disc device

Abstract

The present disclosure provides a disc device capable of improving the accuracy of positioning control of a head. According to one embodiment, in the disc device, when a controller positions a head at a target data track based on servo information read from a servo track, the controller adjusts a correction value of a radial position of the servo track based on a ratio between an amplitude of a correction value spectrum of the radial position of the servo track at a first circumferential position and an amplitude of a correction value spectrum of the radial position of the servo track at a second circumferential position. At the first circumferential position, a relative speed of a change in the radial position of the servo track with respect to a radial position of the target data track is a first speed. At the second circumferential position, a relative speed of a change in the radial position of the servo track with respect to the radial position of the target data track is a second speed.

Description

[0001] This application claims priority to Japanese Patent Application No. 2022-149286 (filed on September 20, 2022). This application includes all contents of the basic application by reference to that basic application. Technical Field

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

[0003] In a disk assembly having a head and a disk, multiple servo tracks and multiple data tracks are defined on the disk. The disk assembly positions the head onto the target data track based on servo information read from the servo tracks. At this point, in the disk assembly, it is desirable to appropriately correct the radial position of the servo tracks to improve the accuracy of the head's positioning control. Summary of the Invention

[0004] Embodiments of the present invention provide a disc device capable of improving the accuracy of head positioning control.

[0005] According to an embodiment, a disk apparatus having a head, a disk, and a controller is provided. On the disk, a plurality of servo tracks are defined concentrically with respect to a first center. On the disk, a plurality of data tracks are defined concentrically with respect to a second center. The second center is different from the first center. When the controller positions the head to a target data track based on servo information read from the servo tracks, it adjusts the correction value of the radial position of the servo tracks according to the ratio of the amplitude of the correction value spectrum of the radial position of the servo tracks at a first circumferential position to the amplitude of the correction value spectrum of the radial position of the servo tracks at a second circumferential position. At the first circumferential position, the relative speed of change of the radial position of the servo tracks relative to the radial position of the target data tracks is a first speed. At the second circumferential position, the relative speed of change of the radial position of the servo tracks relative to the radial position of the target data tracks is a second speed. Attached Figure Description

[0006] Figure 1 This is a diagram showing the configuration of the disk device in the embodiment.

[0007] Figure 2 This is a top view showing the configuration of the disk in the implementation method.

[0008] Figure 3 This is a diagram illustrating the configuration of the servo sector in the implementation method.

[0009] Figure 4 This is a diagram showing the center of the servo track and the center of the data track in the implementation method.

[0010] Figure 5This is a graph showing the change in the radial position of the data track relative to the radial position of the servo track in the implementation method.

[0011] Figure 6 This is a flowchart illustrating the actions of the controller in the implementation method.

[0012] Figure 7 This is a graph showing the distribution of RRO correction values ​​relative to the circumferential position in the implementation method.

[0013] Figure 8 This is a graph showing the distribution of the radial spectrum of the RRO correction value relative to the circumferential position in the implementation method.

[0014] Figure 9 This is a graph showing the calculated amplitude ratio of the radial spectrum of the RRO correction value relative to multiple circumferential positions in the implementation method.

[0015] Figure 10 It is a graph showing the distribution of the DC spacing variation relative to the circumferential position in the implementation method.

[0016] Figure 11 (a)~ Figure 11 (c) is a graph representing the weighted average of the estimated values ​​for DC spacing variations in this embodiment. Figure 11 (d) Figure 11 (f) is a graph representing the inverse weighted radial spectrum for the RRO correction value.

[0017] Figure 12 (a) is a graph representing the radial spectrum of the inversely weighted RRO correction value in the implementation method. Figure 12 (b) is a graph showing the distribution of the inversely weighted RRO correction values ​​relative to the radial and circumferential positions.

[0018] Figure 13 (a) is a graph showing the distribution of the inversely weighted RRO correction values ​​in the implementation method. Figure 13 (b) is a graph showing the distribution of the weighted DC spacing variation estimates. Figure 13 (c) is a graph showing the distribution of the adjusted RRO correction values.

[0019] Figure 14 (a)~ Figure 14 (c) is a diagram illustrating the characteristics of offset writing in the implementation.

[0020] Label Explanation

[0021] 1-pan device; 11-pan; 22 heads; 30 controllers. Detailed Implementation

[0022] Hereinafter, the disk device according to the embodiments will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to this embodiment.

[0023] (Implementation Method)

[0024] The disk device of the embodiment has a head and a disk, on which multiple servo tracks and multiple data tracks are defined, and improvements are implemented to improve the accuracy of positioning and controlling the head on the target data track.

[0025] For example, disk device 1 Figure 1 It is constructed as shown. Figure 1 This is a diagram showing the configuration of disk device 1.

[0026] Disk device 1 is connected to host 2 via a communication medium. The communication medium can be a wired communication line such as an I / F bus cable. Disk device 1 can receive access commands such as write commands and read commands from host 2, and can send corresponding responses to host 2.

[0027] The disk device 1 has a disk 11 on which a magnetic layer is formed. The disk 11 is a generally circular recording medium, which can be a magnetic disk or an optical disk. The disk device 1 writes information to the disk 11 and reads information from the disk 11 according to access commands.

[0028] Data writing and reading are performed via head 22. Specifically, in addition to disk 11, disk device 1 also includes spindle motor 12, ramp 13, actuator arm 15, voice coil motor (VCM) 16, motor driver IC (Integrated Circuit) 21, head 22, hard disk controller (HDC) 23, head IC 24, read / write channel (RWC) 25, processor 26, RAM 27, FROM (Flash Read Only Memory) 28, and buffer memory 29.

[0029] The disk 11 rotates at a predetermined speed by a coaxially mounted spindle motor 12. The spindle motor 12 is driven by a motor driver IC 21.

[0030] The processor 26 controls the rotation of the spindle motor 12 and the VCM 16 via the motor driver IC 21.

[0031] The head 22 moves relative to the surface of the disk 11. Furthermore, the head 22 writes and reads information relative to the surface of the disk 11 through its write head 22w and read head 22r.

[0032] The head 22 is mounted on the front end of the actuator arm 15. The head 22 moves radially relative to the surface of the disk 11 by the VCM16 driven by the motor driver IC21. In addition, as the disk 11 rotates, the head 22 moves relative to the surface of the disk 11 in the circumferential direction.

[0033] When the rotation of disk 11 stops, head 22 moves onto ramp 13. Ramp 13 is configured to hold head 22 in the position away from disk 11.

[0034] During reading, the head IC24 amplifies and outputs the signal read from disk 11 by head 22, supplying it to RWC25. Conversely, during writing, the head IC24 amplifies the signal corresponding to the data to be written, supplied from RWC25, and supplies it to head 22.

[0035] HDC23 controls the transmission and reception of data between the HDC23 and the host 2 via the I / F bus, controls the buffer memory 29, and performs error correction processing on the read data.

[0036] The buffer memory 29 is used as a buffer for data to be sent and received between the host 2 and the disk 11. For example, the buffer memory 29 is used to temporarily store data to be written to the disk 11 or data that has been read from the disk 11.

[0037] The buffer memory 29 may be composed of, for example, a volatile memory capable of high-speed operation. The type of memory constituting the buffer memory 29 is not limited to a specific type. For example, the buffer memory 29 may be composed of DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), or a combination thereof.

[0038] RWC25 modulates the data to be written from HDC23 and supplies it to head IC24. Additionally, RWC25 demodulates the signal read from disk 11 and supplied by head IC24, outputting it as digital data to HDC23.

[0039] Processor 26 is, for example, a CPU (Central Processing Unit). RAM 27, FROM (Flash Read Only Memory) 28 and buffer memory 29 are connected to processor 26.

[0040] FROM28 is a non-volatile memory. Firmware (program data) and various operational parameters are stored in FROM28. Additionally, firmware can also be stored on disk 11.

[0041] RAM 27 is composed of, for example, DRAM, SRAM, or a combination thereof. RAM 27 is used as an operational memory by the processor 26. RAM 27 is used as an area for loading firmware and an area for storing various management data.

[0042] The processor 26 performs overall control of the disk device 1 according to the firmware stored in the FROM 28 or disk 11. For example, the processor 26 loads the firmware from the FROM 28 or disk 11 into the RAM 27, and executes the control of the motor driver IC 21, head IC 24, RWC 25, HDC 23, etc. according to the loaded firmware.

[0043] Furthermore, the configuration including RWC25, processor 26, and HDC23 can also be considered as controller 30. In addition to these, controller 30 may also include other elements (such as RAM27, FROM28, buffer memory 29, or RWC25, etc.).

[0044] Alternatively, the firmware program can also be stored on disk 11. Furthermore, some or all of the functions of processor 26 can be implemented using hardware circuits such as FPGA (Field-Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0045] Figure 2 This is a schematic diagram showing an example of the configuration of the disk 11 in the first embodiment. Furthermore, in the disk 11, regarding the radial direction, the direction from the outer periphery to the inner periphery of the disk 11 is described as the inward direction. The direction from the inner periphery to the outer periphery of the disk 11 is described as the outward direction. Additionally, in... Figure 2 An example of the rotation direction of disk 11 is shown in the figure.

[0046] On disk 11, servo information is written during the manufacturing process. Figure 2 As an example of a servo region configuration in which servo information is written, a radially configured servo region 42 is shown. The servo information will be described later.

[0047] Data areas 43 for writing data are provided between servo areas 42. One servo area 42 and one data area 43 following the servo area 42 constitute a servo sector 44. A plurality of concentric servo tracks 41 defined by servo information are provided radially on disk 11.

[0048] Figure 3This is a schematic diagram illustrating an example of the configuration of servo region 42. As shown in this diagram, servo region 42, which together with data region 43 constitutes a servo sector 44, has a servo marker section 51, a Gray code section 52, a pulse train section 53, and an RRO section 54.

[0049] The servo marker is recorded in the servo marker section 51. The servo marker indicates the beginning of the servo area 42 in the circumferential direction of disk 11.

[0050] Gray code is recorded in Gray code segment 52. Gray code is digital data representing the number of the servo track.

[0051] Servo pulse train data is recorded in pulse train segment 53. This servo pulse train data is used to detect the distance of the head 22 from the center of the track. The servo pulse train data defines the center of each servo track, in other words, each servo track. The servo pulse train data may consist, for example, of an area pattern of multiple phases with phases offset from each other.

[0052] RRO correction data is recorded in RRO section 54. The position of the servo track 41, as specified by the servo pulse train data, sometimes deviates from the ideal circular shape (e.g., an imaginary circle). In such cases, the radial position of the servo track 41 includes an error caused by radial wobble synchronized with the rotation of the disk 11. This wobble is referred to as RRO. That is, RRO is the rotational synchronization component of the radial position deviation of the servo track 41, having a first-order component and components of second-order and higher.

[0053] During the manufacturing process, servo markers, Gray codes, and servo burst data are written to disk 11, for example, via a servo writer or self-servo writing (SSW). Disk 11 is mounted in a housing. At this time, depending on the configuration state of disk 11, Figure 4 The center 82 of the servo track 41 shown is off-center from the rotation center 81 of the spindle motor 12. The rotation center 81 of the spindle motor 12 can also be referred to as the rotation center 81 of the disk 11. The multiple servo tracks 41 are multiple concentric circles centered on the center 82.

[0054] Therefore, data tracks 61 are defined as depicting an ideal circular orbit centered at rotation center 81. This ideal circular orbit is also called an imaginary circular orbit. The imaginary circular orbit corresponds to the first-order RRO. Multiple data tracks 61 are multiple concentric imaginary circles centered at center 81. By defining each data track 61 with an imaginary circular orbit, the influence of the first-order component of RRO can be reduced, but the second-order and higher-order components of RRO still remain. Therefore, as described later, RRO correction data corresponding to the second-order and higher-order components of RRO is calculated, and the calculated RRO correction data is written into RRO segment 54 (see reference). Figure 3 ).

[0055] If we take Figure 4 Using data track 61, represented by a solid line, as a reference, then... Figure 4 The radial position of the servo track 41, indicated by the dashed line, varies, for example, along a sine wave with a cycle of one week.

[0056] In this regard, if one cycle of data track 61 is shown flatly in the circumferential direction, it becomes Figure 5 As shown. Figure 5 This is a graph showing the change in the radial position of data track 61 relative to the radial position of servo track 41. Figure 5 In the diagram, the vertical axis represents the radial position, and the horizontal axis represents the circumferential position. Figure 5 The upper side of the middle indicates the inward direction (see reference). Figure 2 ), Figure 5 The lower side of the symbol indicates the outward direction. Figure 5 In the diagram, a solid line represents the center of data track 61, a dashed line represents the center of servo track 41, and a dashed line represents the decimal part of servo track 41. The decimal part of servo track 41 corresponds to the radial position of servo track 41 offset from the center of the track.

[0057] If we take Figure 5 Using data track 61, represented by a solid line, as a reference, then... Figure 5 The radial position of the servo track 41, represented by a dashed line, varies, for example, along a sine wave with a cycle of one revolution. Similarly, if... Figure 5 Using data track 61, represented by a solid line, as a reference, then... Figure 5 The radial position of the fractional part of the servo track 41, indicated by dashed lines, varies, for example, along a sine wave with a cycle of one week.

[0058] During servo writing, servo track 41 may be affected by external forces or other factors, resulting in a deviation of the track spacing from the ideal average, which may lead to writing. This deviation of the average track spacing is called DC pitch variation. The position between servo tracks is calculated based on servo pulse train data, but since the servo pulse train data is standardized between servo tracks, DC pitch variation is essentially undetectable from the servo pulse train data. However, for example... Figure 5 In this way, by tracking control in which the servo track 41 changes position radially along a sine wave with a period of 1 week, it is possible to generate a circumferential position that can be corrected for DC pitch variation as RRO.

[0059] The ease of correcting for DC spacing variations varies depending on the circumferential position. Let's assume... Figure 5Of the multiple data tracks 61-(k-4) to 61-(k+1) shown, data track 61-k is the target data track. When the head 22 is positioned and controlled on the target data track 61-k, the head 22, for example, moves along the target data track 61-k... Figure 5 The head 22 moves from left to right. The target data track 61-k follows an imaginary circular path, successively crossing servo tracks 41-n, 41-(n+1), 41-(n+2), 41-(n+1), 41-n, 41-(n-1), 41-(n-2), and 41-(n-1) with a sinusoidal wave of one revolution. Correspondingly, as the head 22 moves circumferentially along the data track 61-k, the radial velocity of the servo track 41 relative to the center of the data track 61-k varies depending on the circumferential position of the head 22.

[0060] For example, at the circumferential positions of 0 / 4 Hz, 2 / 4 Hz, and 4 / 4 Hz (i.e., the circumferential positions corresponding to the phases of the sine wave of 0°, 180°, and 360°), data track 61-k approaches, crosses, or moves away from servo track 41 with a radial velocity greater than 0. At these circumferential positions of 0 / 4 Hz, 2 / 4 Hz, and 4 / 4 Hz, in the case of DC pitch variation in the servo track, the error between the expected change in the radial position of the servo track based on the velocity of head 22 and the change in the radial position calculated based on the servo information always produces a certain amount, which can be considered as RRO. In other words, DC pitch variation is easily considered as RRO. Therefore, at the circumferential positions of 0 / 4 Hz, 2 / 4 Hz, DC pitch variation can be easily corrected using RRO correction.

[0061] However, at the circumferential positions of 1 / 4 circumference and 3 / 4 circumference (i.e., the circumferential positions corresponding to the phases of the sine wave of 90° and 270°), data track 61-k is approximately parallel to servo track 41, and data track 61-k runs parallel to servo track 41 in the circumferential direction with a radial velocity of approximately 0. At this time, in the servo sector at the circumferential positions of 1 / 4 circumference and 3 / 4 circumference, the expected change in the radial position of the servo track based on the velocity of head 22 is 0. Therefore, in the change in radial position calculated based on servo information, the DC pitch variation is difficult to consider as RRO. Consequently, at the circumferential positions of 1 / 4 circumference and 3 / 4 circumference, it is difficult to correct the DC pitch variation using RRO correction. As a result, the positioning control accuracy of head 22 decreases, and if it is during write processing, there is a possibility of overwriting and erasing adjacent data tracks 61-(k+1) and 61-(k-1).

[0062] Therefore, the controller 30 estimates the RRO correction value for the circumferential position of the DC pitch change that is not easily considered as the RRO, based on the RRO correction value for the circumferential position of the DC pitch change that is easily considered as the RRO. The estimated DC pitch change value, estimated based on the estimation result, is then combined with the original RRO correction value to adjust the RRO correction value. The controller 30 can also adjust the RRO correction value for the radial position of the servo track based on the amplitude of the radial spectrum of the RRO correction value that is not easily considered as the RRO and the amplitude of the radial spectrum of the RRO correction value that is easily considered as the RRO. Using the adjusted RRO correction value, the head 22 is positioned on the target data track 61. This improves the positioning control accuracy of the head 22 using the RRO correction value and improves the tolerance for offset writing.

[0063] Controller 30 can also be like Figure 6 The RRO correction value is adjusted to take into account the DC spacing variation, as shown. Figure 6 This is a flowchart showing the actions of controller 30.

[0064] The radial variation of the RRO correction value includes a pitch variation component in the radial position of the servo track 41 relative to the target data track 61. This pitch variation includes higher-order components in the radial direction. The controller 30 determines the order (S1) to be adjusted among the multiple-order components of the radial position variation of the servo track 41 relative to the target data track 61. This order to be adjusted is set as the estimated DC pitch variation. The controller 30 calculates the ratio of the amplitude of the radial spectrum of the correction value of the radial position of the servo track 41 at the circumferential position CP1 to the amplitude of the radial spectrum of the correction value of the radial position of the servo track 41 at the circumferential position CP2, and determines the order to be adjusted based on the calculated ratio.

[0065] Circumferential position CP1 is the circumferential position where the DC pitch variation is easily considered as RRO compared to circumferential position CP2. Circumferential position CP1 is the position where the relative velocity of the change in the radial position of the servo track 41 relative to the radial position of the target data track 61 is v1. Circumferential position CP1 can also be the position where the relative velocity of the change in the radial position of the servo track 41 relative to the radial position of the target data track 61 is the maximum velocity. Circumferential position CP1 can be a 0 / 4 circumference, 2 / 4 circumference, or 4 / 4 circumference position (i.e., the circumferential position corresponding to the phases of the sine wave of 0°, 180°, and 360°).

[0066] Circumferential position CP2 is the circumferential position where the DC pitch variation is difficult to consider as RRO compared to circumferential position CP1. Circumferential position CP2 is the position where the relative velocity of the change in the radial position of the servo track 41 relative to the radial position of the target data track 61 is velocity v2. Circumferential position CP2 can also be a position where the relative velocity of the change in the radial position of the servo track 41 relative to the radial position of the target data track 61 is approximately zero. A position with approximately zero relative velocity can also be described as a position where the target data track 61 and the servo track 41 are approximately parallel. Circumferential position CP2 can be a 1 / 4 circumference or a 3 / 4 circumference (i.e., a circumferential position corresponding to a sine wave phase of 90° or 270°).

[0067] For example, the controller 30 moves the head 22 along multiple data tracks 61 while acquiring a reproduced signal of the servo pulse train data via the head 22. The reproduced signal of the servo pulse train data is acquired each time the head 22 passes through a pulse train segment 53. In other words, the controller 30 acquires the reproduced signal of the servo pulse train data in units of servo sectors 44.

[0068] The controller 30 determines the radial position of the servo track 41 based on the reproduced signal of the servo pulse train data, and calculates the position deviation of the calculated radial position from the ideal radial position. The controller 30 calculates the RRO of the servo track 41 based on the calculated position deviation, and sets the calculated RRO of the servo track 41 as the RRO correction value. The controller 30 can also calculate the RRO correction value in units of servo sectors 44.

[0069] Therefore, controller 30 is able to obtain Figure 7 The distribution of RRO correction values ​​is shown in the figure. Figure 7 This is a graph showing the distribution of RRO correction values ​​relative to radial and circumferential positions. Figure 7 In the diagram, the vertical axis represents the radial position of disk 11, and the horizontal axis represents the circumferential position of disk 11. Figure 7 The upper side of the middle indicates the inward direction (see reference). Figure 2 ), Figure 7 The bottom side of the symbol indicates the outward direction.

[0070] The circumferential position is represented by the degree of circumferential movement relative to one revolution along the center of the data track 61. For example, the initial position is represented by 0 / 4 revolution, the position after moving 1 / 4 revolution is represented by 1 / 4 revolution, the position after moving 2 / 4 revolution is represented by 2 / 4 revolution, the position after moving 3 / 4 revolution is represented by 3 / 4 revolution, and the position after moving 4 / 4 revolution is represented by 4 / 4 revolution. Furthermore, since the servo track 41 exhibits a sinusoidal change in one cycle relative to the center of the data track 61 (see reference...), Figure 5Therefore, the degree to which the circumference shifts relative to one cycle corresponds to the phase of the sine wave. For example, the position of 0 / 4 cycle can also be expressed as 0°, the position of 1 / 4 cycle as 90°, the position of 2 / 4 cycle as 180°, the position of 3 / 4 cycle as 270°, and the position of 4 / 4 cycle as 360°.

[0071] exist Figure 7 In this context, the level of RRO correction is represented by the intensity of color. Figure 7 As shown, the darker the color, the closer it is to black, the smaller the level of the RRO correction value; the lighter the color, the closer it is to white, the larger the amplitude.

[0072] The controller 30 performs a discrete Fourier transform (DFT) in the radial direction on the RRO correction values ​​of multiple data tracks 61, including the target data track 61 and its adjacent data tracks 61. As a result, the controller 30 extracts components of multiple orders from the RRO correction values, obtaining the desired outcome. Figure 8 The distribution of the radial spectrum of the RRO correction value is shown in the figure. Figure 8 This is a graph showing the distribution of the radial spectrum of the RRO correction value relative to the circumferential position. Figure 8 In the diagram, the vertical axis represents the radial frequency of RRO, and the horizontal axis represents the circumferential position in disk 11.

[0073] The radial frequency of RRO indicates the period of variation of the corresponding component on which track, implying the order of the pitch variation. For example, when there are N data tracks in disk 11, the order n of the pitch variation can be set to a value from 0 to N-1.

[0074] exist Figure 8 In this diagram, the amplitude of the radial spectrum of the RRO correction value should be shown in color, but for ease of illustration, grayscale is used. Figure 8 The diagram shows that the closer a color is to a gray level equivalent to purple, the smaller the amplitude of the radial spectrum of the RRO correction value; conversely, the closer a color is to a gray level equivalent to red, the larger the amplitude of the radial spectrum of the RRO correction value.

[0075] use Figure 8The controller 30 calculates the average amplitude |Aavg(n)| of the radial spectrum of the RRO correction value at multiple circumferential positions CP1_1 and CP1_2, based on the distribution of the RRO correction value radial spectrum. Circumferential position CP1_1 can be a 0 / 4 circumferential position (i.e., the circumferential position corresponding to the 0° phase of the sine wave), and circumferential position CP1_2 can be a 2 / 4 circumferential position (i.e., the circumferential position corresponding to the 180° phase of the sine wave). The controller 30 can calculate the average amplitude |Aavg(n)| by summing the amplitudes of the nth-order correction value spectrum at circumferential position CP1_1 and the nth-order correction value spectrum at circumferential position CP1_2 for n = 0 to N-1, and obtaining their absolute values.

[0076] The controller 30 calculates the amplitudes |A2_1(n)| and |A2_2(n)| of the radial spectrum at each of the nth-order correction values ​​at multiple circumferential positions CP2_1 and CP2_2. The circumferential position CP2_1 can be a 1 / 4-circumferential position (i.e., a circumferential position corresponding to a 90° phase of the sine wave), and the circumferential position CP2_2 can be a 3 / 4-circumferential position (i.e., a circumferential position corresponding to a 270° phase of the sine wave). The controller 30 can obtain the absolute values ​​of the amplitudes of the radial spectrum at the nth-order correction values ​​of the circumferential position CP2_1 for n = 0 to N-1, and calculate the amplitudes |A2_1(n)|. The controller 30 can obtain the absolute values ​​of the amplitudes of the radial spectrum at the nth-order correction values ​​of the circumferential position CP2_2 for n = 0 to N-1, and calculate the amplitudes |A2_2(n)|.

[0077] The controller 30 calculates the radial spectral amplitude ratio R2_1(n) = |Aavg(n)| / |A2_1(n)| for each order n = 0 to N-1, corresponding to the circumferential position CP2_1. The controller 30 also calculates the spectral amplitude ratio R2_2(n) = |Aavg(n)| / |A2_2(n)| for each order n = 0 to N-1, corresponding to the circumferential position CP2_2. Therefore, the controller 30 obtains... Figure 9 The calculation results are as shown.

[0078] Figure 9 This is a graph showing the calculated amplitude ratios R2_1(n) and R2_2(n) of the radial spectrum relative to multiple circumferential positions for the RRO correction values. Figure 9 In the diagram, the vertical axis represents the frequency of the RRO, and the horizontal axis represents the magnitude of the spectral amplitude ratio. The frequency of the RRO corresponds to the order of the DC spacing variation. Figure 9 In the diagram, a dashed line represents the radial spectral amplitude ratio R2_1(n) corresponding to the circumferential position CP2_1, and a solid line represents the radial spectral amplitude ratio R2_2(n) corresponding to the circumferential position CP2_2.

[0079] The controller 30 considers the orders of the spacing variation n = 0 to N-1 whose spectral amplitude ratio R(n) deviates from the appropriate range as the orders with the largest deviation (error) from the appropriate value, and regards them as DC spacing variations, as the objects to be estimated. The appropriate range is as follows: Figure 9 As shown by the dashed line, the lower threshold Rth1 and the upper threshold Rth2 can be defined. The lower threshold Rth1 and the upper threshold Rth2 can be determined in advance through experiments.

[0080] exist Figure 9 In the case of radial spectral amplitude ratio R2_1(n) represented by a dashed line, controller 30 determines the order n = 28, 45, 70, 79, 87 as the order that deviates from the appropriate range. For radial spectral amplitude ratio R2_2(n) represented by a solid line, controller 30 determines the order n = 25 as the order n that deviates from the appropriate range. Controller 30 determines the order at which the DC spacing variation should be estimated to be n = 25, 28, 45, 70, 79, 87.

[0081] return Figure 6 For the order determined in S1, the controller 30 generates relational information representing the relationship between the correction value and the radial position of the servo track 41. The controller 30 uses the generated relational information to estimate the amount of change in the radial position of the servo track 41 at the circumferential position CP2 of RRO (DC pitch change) that is difficult to regard as DC pitch variation (S2).

[0082] The controller 30 can estimate the amount of change in the radial position of the servo track 41 at the circumferential position CP2 (DC pitch variation) by using the amount of change in the radial position of the servo track 41 at the circumferential position CP1, which is easily regarded as the change in DC pitch variation.

[0083] Here, the RRO correction value is defined in a form corresponding to data track 61, while the DC pitch variation is calculated corresponding to servo track 41. Therefore, the controller 30 obtains the servo target position corresponding to the RRO correction value. The controller 30 can obtain the detailed position of the pulse train signal of the pulse train segment 53 as the servo target position for the radial position of the center of the servo track 41. The controller 30 can function the DC pitch variation using the amplitude of the radial spectrum of the RRO correction value and the servo target position.

[0084] For example, the controller 30 can use the order n determined in S1 as an estimate to generate amplitude information |Vavg(n)| as shown in Equation 1. Thus, the controller 30 prepares an estimate that reflects the amplitude of the radial spectrum of the RRO correction value at the circumferential position CP1 in terms of the DC spacing variation at the circumferential position CP2.

[0085]

[0086] As shown in Equation 1, the amplitude information |Vavg(n)| represents the amplitude of the order n of the spacing variation. The amplitude information |Vavg(n)| is a function that is equal to the amplitude |Aavg(n)| at the circumferential position CP1 when n is the order of the estimated object (considered as the order of the DC spacing variation), and is 0 when n is an order other than the estimated object (not considered as the order of the DC spacing variation).

[0087] exist Figure 9 In the case of [condition], the controller 30 generates the amplitude information |Vavg(n)| as a function that is equal to the amplitude |Aavg(n)| when the order n = 25, 28, 45, 70, 79, 87, and is 0 when the order n = 0~24, 26, 27, 29~44, 46~69, 71~78, 80~86, 88~100.

[0088] If the estimated value of the DC spacing variation is set as c t (r), then the presumed value c t (r) is a function (relationship information) representing the relationship between the correction value and the radial position of the servo track 41. The controller 30 can estimate the estimated value c as shown in the following mathematical formula 2. t (r).

[0089]

[0090] In mathematical formula 2, n is the order of the spacing variation. r is the identification information of data track 61 (e.g., data track number), r = 0, 1, 2, ..., N-1. t is the identification information of servo sector 44 (e.g., servo sector number), t = 0, 1, 2, 3, ..., MaxSct-1. Data track 61 with identification information r is recorded as 61_r, and servo sector 44 with identification information t is recorded as 44_t. Estimated value c t (r) is an estimated value for the DC pitch variation relative to servo sector 44_t and data track 61_r.

[0091] As shown in mathematical formula 2, the estimated value c t (r) Employs amplitude information |Vavg(n)|, phase information Φavg(n), and servo target position information G. t (r) is used to represent this. That is, as shown in mathematical formulas 1 and 2, the estimated value c... t (r) is the order n of the estimated object, such that it is related to the servo target position information G. t The coefficients corresponding to the phase information Φavg(n) are applied to the correction value of the radial spectrum |Aavg(n)| of the circumferential position CP1 to estimate the DC spacing variation of the circumferential position CP2.

[0092] The phase information Φavg(n) represents the phase of the sine wave corresponding to the circumferential position, expressed as the order n of the variation with respect to the DC spacing. The phase can be the average of the phase corresponding to the circumferential position CP1_1 (e.g., the 0 / 4 circumference position) and the phase corresponding to the circumferential position CP1_2 (e.g., the 2 / 4 circumference position).

[0093] Servo target position information G t (r) can be given by the following mathematical expression 3.

[0094]

[0095] In mathematical formula 3, g avg (r) represents the servo target position relative to data track 61_r. The servo target position can be the average of the servo target position corresponding to circumferential position CP1_1 and the servo target position corresponding to circumferential position CP1_2. g avg (0) indicates the servo target position relative to data track 61_0. g avg (N-1) represents the servo target position relative to data track 61_(N-1).

[0096] As shown in mathematical formula 3, the servo target position information G t (r) is the servo target position corresponding to servo sector 44_t and data track 61_r, expressed as g avg It is represented by standardization based on a benchmark.

[0097] As shown in mathematical formulas 1-3, the estimated value c t (r) is the value obtained by projecting the amplitude |Aavg(n)| of the radial spectrum of the correction value of the circumferential position CP1 radially based on the sum of the phase angle relative to the center of disk 11 and the tilt angle corresponding to the servo target position, thereby approximately estimating the DC pitch variation of the circumferential position CP2. The estimated DC pitch variation is called the DC pitch variation estimation value.

[0098] The controller 30 calculates the estimated value c of the DC pitch variation as shown in mathematical formulas 1 to 3. t (r), thus enabling the acquisition Figure 10 The distribution of the estimated values ​​for DC spacing variation is shown in the figure. Figure 10 This is a graph showing the distribution of estimated values ​​for the DC spacing variation relative to the radial and circumferential positions. Figure 10 In the diagram, the vertical axis represents the radial position, and the horizontal axis represents the circumferential position. Figure 10 The upper side of the middle indicates the inward direction (see reference). Figure 2 ), Figure 10The lower side in the middle indicates the outward direction. The estimated value of the DC spacing variation at each location includes the component estimated for the order n of the estimated object (e.g., n = 25, 28, 45, 70, 79, 87).

[0099] return Figure 6 The controller 30 combines the estimated DC pitch variation value obtained by mathematical formula 2 with the RRO correction value to adjust the RRO correction value (S3).

[0100] For example, the estimated DC pitch variation value calculated using Formula 2 is the value for all servo sectors 44_0 to 44_(MaxSct-1), but the value of servo sector 44 near circumferential position CP2_1 (e.g., 1 / 4 circumference position) and circumferential position CP2_2 (e.g., 3 / 4 circumference position) should be adjusted. Therefore, the controller 30 adjusts the estimated DC pitch variation value c shown in Formula 2. t (r) multiplied by the weighting function w shown in mathematical formula 4 below. t .

[0101] W t =0.8{sin(2πt / MaxSct)} 6 …Mathematical Formula 4

[0102] The weighting function w shown in mathematical formula 4 t This is a function that selectively increases the weight near circumferential positions CP2_1 and CP2_2. Therefore, controller 30 amplifies the estimated value of the servo sector 44 near circumferential positions CP2_1 and CP2_2, while attenuating the estimated value of other servo sectors 44. Equivalently, controller 30 adjusts the estimated value c of the DC pitch variation as shown in Equation 2. t (r) Extract the estimated value of servo sector 44 near circumferential positions CP2_1 and CP2_2.

[0103] For example, controller 30 can control via Figure 11 The DC spacing variation estimate c shown in (a) t The distribution of (r) multiplied by Figure 11 The weighting function w shown in (b) t To get Figure 11 The weighted DC spacing variation estimate is shown in (c). The DC spacing variation estimate includes a component of the order n of the estimated object.

[0104] Figure 11 (a)~ Figure 11 (c) is a graph representing the weighted average of the estimated values ​​for the DC spacing variation. Figure 11 (a) and Figure 10Similarly, this is a graph showing the distribution of estimated DC pitch variations relative to radial and circumferential positions. The estimated DC pitch variations at each position include a component of the order n of the estimated object. Figure 11 (b) represents the weighted function w relative to the circumferential position. t The weights are plotted to show that the weights are selectively large near circumferential positions CP2_1 (e.g., the 1 / 4 circumference position) and circumferential positions CP2_2 (e.g., the 3 / 4 circumference position). Figure 11 (c) is a graph representing the weighted results of the estimated DC pitch variation, showing the distribution of the weighted estimated DC pitch variation relative to the radial and circumferential positions. Figure 11 (c) shows that the estimated DC pitch variation is selectively weighted at circumferential positions CP2_1 and CP2_2.

[0105] In addition, in order to average the original correction value radial spectrum and the DC spacing variation estimate, the controller 30 multiplies the original correction value radial spectrum by the weighting function 1-w of the inverse characteristic for the order n of the estimate object. t The weighting function 1-wt, which is multiplied by the inverse characteristic, is called inverse weighting.

[0106] For example, controller 30 can control via Figure 11 The distribution of the radial spectrum of the RRO correction value shown in (d) is multiplied by Figure 11 The weighted function 1-w of the inverse characteristic shown in (e) t To get Figure 11 The radial spectrum of the inversely weighted RRO correction value is shown in (f).

[0107] Figure 11 (d) Figure 11 (f) is a graph representing the inverse weighting of the radial spectrum of the RRO correction value. Figure 11 (d) and Figure 8 Similarly, this is a graph showing the distribution of the radial spectrum of the RRO correction values ​​relative to the radial and circumferential positions. The radial spectrum of the RRO correction values ​​at each position includes components of each order n. Figure 11 (e) is a weighted function representing the inverse characteristic relative to the circumferential position, 1-w. t The weights are plotted to show that the weights are selectively small near circumferential positions CP2_1 (e.g., the 1 / 4 circumference position) and circumferential positions CP2_2 (e.g., the 3 / 4 circumference position). Figure 11 (f) is a graph showing the result of inverse weighting of the radial spectrum of the RRO correction value, which shows that the components of the radial spectrum of the RRO correction value of each order n are selectively inversely weighted and attenuated at circumferential positions CP2_1 and CP2_2.

[0108] Figure 12The radial spectrum of the inversely weighted RRO correction value shown in (a) is compared with Figure 11 The radial spectrum of the inversely weighted RRO correction value shown in (f) is the same. Controller 30 pairs Figure 12 The radial spectrum of the inversely weighted RRO correction value shown in (a) is subjected to an inverse discrete Fourier transform (inverse DFT) to obtain... Figure 12 The inversely weighted RRO correction value is shown in (b). Figure 12 (b) shows the distribution of the inversely weighted RRO correction values ​​relative to the radial and circumferential positions.

[0109] Figure 13 The distribution of the inversely weighted RRO correction values ​​shown in (a) is similar to Figure 12 The distribution of the inversely weighted RRO correction values ​​shown in (b) is the same. Figure 13 The distribution of the weighted DC spacing variation estimates shown in (b) is similar to Figure 11 The distribution of the weighted DC spacing variation estimate values ​​shown in (c) is the same. Controller 30 will Figure 13 The distribution of the inversely weighted RRO correction values ​​shown in (a) is towards Figure 13 The distribution of the weighted DC spacing variation estimates shown in (b) is synthesized. For example, the controller 30 can synthesize the distribution by using... Figure 13 The distribution of the inversely weighted RRO correction values ​​shown in (a) and Figure 13 The weighted DC spacing variation estimates shown in (b) are summed at two-dimensional locations and then synthesized. Thus, controller 30 can obtain the synthesized RRO correction value as the adjusted RRO correction value. For example, controller 30 can obtain... Figure 13 The distribution of the adjusted RRO correction values ​​is shown in (c). The controller 30 can write the adjusted RRO correction values ​​to the RRO segment 54 of the servo area 42 of each servo sector 44 (see reference). Figure 3 ).

[0110] return Figure 6 Based on the servo information read from the servo track 41, the controller 30 positions the head 22 on the target data track 61 (S4). At this time, the servo information includes the adjusted RRO correction value, so the controller 30 can position the control head 22 with high precision and improve its tolerance to offset writing.

[0111] Offset writing involves writing data with the head 22 offset from the center of the target data track 61. Normally, a write-prohibition process is performed when a certain amount of track offset is detected to prevent data on adjacent data tracks from being erased due to offset writing. However, if there is a DC pitch variation between the servo tracks 41 corresponding to the adjacent data track 61, the correct servo track offset amount will deviate from the offset amount calculated based on the servo pulse train data, potentially resulting in the erasure of adjacent data. In this case, read errors will occur on the adjacent data tracks of the target data track. Therefore, if the DC pitch variation can be corrected, the track offset amount can be accurately detected, and appropriate write prohibition can be performed, thus improving the accuracy of data protection for adjacent data tracks during offset writing of the target data track.

[0112] For example, alternatingly repeating this process 100 times causes head 22 to move from target data track 61-k (refer to...) Figure 5 The number of read errors in the case where data is written and read from the data track 61-(k-1) with a offset from the center of the track, becomes Figure 14 As shown.

[0113] Figure 14 This is a graph representing the characteristics of offset writing. In Figure 14 (a) shows the case where the offset is ΔOF1 (e.g., 1 mm). Figure 14 (b) shows the case where the offset is ΔOF2 (>ΔOF1, for example, 1.5 mm). Figure 14 (c) shows the case where the offset is ΔOF3 (>ΔOF2, for example, 2 mm). Figure 14 (a)~ Figure 14 In (c), the vertical axis represents the number of readout errors, and the horizontal axis represents the circumferential position in disk 11.

[0114] exist Figure 14 (a)~ Figure 14 In (c), as a comparative example, a dashed line indicates the case where positioning control of head 22 is performed using servo information that does not include the adjusted RRO correction value. In this embodiment, a solid line indicates the case where positioning control of head 22 is performed using servo information that includes the adjusted RRO correction value. Figure 14 (a)~ Figure 14As shown in (c), if the offset increases in the order ΔOF1→ΔOF2(>ΔOF1)→ΔOF3(>ΔOF2), then at the circumferential position of 1 / 4 circumference, in the comparative example, a read error occurs from the offset ΔOF1. In contrast, in this embodiment, no read error occurs up to the offset ΔOF2, but a read error only occurs from the offset ΔOF3 onwards. Thus, it is confirmed that this embodiment can improve the tolerance to offset writes compared to the comparative example.

[0115] As described above, in this embodiment, in the disk assembly 1, the controller 30 adjusts the RRO correction value of the servo track 41 based on the ratio of the amplitude of the radial spectrum of the RRO correction value of the servo track 41 at circumferential position CP1 to the amplitude of the radial spectrum of the RRO correction value of the servo track 41 at circumferential position CP2. The circumferential position CP1 can be set as the position where the relative speed of change of the radial position of the servo track 41 with respect to the radial position of the target data track 61 is velocity v1. The circumferential position CP2 can be set as the position where the relative speed of change of the radial position of the servo track 41 with respect to the radial position of the target data track 61 is velocity v2 (< v1). Therefore, compared to the circumferential position CP1, the DC pitch variation at the circumferential position CP2 is less likely to be considered as RRO. In this regard, the controller 30 can estimate the deficiency of the RRO correction value at the circumferential position CP2 based on the RRO correction value at the circumferential position CP1 and make adjustments accordingly. Therefore, in the disk device 1, the adjusted RRO correction value can be used to precisely control the positioning of the head 22, thereby improving the tolerance to offset writing.

[0116] Furthermore, in this embodiment, in the disk assembly 1, the controller 30 determines the order to be adjusted from among the multiple orders included in the pitch variation as the DC pitch variation based on the amplitude ratio of the radial spectrum of the correction value. For the determined order, the controller 30 generates relational information representing the relationship between the radial spectrum of the RRO correction value and the radial position of the servo track 41. The controller 30 uses the relational information to estimate the DC pitch variation of the servo track 41 at the circumferential position CP2. The controller 30 applies a weighted amplification to the estimated DC pitch variation at the circumferential position CP2 and an inverse weighted attenuation to the RRO correction value of the servo track 41 at the circumferential position CP2. The controller 30 synthesizes the inversely weighted RRO correction value and the weighted DC pitch variation to obtain the adjusted RRO correction value. Thus, the controller 30 can estimate and adjust the insufficient RRO correction value at the circumferential position CP2 based on the RRO correction value at the circumferential position CP1.

[0117] For example, consider performing a DFT calculation on the RRO correction values ​​of several data track quantities along the track direction. Significant peaks are treated as DC spacing variations to compensate for the amplitude, thereby adjusting the original RRO correction value. In this case, if the RRO correction value does not have significant peaks, it is difficult to compensate for the amplitude of the DC spacing variation and thus adjust the original RRO correction value.

[0118] In contrast, in this embodiment, the controller 30 can estimate the insufficient amount of the RRO correction value of the circumferential position CP2 based on the RRO correction value of the circumferential position CP1 and make adjustments accordingly. Therefore, even when the RRO correction value does not have a significant peak, the RRO correction value can be adjusted in the disk assembly 1.

[0119] Several embodiments of the present invention have been described, but these embodiments are provided by way of example 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 modifications can be made without departing from the spirit of the invention. These embodiments and / or variations thereof are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

Claims

1. A disk device comprising: head; The disk has multiple servo tracks defined concentrically with respect to a first center, and multiple data tracks defined concentrically with respect to a second center different from the first center; and The controller, when positioning the head on the target data track based on servo information read from the servo track, adjusts the correction value of the radial position of the servo track according to the ratio of the amplitude of the correction value spectrum of the radial position of the servo track at the first circumferential position to the amplitude of the correction value spectrum of the radial position of the servo track at the second circumferential position. At the first circumferential position, the relative velocity of the change in the radial position of the servo track with respect to the radial position of the target data track is the first velocity. At the second circumferential position, the relative velocity of the change in the radial position of the servo track with respect to the radial position of the target data track is the second velocity. At the first circumferential position, the relative velocity of the change in the radial position of the servo track with respect to the radial position of the target data track is the maximum velocity. At the second circumferential position, the relative velocity of the change in the radial position of the servo track with respect to the radial position of the target data track is zero.

2. The disk device according to claim 1, The controller calculates the ratio of the amplitude of the correction value spectrum of the radial position of the servo track at the first circumferential position to the amplitude of the correction value spectrum of the radial position of the servo track at the second circumferential position, based on the multiple order components of the change in the radial position of the servo track relative to the radial position of the target data track, and determines the order of the component to be adjusted based on the calculated ratio.

3. The disk device according to claim 2, The controller generates relational information representing the relationship between the spectrum of the correction value and the radial position of the servo track for the determined order, and uses the relational information to estimate the amount of change in the radial position of the servo track at the second circumferential position.

4. The disk device according to claim 2, The controller applies a first weighting to the estimated variation, amplifying it for the second circumferential position, and applies a second weighting to the correction value of the radial position of the servo track, attenuating it for the second circumferential position. The second weighted correction value and the first weighted variation are combined to obtain the adjusted correction value.

5. The disk device according to claim 1, The controller uses the adjusted correction value to position the head on the target data track.

6. A disk device comprising: head; The disk has multiple servo tracks defined concentrically with respect to a first center, and multiple data tracks defined concentrically with respect to a second center different from the first center; and The controller, when positioning the head on the target data track based on servo information read from the servo track, adjusts the correction value of the radial position of the servo track according to the ratio of the amplitude of the correction value spectrum of the radial position of the servo track at the first circumferential position to the amplitude of the correction value spectrum of the radial position of the servo track at the second circumferential position. The first circumferential position corresponds to the first phase of the periodic change in the radial position of the servo track relative to the radial position of the target data track. The second circumferential position corresponds to the second phase in the periodic change. The periodic changes include sinusoidal variations. The first phase is a 90-degree or 270-degree phase. The second phase is either 0 degrees or 180 degrees.

7. The disk device according to claim 6, The controller calculates the ratio of the amplitude of the correction value spectrum of the radial position of the servo track at the first circumferential position to the amplitude of the correction value spectrum of the radial position of the servo track at the second circumferential position for the components of multiple orders in the periodic change, and determines the order to be adjusted based on the calculated ratio.

8. The disk device according to claim 7, The controller generates relational information representing the relationship between the correction value and the radial position of the servo track for the determined order, and uses the relational information to estimate the amount of change in the radial position of the servo track at the second circumferential position.

9. The disk device according to claim 7, The controller applies a first weighting to the estimated variation, amplifying it for the second circumferential position, and applies a second weighting to the correction value of the radial position of the servo track, attenuating it for the second circumferential position. The second weighted correction value and the first weighted variation are combined to obtain the adjusted correction value.

10. The disk device according to claim 6, The controller uses the adjusted correction value to position the head on the target data track.

11. A disk device comprising: head; The disk has multiple servo tracks defined concentrically with respect to a first center, and multiple data tracks defined concentrically with respect to a second center different from the first center; and The controller, when positioning the head on the target data track based on servo information read from the servo track, adjusts the correction value of the radial position of the servo track based on the amplitude of the correction value spectrum of the radial position of the servo track at the first circumferential position and the amplitude of the correction value spectrum of the radial position of the servo track at the second circumferential position. At the first circumferential position, the relative velocity of the change in the radial position of the servo track with respect to the radial position of the target data track is the maximum velocity. At the second circumferential position, the relative velocity of the change in the radial position of the servo track with respect to the radial position of the target data track is zero.

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