Magnetic disk drive

Abstract

To provide a magnetic disk drive capable of suitable servo control. [Solution] The magnetic disk device comprises a magnetic head and a magnetic disk. Multiple servo regions, each containing multiple data fragments, are arranged at equal intervals in the circumferential direction on the magnetic disk, with servo data written to them in a circumferential direction. At multiple consecutive first radial positions, the recording frequency of the servo data differs for each first radial position. In each of the multiple servo regions, the first data fragment among the multiple data fragments is written to a first circumferential position where the circumferential movement time of the magnetic head, based on the timing when the magnetic head passes a reference position on the circumference, is aligned among the multiple first radial positions.

Description

Technical Field

[0001] This embodiment relates to a magnetic disk drive.

Background Art

[0002] Conventionally, servo data is written at a constant recording frequency regardless of the position in the radial direction of the magnetic disk, or is written at a constant recording frequency in each of a plurality of ranges obtained by dividing the magnetic disk in the radial direction. In contrast, in recent years, a CDS (Constant Density Servo) method has been developed as a servo data recording method. According to the CDS method, the recording frequency is gently changed with respect to the radial direction so that the recording frequency is higher on the outer diameter side than on the inner diameter side. As a result, compared with the conventional servo data recording method, the area of the region where the servo data is written is reduced, and the area of the region where the user data can be written is increased.

[0003] However, from the viewpoint of servo control, there is room for improvement in the CDS method.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment aims to provide a magnetic disk drive capable of performing suitable servo control.

Means for Solving the Problems

[0006] According to one embodiment, the magnetic disk device comprises a magnetic head and a magnetic disk. The magnetic disk has multiple servo regions arranged at equal intervals in the circumferential direction, each on which servo data, containing multiple data fragments, is written in a circumferential direction. At multiple consecutive first radial positions, the recording frequency of the servo data differs for each first radial position. In each of the multiple servo regions, the first data fragment among the multiple data fragments is written to a first circumferential position where the circumferential movement time of the magnetic head, relative to the timing when the magnetic head passes a reference position on the circumference, is aligned among the multiple first radial positions. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 shows an example of the configuration of a magnetic disk device according to the first embodiment. [Figure 2] Figure 2 shows an example of the configuration of a magnetic disk according to the first embodiment. [Figure 3] Figure 3 shows an example of the configuration of servo data according to the first embodiment. [Figure 4] Figure 4 shows an example of a reference position set on a magnetic disk according to the first embodiment. [Figure 5] Figure 5 shows an example of the relationship between the radial position and the recording frequency of servo data according to the first embodiment. [Figure 6] Figure 6 is a diagram illustrating the method for writing servo data according to the first embodiment. [Figure 7] Figure 7 is a diagram illustrating an example of a method for writing servo data according to the second embodiment. [Figure 8] Figure 8 is a diagram illustrating an example of a burst pattern lighting method according to the third embodiment. [Figure 9] Figure 9 illustrates another example of a burst pattern lighting method according to the third embodiment. [Figure 10]FIG. 10 is a diagram for explaining yet another example of a method for writing a burst pattern according to the third embodiment. [Figure 11] FIG. 11 is a diagram for explaining an example of a method for writing servo data according to the fourth embodiment. [Figure 12] FIG. 12 is a diagram showing another example of the shape of a servo area according to the fifth embodiment. [Figure 13] FIG. 13 is a diagram for explaining an example of a method for writing servo data according to the fifth embodiment. [Figure 14] FIG. 14 is a diagram for explaining another example of a method for writing servo data according to the fifth embodiment. [Figure 15] FIG. 15 is a diagram for explaining yet another example of a method for writing servo data according to the fifth embodiment. [Figure 16] FIG. 16 is a diagram for explaining yet another example of a method for writing servo data according to the fifth embodiment. [Figure 17] FIG. 17 is a diagram for explaining an example of a method for writing servo data according to the sixth embodiment. [Figure 18] FIG. 18 is a flowchart showing an example of a sync search operation according to the sixth embodiment. [Figure 19] FIG. 19 is a diagram for explaining an example of the radial length of a constant frequency region according to the sixth embodiment. [Figure 20] FIG. 20 is a diagram for explaining another example of a method for writing servo data according to the sixth embodiment. [Figure 21] FIG. 21 is a diagram for explaining the timing of writing servo data according to a comparative example. BEST MODE FOR CARRYING OUT THE INVENTION

[0008] Hereinafter, a magnetic disk device according to an embodiment will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited by these embodiments.

[0009] (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of a magnetic disk device 1 according to the first embodiment.

[0010] The magnetic disk device 1 is connected to a host 2. The magnetic disk device 1 can receive an access command such as a write command or a read command from the host 2.

[0011] The magnetic disk device 1 includes a magnetic disk 11 having a magnetic layer formed on its surface. The magnetic disk device 1 accesses the magnetic disk 11 according to an access command. The access includes writing data and reading data.

[0012] Writing and reading of data are performed by a magnetic head 22. Specifically, in addition to the magnetic disk 11, the magnetic disk device 1 includes a spindle motor (SPM) 12, a lamp 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.

[0013] The magnetic disk 11 is rotated at a predetermined rotational speed by the coaxially attached SPM 12.

[0014] 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.

[0015] The magnetic head 22 includes a write head 22w and a read head 22r. The magnetic head 22 writes data to the magnetic disk 11 using the write head 22w. The magnetic head 22 reads data to the magnetic disk 11 using the read head 22r. The magnetic head 22 is mounted on the tip of the actuator arm 15. The magnetic head 22 is moved radially across the magnetic disk 11 by a VCM 16 driven by an SVC 21. Note that either one or both of the write head 22w and the read head 22r on the magnetic head 22 may be provided in multiple quantities on a single magnetic head 22.

[0016] When the rotation of the magnetic disk 11 is stopped, the magnetic head 22 is moved onto the ramp 13. The ramp 13 holds the magnetic head 22 in a position away from the magnetic disk 11.

[0017] The preamplifier 24 is an integrated circuit that performs data writing and reading via the magnetic head 22. During a read operation, the preamplifier 24 amplifies the signal read by the magnetic head 22 from the magnetic disk 11 and outputs it, supplying it to the RWC 25. During a write operation, the preamplifier 24 amplifies the signal corresponding to the data to be written supplied from the RWC 25 and supplies it to the magnetic head 22.

[0018] DRAM29 is used as a buffer for data transferred to and from host 2. For example, DRAM29 is used to temporarily store data to be written or data read from magnetic disk 11.

[0019] Furthermore, DRAM 29 is used by the processor 26 as operating memory. DRAM 29 is used as an area where the firmware program is loaded and an area where various management data is temporarily stored.

[0020] HDC23 controls the transfer of data between it and host 2 via the I / F bus. HDC23 supplies the data to be written, received from host 2, to RWC25 via DRAM29. HDC23 receives the read data output from RWC25 via DRAM29 and transmits that read data to host 2.

[0021] The RWC25 modulates the data to be written, supplied from the HDC23, and provides it to the preamplifier 24. The RWC25 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 as digital data to the HDC23.

[0022] The processor 26 is, for example, a CPU (Central Processing Unit). FROM 28 and DRAM 29 are connected to the processor 26.

[0023] FROM28 stores the firmware program and various configuration information. The firmware program may also be stored on the magnetic disk 11.

[0024] The processor 26 controls the magnetic disk device 1 according to a firmware program stored in FROM 28 or the magnetic disk 11. For example, the processor 26 loads the firmware program from FROM 28 or the magnetic disk 11 into DRAM 29 and controls the SVC 21, preamplifier 24, RWC 25, HDC 23, etc., according to the firmware program loaded into DRAM 29.

[0025] Furthermore, some or all of the functions of the processor 26 may be implemented by hardware circuits such as FPGAs (Field-Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits).

[0026] The HDC23, RWC25, and processor 26 are configured as a single integrated circuit, a System-On-a-Chip (SoC) 30. The SoC 30 may also include other elements (e.g., FROM 28 or DRAM 29).

[0027] Figure 2 shows an example of the configuration of a magnetic disk 11 according to the first embodiment. Note that this figure also shows an example of the rotation direction of the magnetic disk 11. The magnetic head 22 moves relative to the magnetic disk 11 due to the rotation of the magnetic disk 11. Therefore, the write / read direction, i.e., the direction in which data is written or read by the magnetic head 22 along the circumferential direction, is opposite to the rotation direction of the magnetic disk 11.

[0028] In the radial direction, the direction from the edge of the magnetic disk 11 toward the center is the ID direction, and the direction from the center of the magnetic disk 11 toward the edge is the OD direction.

[0029] During the manufacturing process, servo data used to position the magnetic head 22 is written to the magnetic disk 11, for example, by a servo writer or by self-servo writing (SSW). As shown in Figure 2, as an example of the arrangement of servo areas to which servo data has been written, a plurality of servo areas SV are formed, arranged radially and at equal intervals in the circumferential direction. The space between two circumferentially consecutive servo areas SV is used as a data area DA to which data is written.

[0030] Multiple concentric servo tracks 41 are provided in the radial direction of the magnetic disk 11. Multiple concentric data tracks are provided above the area of ​​the magnetic disk 11 where the multiple servo tracks 41 are provided. Multiple data sectors are provided in the circumferential direction within the area demarcated by the data area DA on each data track. Data can be written to each data sector. The data that can be written to each data sector includes user data received from the host 2, metadata associated with the user data (e.g., error correction codes), system data, etc. The magnetic disk device 1 has a pre-established positional relationship between the multiple servo tracks 41 and the multiple data tracks, and performs positioning control to position the magnetic head 22 on the target data track based on the servo data written to the servo area SV. Positioning control includes seek operation, which is the operation of moving the magnetic head 22 radially toward the target data track, and tracking operation, which is the operation of maintaining the magnetic head 22 on the target data track.

[0031] Note that multiple servo tracks 41 may be used as multiple data tracks. For the sake of simplicity, in the following explanation, we will assume that multiple servo tracks 41 are used as multiple data tracks. A servo track 41 will be simply referred to as track 41. Each individual region of the servo area SV separated by each track 41 is also called a servo sector.

[0032] A position in the radial direction is referred to as the radial position. A position in the circumferential direction is referred to as the circumferential position.

[0033] Figure 3 shows an example of the configuration of servo data according to the first embodiment.

[0034] Here, we define the expression of positional relationships. In a case where there are two adjacent first and second regions along the write / read direction, and the magnetic head 22 passes through the first region immediately before the second region, the second region may be described as the region "after" the first region, or the first region may be described as the region "before" the second region. In addition, in the circumferential direction, the position where the magnetic head 22 first passes through a certain region may be described as the "beginning" of that region. In some cases, the beginning portion of the data written to a certain region may be described as the "beginning" of the data.

[0035] As shown in Figure 3, the servo data includes multiple types of servo data fragments. These multiple types of servo data fragments are the preamble PR, sync mark SN, Gray code GC, burst pattern BP1, and burst pattern BP2. In the servo region SV, the preamble PR, sync mark SN, Gray code GC, burst pattern BP1, and burst pattern BP2 are arranged in this order in the write / read direction.

[0036] The preamble PR is a single-period pattern data that changes periodically in the circumferential direction. The frequency of the preamble PR pattern data corresponds to the recording frequency of the servo data. The preamble PR is used to adjust the amplitude, phase, and frequency of the sampled data when the servo waveform read by the read head 22r is acquired as sampled data by the RWC25 based on the servo clock. The servo clock is generated by the RWC25. In other words, the preamble PR is used to make the servo clock correspond to the recording frequency of the servo data.

[0037] The sync mark SN is pattern data used to identify the read timing of servo data. The SoC30 identifies the read timing of various servo data fragments based on the detection timing of the sync mark SN and the count value of its own counter (not shown).

[0038] The Gray code GC includes a cylinder address for identifying each track 41 on the magnetic disk 11 and a sector address for identifying a servo sector on the track 41.

[0039] Burst pattern BP1 and burst pattern BP2 are pattern data used to detect the offset amount of the position of the magnetic head 22 from the track center of a certain servo track 41 (more precisely, the track 41 indicated by the cylinder address).

[0040] Each burst pattern is captured by the RWC25 at a sampling interval based on the servo clock. The RWC25 processes the waveform of each captured burst pattern, for example, by performing a Discrete Fourier Transform (DFT), thereby obtaining the phase and amplitude. Based on the phase and amplitude obtained by the RWC25, the SoC30 calculates the offset amount of the magnetic head 22 from the track center of track 41. The SoC30 (e.g., processor 26) estimates the radial position of the magnetic head 22 based on the cylinder address obtained from the Gray code GC and the offset amount obtained from each burst pattern.

[0041] Furthermore, servo data may include any other type of servo data fragments besides those mentioned above. For example, servo data may include a postcode indicating the amount of positional deviation correction based on RRO (Repeatable RunOut).

[0042] A reference position is set at a point on the circumference of the magnetic disk 11. Multiple servo sectors, which are arranged at equal intervals in the circumferential direction, are given numerical information as sector addresses in ascending order based on the reference position.

[0043] A servo sector is a region of the servo area SV delimited by track 41. Therefore, the servo addresses of each servo sector included in a single servo area SV are the same. Hereafter, a servo area SV consisting of a servo sector with sector address i may be referred to as servo area SV#i.

[0044] Figure 4 shows an example of a reference position set on the magnetic disk 11 according to the first embodiment.

[0045] In the example shown in Figure 4, a reference position line is provided that extends straight in the radial direction. The shape of the reference position line does not necessarily have to be straight. For example, the reference position line may have a curved shape depending on the path along which the magnetic head 22 is moved by the VCM 16.

[0046] In the first embodiment, the servo data is recorded using the CDS method. According to the CDS method, as shown in Figure 5, the recording frequency of the servo data is smoothly changed in the radial direction such that the recording frequency is higher on the outer circumference than on the inner circumference.

[0047] As mentioned above, the magnetic disk 11 is rotated at a constant rotational speed. Therefore, the relative movement speed of the magnetic head 22 with respect to the magnetic disk 11 in the circumferential direction increases as it approaches the outer edge. Thus, assuming that the recording frequency is constant in the radial direction, the circumferential length of the servo sector increases as it approaches the outer edge.

[0048] In contrast, with the ODS method, the recording density of servo data is higher on the outer circumference than on the inner circumference, thus suppressing the increase in the circumferential length of the servo sector as it approaches the outer circumference. As a result, as shown in Figure 2, for example, the circumferential width of each servo region SV can be kept constant regardless of the radial position. Therefore, compared to the case where the recording frequency is constant in the radial direction, the area of ​​the region where user data can be recorded, i.e., the data region DA, increases.

[0049] In the example shown in Figure 2, each servo region SV has a shape that extends straight from the inner circumference to the outer circumference. However, the shape of each servo region SV is not limited to this. Each servo region SV may have a curved shape.

[0050] This section describes technologies that are comparable to the embodiments. Technologies that are comparable to the embodiments are referred to as comparative examples. According to the comparative example, servo data is written using the ODS method. The timing of writing the servo data is determined by a count using a servo clock (or a frequency divider clock) adjusted to a frequency corresponding to the recording frequency. Servo data is recorded when the count value of the servo clock (or a frequency divider clock) reaches a common value regardless of the radial position. This forms each servo region SV that extends in the radial direction.

[0051] Figure 21 is a diagram illustrating the timing of servo data writing for a comparative example. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis. In this specification, the time axis represents the elapsed time since the magnetic head passed the reference position. This figure shows the timing of servo data writing for a certain servo region SV at three radial positions.

[0052] In the comparative example, the ODS method is used. Therefore, as shown in Figure 21, the length of the servo region SV in the time axis becomes shorter as you get closer to the outer edge.

[0053] Furthermore, in the comparative example, for one servo region SV, servo data is written when the count value of the servo clock (or its frequency divider clock) reaches a common value regardless of the radial position. As the servo clock frequency increases closer to the outer edge, the timing of servo data recording becomes earlier as you get closer to the outer edge, as shown in Figure 21.

[0054] The reading of servo data is controlled by a servo gate signal. The servo gate signal indicates whether or not reading servo data is permitted. When the servo gate signal is open, reading servo data is permitted. When the servo gate signal is closed, reading servo data is not permitted.

[0055] When the magnetic head has passed through a certain servo region SV and is moving toward the next region, the SoC determines the timing to open the servo gate signal for reading the servo data of the next servo region SV, based on the time when the sync mark SN was detected in the servo region SV that the magnetic head had passed through.

[0056] In the comparative example shown in Figure 21, the position on the time axis where the servo data is written differs for each radial position. Therefore, when the SoC moves the magnetic head radially, it is necessary to determine the timing to open the servo gate signal by considering both the radial position when the magnetic head passes through a certain servo region SV and the radial position when the magnetic head reaches the next servo region SV. In other words, the calculation required to determine the timing to open the servo gate signal is complicated.

[0057] In the first embodiment, the write position of the servo data is designed to facilitate the determination of the timing for opening the servo gate signal.

[0058] Figure 6 is a diagram illustrating the servo data writing method according to the first embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis. The time axis represents the elapsed time since the magnetic head 22 passed the reference position. In other words, the time axis can be considered as the circumferential movement time of the magnetic head 22 with respect to the timing when the magnetic head 22 passed the reference position. The movement time is the time it took for the magnetic head 22 to move relative to the magnetic disk 11. Hereafter, the circumferential movement time of the magnetic head 22 with respect to the timing when the magnetic head 22 passed the reference position may be abbreviated as the temporal position.

[0059] This figure shows the timing of servo data light for servo regions SV#i and SV#(i+1) at three radial positions. The three radial positions, from closest to the outer edge, are the radial position of track #N, the radial position of track #(N+a), and the radial position of track #(N+b).

[0060] In the first embodiment, within the same servo region SV, the temporal position at which the preamble PR is lit is aligned across all radial positions. In other words, the preamble PR is lit at the circumferential position where the circumferential movement time of the magnetic head 22, relative to the timing when the magnetic head 22 passes a reference position on the circumference, is aligned across all radial positions. Therefore, as shown in Figure 6, the temporal position at which the preamble PR is lit is aligned across the radial positions of track #N, track #(N+a), and track #(N+b).

[0061] As described above, writing the servo data makes the calculation required to determine the timing for opening the servo gate signal easier compared to the comparative example.

[0062] As an example, consider the case where the magnetic head 22 moves along track #N and passes through servo region SV#i. In such a case, if the SoC 30 opens the servo gate signal SG after time t1 has elapsed since detecting the sync mark SN in servo region SV#i, it is possible to read the servo data written to servo region SV#(i+1) from the beginning, regardless of the track 41 to which the magnetic head 22 is moving.

[0063] As another example, consider the case where the magnetic head 22 moves along track #(N+a) and passes through servo region SV#i. In such a case, if the SoC 30 opens the servo gate signal SG after time t2 has elapsed since detecting the sync mark SN in servo region SV#i, it will be possible to read the servo data written to servo region SV#(i+1) from the beginning, regardless of the track 41 to which the magnetic head 22 moves.

[0064] Thus, the SoC30 can determine the timing for opening the servo gate signal based on the radial position where the sync mark SN is detected, regardless of the radial position of the destination. In other words, the calculation required to determine the timing for opening the servo gate signal SG becomes easier compared to the comparative example.

[0065] (Second embodiment) When the rotational speed of the magnetic disk 11 fluctuates, the detection time interval of the sync mark SN fluctuates. The SoC 30 may have a function to correct the servo clock frequency based on the amount of deviation in the detection time of the sync mark SN when the detection time of the sync mark SN deviates from the ideal detection time. This function is referred to as the rotational fluctuation tracking function. The ideal detection time is the detection time of the sync mark SN when the magnetic disk 11 is rotating at a set rotational speed. The rotational fluctuation tracking function allows the servo clock frequency to follow the rotational fluctuations of the magnetic disk 11.

[0066] According to the comparative example, the detection time of the sync mark SN varies depending on the radial position. Therefore, even if the rotational speed of the magnetic disk does not fluctuate, the interval of the detection time of the sync mark SN fluctuates according to the radial movement of the magnetic head while the magnetic head is moving radially. Consequently, if the above-mentioned rotational fluctuation tracking function is implemented, even if the rotational speed of the magnetic disk does not fluctuate, unintended servo clock correction may occur, which is expected to interfere with servo control. For example, it may become difficult to open the servo gate signal at the correct timing.

[0067] In the second embodiment, the write position of the servo data is designed so that the interval between detection times of the sync mark SN does not change regardless of the radial position, provided that there is no fluctuation in the rotational speed of the magnetic disk 11.

[0068] Figure 7 illustrates an example of a servo data writing method according to the second embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis.

[0069] As shown in Figure 7, within the same servo region SV, the temporal position at which the sync mark SN is written is aligned across all radial positions. With this configuration, the detection time interval for the sync mark SN is, by design, constant at time t3 regardless of the radial position. Therefore, even if the magnetic head 22 is moving radially, the sync mark SN will be detected at time t3 intervals as long as the rotational speed of the magnetic disk 11 does not fluctuate. On the other hand, if the rotational speed of the magnetic disk 11 fluctuates, the detection time interval for the sync mark SN will deviate from time t3.

[0070] In this way, even when a rotational fluctuation tracking function is implemented, it becomes possible to prevent unintended servo clock corrections from being performed.

[0071] (Third embodiment) In the comparative example, the temporal position corresponding to the circumferential position where the burst patterns (burst patterns BP1, BP2) are written differs depending on the radial position. Therefore, the normal timing for demodulating the burst patterns is shifted between two adjacent tracks. Consequently, when the magnetic head is positioned across the boundary between two tracks, a phase error occurs in the demodulated burst pattern due to the shift in the normal timing for demodulating the burst patterns. When a phase burst is applied as the burst pattern, this phase error leads to a deterioration in the accuracy of positioning control.

[0072] In the third embodiment, the light position of the burst pattern is designed to suppress errors in the control of the burst gate and phase errors in the demodulation results of the burst pattern.

[0073] Figure 8 illustrates an example of a burst pattern lighting method according to the third embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis.

[0074] As shown in Figure 8, the temporal positions at which burst patterns BP1 and BP2 are lit are aligned across all radial positions. Therefore, deviations in the normal timing for demodulating the burst patterns are significantly suppressed. As a result, it becomes possible to significantly reduce the deterioration of positioning control accuracy.

[0075] Depending on the specifications of the SoC30, it may be difficult to adjust the light timing of the burst pattern in fine steps. In such cases, as shown in Figure 9, for example, the temporal position at which only the first burst pattern of burst pattern BP1 and burst pattern BP2, i.e., burst pattern BP1, is lit may be aligned across all radial positions. This suppresses deviations from the normal timing for demodulating the burst pattern. As a result, it becomes possible to suppress deterioration in the accuracy of positioning control.

[0076] Furthermore, if the temporal position of the light-up for only the leading burst pattern is aligned across the radial positions, the further the burst pattern is from the leading burst pattern in the circumferential direction, the greater the deviation in the normal timing for demodulating the burst pattern, which may result in insufficient suppression of the deterioration of positioning control accuracy. Therefore, as shown in Figure 10, the temporal position of the light-up for only the burst patterns other than the leading burst pattern among burst pattern BP1 and burst pattern BP2, i.e., burst pattern BP2, may be aligned across all radial positions.

[0077] (Fourth embodiment) In the first embodiment, a preamble PR; in the second embodiment, a sync mark SN; and in the third embodiment, a burst pattern were lit at each radial position at a circumferential position where their temporal positions aligned across all radial positions. Any two of the preamble PR, sync mark SN, and burst pattern may be lit at a circumferential position where their temporal positions aligned across all radial positions.

[0078] Figure 11 is a diagram illustrating an example of a servo data writing method according to the fourth embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis.

[0079] In the example shown in Figure 11, within the same servo region SV, the temporal position at which the preamble PR is lit is aligned across all radial positions, and the temporal position at which the sync mark SN is lit is aligned across all radial positions.

[0080] With this configuration, if the SoC30 opens the servo gate signal SG when time t5 has elapsed since detecting the sync mark SN, it can read the servo data written to the next servo region SV from the beginning, regardless of the radial position of the magnetic head 22 or the radial position where the sync mark SN was detected. Therefore, the calculation required to determine the timing for opening the servo gate signal SG becomes even easier.

[0081] Furthermore, similar to the second embodiment, the detection time interval for the sync mark SN is, by design, constant regardless of the radial position (in this case, constant at time t4). Therefore, even when the rotational fluctuation tracking function is implemented, it is possible to prevent unintended servo clock correction.

[0082] Furthermore, since the temporal position at which the preamble PR is lit is aligned across all radial positions, and the temporal position at which the sync mark SN is lit is also aligned across all radial positions, the number of waveforms in one period included in the preamble PR may differ depending on the radial position. Specifically, the number of waveforms in one period included in the preamble PR increases as you get closer to the outer edge.

[0083] (Fifth embodiment) Figure 12 shows another example of the shape of the servo region SV according to the fifth embodiment. In the example shown in this figure, the recording surface of the magnetic disk 11 is divided into two regions 50a and 50b that are aligned radially. In each of the two regions 50a and 50b, each servo region SV extends straight from the inner circumference to the outer circumference. However, at the boundary between region 50a and region 50b, each servo region SV is discontinuous.

[0084] For example, this phenomenon can occur when servo data is written by an SSW. In the SSW, the SoC30 writes servo data from the inner circumference to a certain radial position, and then writes servo data from the outer circumference to that radial position. As a result, the recording surface of the magnetic disk 11 is divided into two regions 50a and 50b at that radial position.

[0085] Furthermore, the direction of writing servo data to regions 50a and 50b is not limited to this. Also, the recording surface of the magnetic disk 11 may be divided into three or more regions 50 arranged radially, and each servo region SV may be discontinuous at the boundary of each region. In addition, the reference position may be discontinuous corresponding to the discontinuity of each servo region SV.

[0086] If the recording surface of the magnetic disk 11 is divided into multiple regions 50 arranged in the radial direction, any of the first, second, third, and fourth embodiments can be applied to each region 50.

[0087] Figure 13 is a diagram illustrating an example of a servo data writing method according to the fifth embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis.

[0088] Figure 13 shows the servo data light timing in regions 50a, 50b, and 50c as an example of multiple regions 50. Examples of consecutive radial positions constituting region 50a, from the outer edge, are the radial positions of track #(P-1), track #P, and track #(P+1). Examples of consecutive radial positions constituting region 50b, from the outer edge, are the radial positions of track #(Q-1), track #Q, and track #(Q+1). Examples of consecutive radial positions constituting region 50c, from the outer edge, are the radial positions of track #(R-1), track #R, and track #(R+1).

[0089] In the example shown in Figure 13, servo data is written in the same manner as in the first embodiment in each of regions 50a, 50b, and 50c. That is, the temporal position at which the preamble PR is written is aligned between all radial positions in region 50a. The temporal position at which the preamble PR is written is aligned between all radial positions in region 50b. The temporal position at which the preamble PR is written is aligned between all radial positions in region 50c. With this configuration, the same effect as in the first embodiment is obtained in each of regions 50a, 50b, and 50c.

[0090] Figure 14 illustrates another example of a servo data writing method according to the fifth embodiment. Note that the example shown in Figure 14 differs from that in Figure 13.

[0091] In the example shown in Figure 14, servo data is written in the same manner as in the second embodiment in each of regions 50a, 50b, and 50c. That is, the temporal position at which the sync mark SN is written is aligned between all radial positions in region 50a. The temporal position at which the sync mark SN is written is aligned between all radial positions in region 50b. The temporal position at which the sync mark SN is written is aligned between all radial positions in region 50c. With this configuration, the same effect as in the second embodiment is obtained in each of regions 50a, 50b, and 50c.

[0092] Figure 15 illustrates yet another example of a servo data writing method according to the fifth embodiment. Note that the example shown in Figure 15 differs from that in Figure 13.

[0093] In the example shown in Figure 15, servo data is written in the same manner as in the fourth embodiment in each of regions 50a, 50b, and 50c. That is, the temporal positions at which the preamble PR is lit are aligned across all radial positions in region 50a. Also, the temporal positions at which the sync mark SN is lit are aligned across all radial positions in region 50a. The temporal positions at which the preamble PR is lit are aligned across all radial positions in region 50b. Also, the temporal positions at which the sync mark SN is lit are aligned across all radial positions in region 50b. The temporal positions at which the preamble PR is lit are aligned across all radial positions in region 50c. Also, the temporal positions at which the sync mark SN is lit are aligned across all radial positions in region 50c. With this configuration, the same effects as in the fourth embodiment are obtained in each of regions 50a, 50b, and 50c.

[0094] Figure 16 illustrates yet another example of the servo data writing method according to the fifth embodiment. Note that the example shown in Figure 16 differs from that in Figure 13.

[0095] In the example shown in Figure 16, servo data is written in regions 50a, 50b, and 50c in the same manner as in the fourth embodiment. However, the temporal position at which the sync mark SN is written is aligned across all radial positions within regions 50a, 50b, and 50c.

[0096] With this configuration, the detection time interval for the sync mark SN is, by design, constant regardless of the radial position within regions 50a, 50b, and 50c. Therefore, even if the magnetic head 22 is moving radially within regions 50a, 50b, and 50c, it is possible to detect the sync mark SN at the same interval as long as the rotational speed of the magnetic disk 11 does not fluctuate.

[0097] (Sixth embodiment) In servo control, if detection of the sync mark SN fails, the SoC30 performs a sync search operation to search for the sync mark SN. When the sync search operation starts, the SoC30 sets the frequency to be detected in the RWC25 in order to synchronize with the pattern of the preamble PR.

[0098] In the comparative example, because the recording frequency differs depending on the radial position, the calculation of the frequency to set for RWC becomes complex when the sync search operation is initiated while the magnetic head is moving at high speed in the radial direction. For example, the SoC predicts the radial position where the next servo data will be read based on the radial movement speed and travel time of the magnetic head. The SoC then sets the recording frequency for the predicted radial position to RWC.

[0099] However, accurately predicting the radius position where the next servo data will be read is difficult. Therefore, it may not be possible to set the appropriate frequency for RWC. If the appropriate frequency cannot be set for RWC, a runaway seek control may occur.

[0100] According to the sixth embodiment, the radial direction of the magnetic disk 11 is divided into multiple regions, and these multiple regions include a region in which the recording frequency of the servo data is constant regardless of the radial direction.

[0101] Figure 17 is a diagram illustrating an example of a servo data writing method according to the sixth embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis.

[0102] Figure 17 shows the write timing of the servo data in regions 60a, 70a, 60b, 70b, and 60c. Regions 60a, 70a, 60b, 70b, and 60c are arranged in this order from the inner circumference.

[0103] In regions 60a, 60b, and 60c, the CDS method is used, meaning the recording frequency of the servo data is gradually changed in the radial direction so that the recording frequency is higher on the outer circumference than on the inner circumference. The first, second, third, fourth, or fifth embodiment may or may not be applied to regions 60a, 60b, and 60c.

[0104] In regions 70a and 70b, the recording frequency of servo data is constant regardless of the radial position. In other words, in regions 70a and 70b, the recording frequency of servo data is common at a certain value across multiple consecutive radial positions. However, in the example shown in Figure 17, the recording frequency of servo data in region 70b is higher than the recording frequency of servo data in region 70a. Regions 70a and 70b are referred to as constant frequency regions.

[0105] Figure 18 is a flowchart showing an example of a sync search operation according to the sixth embodiment.

[0106] If the SoC30 fails to detect the sync mark SN when the magnetic head 22 passes through a certain servo region SV (S101), it starts a sync search operation. In the sync search operation, the SoC30 starts counting the time since the position of the magnetic head 22 was acquired based on the servo data (S102). The time counted in S102 is referred to as the travel time, meaning the time the magnetic head 22 has traveled since the position of the magnetic head 22 was acquired based on the servo data.

[0107] The SoC30 identifies a constant frequency region that the magnetic head 22 will reach in the near future based on the radial movement speed and movement time of the magnetic head 22 (S103).

[0108] For example, if the magnetic head 22 fails to detect the sink mark SN while moving in the OD direction through region 60b, and it is estimated that the magnetic head 22 will then reach region 70b based on the radial movement speed and movement time of the magnetic head 22, the SoC 30 identifies region 70b as a constant frequency region to be reached in the near future.

[0109] Furthermore, for example, if the magnetic head 22 fails to detect the sync mark SN while moving in the ID direction through region 60b, and it is estimated based on the radial movement speed and movement time of the magnetic head 22 that the magnetic head 22 will next reach region 70a, the SoC 30 identifies region 70a as a constant frequency region to be reached in the near future.

[0110] The SoC30 sets the recording frequency of the servo data in the specified constant frequency region to the RWC25 (S104). This allows the SoC30 to synchronize with the pattern of the preamble PR of the servo region SV when the magnetic head 22 passes through the servo region SV in the specified constant frequency region, enabling the detection of the sync mark SN.

[0111] If sync mark detection is successful (S105: No), the sync search operation ends. If sync mark detection is successful (S105: Yes), control transitions to S103, and SoC30 identifies another constant frequency region.

[0112] Thus, regions 70 are provided on both the inner and outer sides of the region 60 where servo data is recorded using the CDS method, where the recording frequency of the servo data is constant regardless of the radial position. Therefore, in the sync search operation, it becomes possible to easily and appropriately set the frequency to be detected.

[0113] Furthermore, in order to ensure that the magnetic head 22 reliably passes through the constant frequency region identified by the processing in S103, the radial length L of each region 70 may be set to satisfy the following equation (1), for example, as shown in Figure 19. SV V is the time interval during which the magnetic head 22 passes through the servo region SV. seekmax This is the maximum seek speed, that is, the maximum radial movement speed of the magnetic head 22. L≧T SV *V seekmax ...(1)

[0114] Note that there may be regions 70 to which the above equation (1) does not apply.

[0115] Figure 20 illustrates another example of a servo data writing method according to the sixth embodiment. In this figure, the vertical axis represents the radial position, and the horizontal axis represents the time axis.

[0116] In the example shown in Figure 20, the recording frequency of the servo data in region 70a is equal to the recording frequency of the servo data in region 70b. In this way, a common frequency may be applied as the recording frequency of the servo data in two or more regions 70. This makes it possible to omit the processing S103 shown in Figure 18.

[0117] (Summary) According to the first to fifth embodiments, the recording frequency of servo data differs at multiple consecutive radial positions (referred to as multiple first radial positions) in the magnetic disk 11. In the examples described above, the multiple first radial positions are the radial positions of multiple tracks 41 that are radially consecutive. In each servo region SV, a specific type of servo data fragment (referred to as the first data fragment) from the servo data is written to the circumferential position (referred to as the first circumferential position) at each first radial position where the temporal position, that is, the circumferential movement time of the magnetic head 22 with respect to the timing when the magnetic head 22 passes a reference position on the circumference, aligns among the multiple first radial positions.

[0118] The first data segment is either the preamble PR, the sync mark SN, or the burst pattern (burst pattern BP1 or burst pattern BP2).

[0119] Since the temporal position at which the first data fragment is written is aligned at multiple first radial positions, suitable servo control becomes possible. Specifically, for example, if the first data fragment is a preamble PR, the calculation required to determine the timing of opening the servo gate signal becomes easier, as described in the first embodiment. For example, if the first data fragment is a sync mark SN, as described in the second embodiment, it becomes possible to prevent unintended servo clock correction even when a rolling fluctuation tracking function is implemented. For example, if the first data fragment is a burst pattern, as described in the third embodiment, it is possible to improve the accuracy of positioning control compared to the comparative example.

[0120] Furthermore, according to the fourth embodiment, a servo data piece (referred to as the second data piece) of a different type from the first data piece is written to the magnetic disk 11 at a circumferential position (referred to as the second circumferential position) that is different from the first circumferential position and whose temporal position is aligned among a plurality of first radial positions.

[0121] In the example shown in Figure 11, the first data piece is the preamble PR, and the second data piece is the sync mark SN. The number of waveforms in one period contained in the first data piece, the preamble PR, differs for each first radius position.

[0122] Therefore, the calculations required to determine the timing for opening the servo gate signal SG become easier. Even if a rotational fluctuation tracking function is implemented, it becomes possible to prevent unintended servo clock corrections.

[0123] As described in the fourth embodiment, the first and second data pieces are not limited to the examples described above.

[0124] Furthermore, according to the fifth embodiment, the recording frequency of servo data on the magnetic disk 11 differs for each of the following consecutive second radial positions, which are distinct from the following consecutive first radial positions. In the specific configuration described in the fifth embodiment, for example, the following consecutive first radial positions are one of the regions 50a, 50b, and 50c, and the following consecutive second radial positions are another one of the regions 50a, 50b, and 50c. In each of the multiple servo regions SV, a first data fragment is written to the circumferential position (referred to as the third circumferential position) at each second radial position where the temporal position aligns among the multiple second radial positions.

[0125] In the examples shown in Figures 13 and 14, the first data segment is either a preamble PR or a sink mark SN. The first data segment may also be a burst pattern.

[0126] Furthermore, according to the fifth embodiment, in each of the multiple servo regions SV, a servo data piece (referred to as the third data piece) different from the first data piece is written to the magnetic disk 11 at the circumferential position (referred to as the fourth circumferential position) at each first radial position where the temporal position aligns among the multiple first radial positions. The third data piece is written to the circumferential position (referred to as the fifth circumferential position) at each second radial position where the temporal position aligns among the multiple second radial positions.

[0127] In the examples shown in Figures 15 and 16, the first data piece is the preamble PR, and the third data piece is the sync mark SN. Note that the first and second data pieces are not limited to these.

[0128] Furthermore, as shown in the example in Figure 16, the temporal position corresponding to the fourth circumferential position, that is, the temporal position at which the sync mark SN is lit at multiple first radial positions, is equal to the temporal position corresponding to the fifth circumferential position, that is, the temporal position at which the sync mark SN is lit at multiple second radial positions.

[0129] Therefore, even while the magnetic head 22 is moving through a radial range that includes multiple first radial positions and multiple second radial positions, it becomes possible to detect the sync mark SN at the same intervals, as long as the rotational speed of the magnetic disk 11 does not fluctuate.

[0130] Furthermore, according to the sixth embodiment, in the magnetic disk 11, the recording frequency of servo data differs for each of the following consecutive radial positions (referred to as multiple first radial positions). For the following consecutive radial positions located on the inner circumference side of the multiple first radial positions (referred to as multiple second radial positions), the recording frequency of servo data is common to a certain value (referred to as the first value). For the following consecutive radial positions located on the outer circumference side of the multiple first radial positions (referred to as multiple third radial positions), the recording frequency of servo data is common to a certain value (referred to as the second value).

[0131] In the example shown in Figure 17, region 60b corresponds to multiple first radial positions. When region 60b corresponds to multiple first radial positions, region 70a corresponds to multiple second radial positions, and region 70b corresponds to multiple third radial positions.

[0132] Therefore, the process of obtaining the frequency to be set for the RWC25 during sync search operation becomes easier. In other words, optimal servo control becomes possible.

[0133] Furthermore, according to the sixth embodiment, the length of the radial range consisting of a plurality of second radial positions and the length of the radial range consisting of a plurality of third radial positions are greater than or equal to the length obtained by multiplying the time interval during which the magnetic head 22 passes through the servo region SV by the maximum seek speed.

[0134] Therefore, even when the magnetic head 22 is moving radially at high speed (e.g., maximum seek speed), it is possible to reliably pass the magnetic head 22 through multiple second radial positions or multiple third radial positions during the sync search operation.

[0135] Furthermore, it is possible that only one of the lengths of the radial range consisting of multiple second radial positions and the lengths of the radial range consisting of multiple third radial positions is greater than or equal to the length obtained by multiplying the time interval during which the magnetic head 22 passes through the servo region SV by the maximum seek speed.

[0136] Furthermore, according to the sixth embodiment, the first value, i.e., the recording frequency of servo data at multiple second radial positions, is equal to the second value, i.e., the recording frequency of servo data at multiple third radial positions.

[0137] Therefore, the process of obtaining the frequency to be set for the RWC25 during sync search operation becomes even easier.

[0138] In the above explanation, each of the multiple first radial positions is assumed to be a position on track 41. Each of the multiple first radial positions may be a representative position of two or more consecutive tracks 41. The same applies to each of the multiple second radial positions and each of the multiple third radial positions.

[0139] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0140] 1 Magnetic disk drive, 2 Host, 11 Magnetic disk, 12 SPM, 13 Ramp, 15 Actuator arm, 16 VCM, 21 SVC, 22 Magnetic head, 22r Read head, 22w Write head, 23 HDC, 24 Preamplifier, 25 RWC, 26 Processor, 28 FROM, 29 DRAM, 41 Track, 50, 50a, 50b, 50c, 60, 60a, 60b, 60c, 70, 70a, 70b areas, SV Servo area.

Claims

1. Magnetic head and A magnetic disk comprising: multiple servo regions arranged at equal intervals in the circumferential direction, each containing multiple data fragments; the recording frequency of the servo data differs for each of the multiple first radial positions; and in each of the multiple servo regions, the first data fragment among the multiple data fragments is written to a first circumferential position where the circumferential movement time of the magnetic head, based on the timing when the magnetic head passes a reference position on the circumference, is aligned among the multiple first radial positions; A magnetic disk drive equipped with the following features.

2. The first data segment is a preamble, sync mark, or burst pattern. The magnetic disk device according to claim 1.

3. In the magnetic disk, in each of the plurality of servo regions, a second data piece, which is different from the first data piece among the plurality of data pieces, is written to a second circumferential position that is different from the first circumferential position where the movement time is equal among the plurality of first radial positions. The magnetic disk device according to claim 1.

4. The first data piece is a preamble, and the second data piece is a sync mark. The number of waveforms in one period included in the preamble that are lit at the first circumferential position is different among the plurality of first radial positions. The magnetic disk device according to claim 3.

5. The magnetic disk has a recording frequency that differs for each of the multiple second radial positions, which are separate from the multiple consecutive first radial positions, and in each of the multiple servo regions, the first data piece is written to a third circumferential position where the movement times are the same among the multiple second radial positions. The magnetic disk device according to claim 1.

6. The first data fragment is a preamble or sync mark. The magnetic disk device according to claim 5.

7. In each of the plurality of servo regions, the magnetic disk has A third data piece, which is different from the first data piece among the plurality of data pieces, is written to a fourth circumferential position that is different from the first circumferential position where the aforementioned travel time is the same among the plurality of first radial positions. The third data fragment is written to a fifth circumferential position that is different from the third circumferential position where the aforementioned travel time is the same among the plurality of second radial positions. The magnetic disk device according to claim 5.

8. The first data piece is a preamble, and the third data piece is a sync mark. The magnetic disk device according to claim 7.

9. The travel time corresponding to the fourth circumferential position is equal to the travel time corresponding to the fifth circumferential position. The magnetic disk device according to claim 8.

10. Magnetic head and A magnetic disk having multiple servo regions, each containing multiple data fragments, arranged circumferentially and written to them at equal intervals in the circumferential direction, wherein the recording frequency of the servo data differs for each of the multiple consecutive first radial positions, the recording frequency is common at a first value among the multiple consecutive second radial positions on the inner circumference of the multiple first radial positions, and the recording frequency is common at a second value among the multiple consecutive third radial positions on the outer circumference of the multiple first radial positions. A magnetic disk drive equipped with the following features.

11. The length of the radial range consisting of the plurality of second radial positions or the length of the radial range consisting of the plurality of third radial positions is greater than or equal to the length obtained by multiplying the time interval during which the magnetic head passes through the plurality of servo regions by the maximum seek speed. The magnetic disk device according to claim 10.

12. The first value and the second value are equal. The magnetic disk device according to claim 10.

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