[0169] Fig. 20 This is a diagram showing an example of the difference between the second servo demodulation position calculated based on the pulse train demodulation value set in the non-write operation and the second servo demodulation position calculated by correcting only the amplitude based on the pulse train demodulation value set in the write operation, observed in a plurality of servo sectors SV on a certain servo track 41 or a certain data track. Fig.18 By comparison, it can be seen that even when only the amplitude is corrected, the difference between the second servo demodulation position in the non-writing operation and the second servo demodulation position in the writing operation can be suppressed.

[0170] Even when only the phase is corrected for the burst demodulation value set in the write operation, the difference between the second servo demodulation position in the non-write operation and the second servo demodulation position in the write operation can be suppressed.

[0171] Thus, the pulse train demodulation value set may include the amplitude and phase of the demodulated signal of the pulse train pattern, the correction setting information 300 may include the amplitude ratio or the phase difference, and the correction algorithm may correct the amplitude or phase included in the pulse train demodulation value set based on the correction setting information 300.

[0172] Several embodiments of the present invention have been described, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the invention. These embodiments and / or their variations are included in the scope and spirit of the invention, and are included in the invention described in the claims and the scope of their equivalents.

Claims

1. A magnetic disk device comprising: A magnetic disk having a plurality of servo tracks, on which a plurality of servo sectors each recording servo data including a burst pattern are arranged at intervals in a circumferential direction, and a data area for writing data is arranged between the servo sectors arranged in the circumferential direction; a magnetic head that performs writing and reading on the magnetic disk; a memory storing a first setting value; and A controller which, in a first action of positioning the magnetic head while writing to the data area, demodulates the pulse string pattern to obtain a first pulse string demodulation value, corrects the first pulse string demodulation value based on a correction algorithm using the first set value as an independent variable, and calculates an offset of the magnetic head from one of the plurality of servo tracks based on a second pulse string demodulation value which is the corrected first pulse string demodulation value.

2. The magnetic disk device according to claim 1, The controller, in the second action of positioning the head but not writing to the data area, demodulates the pulse train pattern to obtain a third pulse train demodulation value, and calculates the offset of the head from one of the multiple servo tracks based on the third pulse train demodulation value.

3. The magnetic disk device according to claim 1 or 2, The controller attempts to position the magnetic head and demodulates the pulse train pattern to obtain a fourth pulse train demodulation value without writing to the data area, and attempts to position the magnetic head and demodulates the pulse train pattern to obtain a fifth pulse train demodulation value while writing to the data area, calculates the first set value based on the fourth pulse train demodulation value and the fifth pulse train demodulation value, and stores the first set value in the memory.

4. The magnetic disk device according to claim 3, The first pulse train demodulation value, the fourth pulse train demodulation value, and the fifth pulse train demodulation value each include an amplitude and a phase of a demodulated signal of the pulse train pattern. The first setting value is an amplitude ratio or a phase difference, The amplitude ratio is a ratio of the amplitude included in the fourth pulse train demodulation value to the amplitude included in the fifth pulse train demodulation value. The phase difference is a difference between a phase included in the fourth pulse train demodulation value and a phase included in the fifth pulse train demodulation value. The correction algorithm is an algorithm for correcting the amplitude or phase included in the first pulse train demodulation value based on the first setting value.

5. The magnetic disk device according to claim 1, The first pulse train demodulation value includes the amplitude and phase of the demodulated signal of the pulse train pattern. The first set value includes a set value to be multiplied by the amplitude or a set value to be added to or subtracted from the phase, The correction algorithm is an algorithm for correcting the amplitude or the phase based on the first setting value.

6. The magnetic disk device according to claim 1, The servo data further includes a postcode having correction data for correcting a repeatable runout (RRO), wherein the correction data for correcting the RRO is an RRO correction amount calculated based on data obtained by measuring the positioning of the magnetic head without writing to the data area. The controller further performs head positioning correction based on the RRO correction data obtained from the post-code in positioning the magnetic head.

7. The magnetic disk device according to claim 3, The controller calculates the first setting value for each of the plurality of servo sectors and stores the first setting value in the memory.

8. The magnetic disk device according to claim 3, The controller calculates a plurality of the first setting values ​​for every two or more servo sectors among the plurality of servo sectors or every two or more servo tracks among the plurality of servo tracks, and stores an average value of the plurality of the first setting values ​​in the memory.

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