Magnetic disk device and actuator control method

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-036787, filed Mar. 1, 2018, the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a magnetic disk device and an actuator control method.

A magnetic disk device comprises at least one disk and at least one head. If the plurality of disks are vibrated by disturbance or the like, the plurality of heads may be displaced to different positions. Thus, if one of the heads is changed to a different head, the magnetic disk device may have difficulty positioning each of the heads at a particular track.

FIG. 1 is a schematic diagram illustrating an example of a configuration of a magnetic disk device according to a first embodiment.

FIG. 2 is a plan view schematically illustrating an example of a disk.

FIG. 3 is a schematic diagram illustrating an example of a configuration of a tip portion of an arm.

FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2 and illustrating an example of a configuration of an HDA.

FIG. 5 is a cross-sectional view illustrating a state of vibration of the HDA illustrated in FIG. 4 .

FIG. 6 is a diagram illustrating an example of amplitudes corresponding to heads and arms in a case where the HDA is vibrated as illustrated in FIG. 5 .

FIG. 7 is a block diagram illustrating an example of a positioning control system of a two-degree-of-freedom control system according to a first embodiment.

FIG. 8 is block diagram illustrating an example of a disturbance suppression processing system.

FIG. 9 is a diagram illustrating an example of a disturbance suppression process.

FIG. 10 is a diagram illustrating an example of the disturbance suppression process.

FIG. 11 is a flowchart illustrating an example of the disturbance suppression process.

FIG. 12 is a block diagram illustrating an example of a disturbance suppression processing system according to Modification 1.

FIG. 13 is a diagram illustrating an example of a disturbance suppression process according to Modification 1.

FIG. 14 is a flowchart illustrating an example of the disturbance suppression process according to Modification 1.

FIG. 15 is a block diagram illustrating an example of a disturbance suppression processing system according to Modification 2.

FIG. 16 is a diagram illustrating an example of a disturbance suppression process according to Modification 2.

FIG. 17 is a block diagram illustrating an example of a disturbance suppression processing system according to Modification 3.

FIG. 18 is a diagram illustrating an example of a disturbance suppression process according to Modification 3.

FIG. 19 is a diagram illustrating an example of a state of vibration of the heads, the arms, and a VCM in a case where a resonance mode occurs in the HDA according to a second embodiment.

FIG. 20 is a diagram illustrating an example of the state of vibration of the heads, the arms, and the VCM in a case where the resonance mode occurs in the HDA according to the second embodiment.

FIG. 21 is a diagram illustrating an example of amplitudes corresponding to the heads and the arms in a case where the HDA is vibrated as illustrated in FIG. 19 and FIG. 20 .

FIG. 22 is a diagram illustrating an example of the state of vibration of the heads, the arms, and the VCM in a case where the resonance mode according to the second embodiment occurs in the HDA.

FIG. 23 is a diagram illustrating an example of the state of vibration of the heads, the arms, and the VCM in a case where the resonance mode according to the second embodiment occurs in the HDA.

FIG. 24 is a diagram illustrating an example of amplitudes corresponding to the heads and the arms in a case where the HDA is vibrated as illustrated in FIG. 22 and FIG. 23 .

In general, according to one embodiment, a magnetic disk device comprises: a disk comprising a first surface and a second surface opposite to the first surface; a first head configured to execute read/write processing on the first surface; a second head configured to execute read/write processing on the second surface; an actuator configured to position the first head and the second head over the disk; and a controller configured to control the actuator based on a first value having a first waveform suppressing a disturbance component, wherein the controller is configured to invert, in the first waveform, a polarity of a third waveform succeeding a first timing with respect to a polarity of a second waveform preceding the first timing in a case where the first head is changed to the second head at the first timing.

According to another embodiment, a magnetic disk device comprises: a disk comprising a first surface and a second surface opposite to the first surface; a first head configured to execute read/write processing on the first surface; a second head configured to execute read/write processing on the second surface; an actuator configured to position the first head and the second head over the disk; and a controller configured to control the actuator based on a first value suppressing a disturbance component, wherein the controller is configured to adjust the first value based on at least one of a ratio between a first amplitude of the first head and a second amplitude of the second head and correction of phases in a case where the first head is changed to the second head at a first timing.

According to another embodiment, an actuator control method applied to a magnetic disk device comprising a disk comprising a first surface and a second surface opposite to the first surface, a first head configured to execute read/write processing on the first surface, a second head configured to execute read/write processing on the second surface, and an actuator configured to position the first head and the second head over the disk, the actuator control method comprising: controlling the actuator based on a first value having a first waveform suppressing a disturbance component, inverting, in the first waveform, a polarity of a third waveform succeeding a first timing with respect to a polarity of a second waveform preceding the first timing in a case where the first head is changed to the second head at the first timing.

Embodiments will be described below with reference to the drawings. The drawings are illustrative and are not intended to limit the scope of the invention.

First Embodiment

FIG. 1 is a block diagram illustrating a configuration of a magnetic disk device 1 according to a first embodiment.

The magnetic disk device 1 comprises a housing HS, a head disk assembly (HDA) 10 , a driver IC 20 , a head amplifier integrated circuit (hereinafter referred to as the head amplifier IC or preamplifier) 30 , a volatile memory 70 , a buffer memory (buffer) 80 , a nonvolatile memory 90 , and a system controller 130 that is a one-chip integrated circuit. The magnetic disk device 1 is also connected to a host system (hereinafter simply referred to as the host) 100 . FIG. 1 illustrates a cross section of the HDA 10 .

The HDA 10 comprises a magnetic disk (hereinafter referred to as the disk) DK, a spindle motor (hereinafter referred to as the SPM) 13 which rotates the disk DK around a spindle 12 , an arm AM on which a head HD is mounted, and a voice coil motor (hereinafter referred to as the VCM) 14 . The SPM 13 and the VCM 14 are fixed to the housing HS. The disk DK is attached to the spindle 12 and driven and rotated by the SPM 13 . The arm AM and the VCM 14 constitute an actuator AC. The actuator AC controls the position of the head HD. At least one disk DK and at least one head HD are provided.

The disk DK comprises a front surface DKA on which data is recorded and a back surface DKB opposite to the front surface DKA. The back surface DKB faces in a direction opposite to a direction in which the front surface DKA faces. “The front surface DKA and the back surface DKB of the disk DK” may hereinafter collectively be referred to as a “recording surface”. In the example illustrated in FIG. 1 , the disk DK includes a disk DK 0 and a disk DK 1 . The disk DK 0 comprises a front surface DK 0 A and a back surface DK 0 B opposite to the front surface DK 0 A. The disk DK 1 comprises a front surface DK 1 A and a back surface DK 1 B opposite to the front surface DK 1 A. The disk DK may include only one disk or three or more disks.

FIG. 2 is a plan view schematically illustrating an example of the disk DK. A first direction X, a second direction Y, and a third direction Z are orthogonal to one another but may intersect one another in a state other than the orthogonal state. A direction toward a tip of an arrow indicating the third direction Z is referred to as an upper side, and a direction opposite to the tip of the arrow indicating the third direction Z is referred to as a lower side. Furthermore, a length in the first direction may be referred to as a width.

The disk DK includes areas reserved as a user data area UA available to a user and a system area SA to which information needed for system management is written. In the example illustrated in FIG. 2 , the user data area UA 0 and the system area SA 0 are reserved in the front surface DK 0 A. A direction orthogonal to a radial position of the disk DK is hereinafter referred to as the circumferential direction. In the radial position, a direction toward the spindle 12 is referred to as an inner side, and a direction opposite to the inner side is referred to as an outer side.

The head HD is attached to a tip portion of the arm extending from the VCM 14 . The head HD lies opposite to the recording surface of the disk DK. In the example illustrated in FIG. 1 , the head HD includes a head HD 0 , a head HD 1 , a head HD 2 , and a head HD 3 . The arm AM includes an arm AM 0 , an arm AM 1 , an arm AM 2 , and an arm AM 3 . The head HD 0 is attached to a tip portion of the arm AM 0 extending from the VCM 14 toward the front surface DK 0 A of the disk DK 0 . The head HD 1 is attached to a tip portion of the arm AM 1 extending from the VCM 14 toward the back surface DK 0 B of the disk DK 0 . The head HD 2 is attached to a tip portion of the arm AM 2 extending from the VCM 14 toward the front surface DK 1 A of the disk DK 1 . The head HD 3 is attached to a tip portion of the arm AM 3 extending from the VCM 14 toward the back surface DK 1 B of the disk DK 1 . The head HD 0 lies opposite to the front surface DK 0 A of the disk DK 0 . The head HD 1 lies opposite to the back surface DK 0 B of the disk DK 0 . The head HD 2 lies opposite to the front surface DK 1 A of the disk DK 1 . The head HD 3 lies opposite to the back surface DK 1 B of the disk DK 1 . The head HD 0 lies opposite to the head HD 1 via the disk DK 0 . The head HD 2 lies opposite to the head HD 3 via the disk DK 1 . In other words, the direction in which the heads HD 0 and HD 2 face is opposite to the direction in which the heads HD 1 and HD 3 face. The head HD 0 and the head HD 2 face in the same direction. The head HD 1 and the head HD 3 face in the same direction. The “head HD lying opposite to the front surface DKA of the disk DK” may hereinafter be referred to as the “front surface head HDs”, and the “head HD lying opposite to the back surface DKB” may hereinafter be referred to as the “back surface head HDb”. In the example illustrated in FIG. 1 , the front surface head HDs includes the heads HD 0 and HD 2 , and the back surface head HDb includes the heads HD 1 and HD 3 . The head HD may include only one head or three or more heads. The arm AM may include only one arm or three or more arms.

Furthermore, the head HD is driven by the actuator AC (for example, the VCM 14 ) and placed at a particular position on the recording surface of the disk DK. In the example illustrated in FIG. 2 , the head HD 0 is rotationally driven by the VCM 14 and placed at a particular position on the front surface DK 0 A of the disk DK 0 .

FIG. 3 is a schematic diagram illustrating an example of a configuration of the tip portion of the arm AM. The head HD comprises a slider SD as a main body and a magnetic head unit MH mounted on the slider SD opposite to the disk DK. The magnetic head unit MH writes data to the disk DK and reads data from the disk DK. The magnetic head unit MH writes data to a particular position on the opposite recording surface and reads data from a particular position on the opposite recording surface. The magnetic head unit MH comprises a write head and a read head. The write head writes data onto the disk DK. The read head reads data recorded in data tracks on the disk DK. The head HD is attached to a gimbal GB provided at the tip of the arm AM. The head HD is movable using, as a support, a dimple DIP formed like a hemisphere. The dimple DIP is attached to a load beam extending from a lift tab LT. The dimple DIP lies opposite to the position of the gimbal GB.

FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2 and illustrating an example of a configuration of the HDA 10 , and FIG. 5 is a cross-sectional view illustrating an example of a state of vibration of the HDA 10 illustrated in FIG. 4 . FIG. 4 and FIG. 5 illustrate only needed components. In FIG. 4 and FIG. 5 , the housing HS extends in a first direction X, the spindle 12 and the SPM 13 extend in a third direction Z, and the disk DK extends from the spindle 12 toward the first direction X.

If the HDA 10 is not vibrated, the plurality of heads HD are placed in tandem on an axis AX extending in the third direction Z as illustrated in FIG. 4 . In the example illustrated in FIG. 4 , the center of width of each of the heads HD 0 to HD 3 is positioned on the axis AX. In other words, the heads HD 0 to HD 3 lie in tandem on the axis AX. The head HD 0 lies opposite to a position on the front surface DK 0 A which is located on the axis AX. The head HD 1 lies opposite to a position on the back surface DK 0 B which is located on the axis AX. The head HD 2 lies opposite to a position on the front surface DK 1 A which is located on the axis AX. The head HD 3 lies opposite to a position on the back surface DK 1 B located on the axis AX. If the HDA 10 is vibrated by disturbance or the like, each of the plurality of heads HD may be displaced from a target position on the disk DK (hereinafter referred to as the target position) because the head HD is movable using, as a support, the dimple DIP illustrated in FIG. 3 . If the HDA 10 is vibrated at a particular low frequency, for example, 0 to 500 Hz, the plurality of disks DK may be vibrated at the same amplitude and toward the same side in the third direction Z. Here, the term “same” includes not only the perfect sameness of two or more target physical quantities but also such a difference between the two or more physical quantities as allows the physical quantities to be considered to be substantially the same. The “vibration at the same amplitude and toward the same side” as described above is expressed as “synchronous vibration”. A “phenomenon in which the plurality of disks DK are synchronously vibrated as a result of vibration of the HDA 10 at a particular low frequency” is hereinafter referred to as the “synchronous resonance mode”. The synchronous resonance mode may be referred to as a drum mode.

If the synchronous resonance mode occurs, the plurality of disks DK are synchronously vibrated. In this case, the plurality of heads HD are vibrated in response to vibration of the plurality of disks DK. The front surface heads HDs included in the plurality of heads HD are displaced toward the same side with respect to the front surface DKA. The back surface heads HDb of the plurality of heads HD are displaced toward the same side with respect to the back surface DKB. The front surface heads HDs are displaced toward the side opposite to the side toward which the back surface heads HDb are displaced. In the example illustrated in FIG. 5 , the disk DK 0 and the disk DK 1 are vibrated synchronously in the third direction Z due to the synchronous resonance mode. The disk DK 0 and the disk DK 1 are inclined obliquely upward from the inner side toward the outer side. The head HD 0 is inclined obliquely upward from the inner side toward the outer side along the front surface DK 0 A. Thus, the head HD 0 is displaced to a position on the outer side of the position on the front surface DK 0 A located on the axis AX. The head HD 1 is inclined obliquely downward from the outer side toward the inner side along the back surface DK 0 B. Thus, the head HD 1 is displaced to a position on the inner side of the position on the front surface DK 0 B located on the axis AX. The head HD 2 is inclined obliquely upward from the inner side toward the outer side along the front surface DK 1 A. Thus, the head HD 2 is displaced to a position on the outer side of the position on the front surface DK 1 A located on the axis AX. The head HD 3 is inclined obliquely downward from the outer side toward the inner side along the back surface DK 1 B. Thus, the head HD 3 is displaced to a position on the inner side of the position on the back surface DK 1 B located on the axis AX. The head HD 0 and the head HD 2 are displaced toward the same side. The head HD 1 and the head HD 3 are displaced toward the same side.

FIG. 6 is a diagram illustrating an example of amplitudes corresponding to the heads HD and the arms AM in a case where the HDA 10 is vibrated as illustrated in FIG. 5 . In FIG. 6 , the ordinate axis indicates the amplitude, and the abscissa axis indicates the heads HD and the arms AM corresponding to the respective amplitudes. In FIG. 6 , the amplitudes corresponding to the heads HD and the arms AM are each normalized using a particular value. Thus, in FIG. 6 , the amplitudes corresponding to the heads HD and the arms AM fluctuate between a particular value with a positive polarity, for example, 1, and a particular value with a negative polarity, for example, −1. In FIG. 6 , for the amplitude, the maximum value with the positive polarity is 1, and the maximum value with the negative polarity is −1. Here, the negative polarity is opposite to the positive polarity.

As illustrated in FIG. 5 , if the synchronous resonance mode occurs, a plurality of amplitudes corresponding to the respective front surface heads HDs have the same polarity. In this case, a plurality of amplitudes corresponding to the respective back surface heads HDb have the same polarity. Furthermore, if the synchronous resonance mode occurs, the polarity of the amplitude corresponding to each front surface head HDs is opposite to the polarity of the amplitude corresponding to each back surface head HDb. In the example illustrated in FIG. 6 , an amplitude AP 60 corresponding to the head HD 0 and the arm AM 0 is the same as an amplitude AP 62 corresponding to the head HD 2 and the arm AM 2 , and an amplitude AP 61 corresponding to the head HD 1 and the arm AM 1 is the same as an amplitude AP 63 corresponding to the head HD 3 and the arm AM 3 . Each of the amplitudes AP 60 and AP 62 has the same magnitude as that of each of the amplitudes AP 61 and AP 63 . The amplitude AP 60 and the amplitude AP 62 have the positive polarity, and the amplitude AP 61 and the amplitude AP 63 have the negative polarity. In other words, the polarity of each of the amplitude AP 60 and the amplitude AP 62 is opposite to the polarity of each of the amplitude AP 61 and the amplitude AP 63 .

The driver IC 20 controllably drives the SPM 13 and VCM 14 under the control of the system controller 130 (specifically, the MPU 50 described below). The driver IC 20 comprises an SPM controller 21 and a VCM controller 22 . The SPM controller 21 controls rotation of the SPM 13 . The VCM controller 22 controllably drives the VCM 14 by controlling a supplied current. Functions of the driver 20 may be provided in the system controller 130 .

The head amplifier IC (preamplifier) 30 amplifies a read signal read from the disk DK and outputs the amplified read signal to the system controller 130 (specifically, a read/write (R/W) channel 40 described below). The head amplifier IC 30 also outputs, to the head HD, a write current corresponding to a signal output from the R/W channel 40 . The head amplifier IC 30 comprises a head selector 31 and a signal detector 32 . The head selector 31 selects the head that executes read/write processing, from the plurality of heads HD under the control of the system controller 130 (specifically, the MPU 50 described below). The signal detector 32 detects a signal to be written by the write head and a signal read by the read head. Functions of the head amplifier IC 30 may be provided in the system controller 130 .

The volatile memory 70 is a semiconductor memory from which saved data is lost if power supply is disrupted. The volatile memory 70 stores, for example, data needed for processing in each unit of the magnetic disk device 1 . The volatile memory 70 is, for example, a Dynamic Random Access Memory (DRAM) or a Synchronous Dynamic Random Access Memory (SDRAM).

The buffer memory 80 is a semiconductor memory in which, for example, data transmitted and received between the magnetic disk device 1 and the host 100 is temporarily recorded. The buffer memory 80 may be configured integrally with the volatile memory 70 . The buffer memory 80 is, for example, a DRAM, a Static Random Access Memory (SRAM), an SDRAM, a Ferroelectric Random Access Memory (FeRAM), or a Magnetoresistive Random Access Memory.

The nonvolatile memory 90 is a semiconductor memory in which saved data is recorded even if power supply is disrupted. The nonvolatile memory 90 is, for example, a NOR or NAND flash ROM (Flash Read Only Memory: FROM).

The system controller (controller) 130 is implemented using, for example, a large-scale integrated circuit (LSI) referred to as a System-on-a-Chip (SoC) and comprising a plurality of elements integrated together on a single chip. The system controller 130 includes the read/write (R/W) channel 40 , the microprocessor (MPU) 50 , and a hard disk controller (HDC) 60 . The system controller 130 is electrically connected to the driver IC 20 , the head amplifier IC 30 , the volatile memory 70 , the buffer memory 80 , the nonvolatile memory 90 , and the host system 100 . The system controller 130 may comprise the SPM controller 21 , the VCM controller 22 , the head selector 31 , and the signal detector 32 . Furthermore, the system controller 130 may comprise the driver IC 20 and the head amplifier IC 30 .

The R/W channel 40 executes signal processing on read data transferred from the disk DK to the host 100 and on write data transferred from the host 100 , in accordance with instructions from the MPU 50 , described below. The R/W channel 40 comprises a circuit or a function to measure signal quality of read data. The R/W channel 40 is electrically connected to, for example, the head amplifier IC 30 , the MPU 50 , and the HDC 60 .

The MPU 50 is a main controller controlling each unit of the magnetic disk device 1 in accordance with instructions from the host 100 and the like. The MPU 50 controls the actuator AC via the driver IC 20 to perform servo control for positioning the head HD. The MPU 50 controls an operation of writing data to the disk DK and selects a destination to which write data is to be saved. The MPU 50 also controls an operation of reading data from the disk DK and controllably process read data. The MPU 50 is connected to each unit of the magnetic disk device 1 . The MPU 50 is electrically connected to, for example, the driver IC 20 , the R/W channel 40 , and the HDC 60 .

The HDC 60 controls the read/write processing and data transfer between the host 100 and the R/W channel 40 , in accordance with instructions from the MPU 50 . The HDC 60 is electrically connected to, for example, the R/W channel 40 , the MPU 50 , the volatile memory 70 , the buffer memory 80 , and the nonvolatile memory 90 .

The HDC 60 comprises a head controller 61 and a servo controller 62 . The HDC 60 causes these units, for example, the head controller 61 and the servo controller 62 to execute respective types of processing on firmware. The HDC 60 may comprise these units as a circuit. Furthermore, the functions of the HDC 60 may be provided in the MPU 50 . For example, the head controller 61 and the servo controller 62 may be provided in the MPU 50 .

The head controller 61 controls the head HD that executes the read/write processing. The head controller 61 selects, via the head selector 31 , the head HD that executes the read/write processing. The head controller 61 changes the head HD that executes the read/write processing. “Changing the head HD that executes the read/write processing” may be referred to as “head change”. To perform a head change, the head controller 61 outputs a signal for a head change to the servo controller 62 described below. If the head HD currently executing the read/write processing (hereinafter referred to as the current head) faces in the direction opposite to the direction in which the head HD to which the current head is to be changed (hereinafter referred to as the next head) faces, the head controller 61 outputs a signal, for example, a flag, which indicates that the current head HD and the next head HD face in the opposite directions (hereinafter referred to as the opposite flag). For example, if the front surface head HDs is changed to the back surface head HDb, the head controller 61 outputs the opposite flag. The head controller 61 also controllably moves the head HD to a particular radial position on the disk DK. If the head HD starts seeking, the head controller 61 outputs, to the servo controller 62 , a signal, for example, a flag, which causes the head HD to start seeking (hereinafter referred to as the start flag).

The servo controller 62 controllably places the head HD at a particular position on the disk DK under the control of the head controller 61 . The servo controller 62 comprises a tracking controller 621 , a seek controller 622 , and a disturbance controller 623 .

The tracking controller 621 controllably causes the head HD to follow a particular position, for example, a particular track, on the disk during the read/write processing.

The seek controller 622 controls seeking by the head HD. If the seek controller 622 , for example, receives the start flag from the head controller 61 , the seek controller 622 causes the head HD to start seeking.

The disturbance controller 623 executes a process (hereinafter referred to as the disturbance suppression process) for suppressing adverse effects of disturbance and the like (hereinafter referred to as the disturbance component) on driving by the actuator AC, positioning of the head HD, and the like. For example, the disturbance controller 623 executes a loop shaping process to suppress adverse effects of various types of vibration, for example, the synchronous resonance mode, on driving by the actuator AC, positioning of the head HD, and the like.

FIG. 7 is a block diagram illustrating an example of a positioning control system SY 1 of a two-degree-of-freedom control system according to the first embodiment. FIG. 7 illustrates a control system performing feed-forward seek.

The magnetic disk device 1 comprises a plant control system (positioning control system) SY 1 for positioning the head HD. The positioning control system SY 1 comprises a state estimation unit S 1 , a disturbance suppression unit S 2 , a plant controller S 3 , a plant S 4 , and calculation units C 1 , C 2 , and C 3 . In an example, the state estimation unit S 1 , the disturbance suppression unit S 2 , the plant controller S 3 , and the calculation units C 1 to C 3 are provided in the servo controller 62 . The plant S 4 corresponds to, for example, the head HD and the actuator AC. The positioning control system SY 1 performs feedback control for the two-degree-of-freedom control system.

The state estimation unit S 1 is a state observer comprising a model of the plant S 4 (hereinafter referred to as the plant model) and an internal state variable. The state estimation unit S 1 estimates a target position (hereinafter referred to as the estimated position) Psm of the plant S 4 on the disk DK in a sample of servo next to the current servo of the plant S 4 (hereinafter referred to as the next sample) based on the plant model, the internal state variable, a driving amount U for the plant S 4 (hereinafter referred to as the actual driving amount U), and the position P of the plant S 4 on the current disk DK (hereinafter referred to as the actual position P). The state estimation unit S 1 calculates an error (hereinafter referred to as the model position error) Epm between the actual position P and the position of the plant S 4 in the plant model corresponding to the actual position P based on the plant model, the internal state variable, the actual driving amount U, and the actual position P. The state estimation unit S 1 performs observer control to prevent an increase in model position error Epm and updates the internal state variable for each sample of servo for the plant S 4 .

The disturbance suppression unit S 2 executes a disturbance suppression process, for example, a loop shaping process. The disturbance suppression unit S 2 generates a signal Uls suppressing a disturbance component (hereinafter referred to as the suppression amount Uls) based on the model position error Epm and an error Ep between a target position Ptgt and the estimated position Psm (hereinafter referred to as the estimated position error Ep).

The plant controller S 3 executes a process other than the disturbance suppression process, for example, controls the plant S 4 . The plant controller S 3 , for example, generates a driving amount Uc for the plant S 4 based on the model position error Epm and the estimated position error Ep. The plant controller S 3 may, for example, generate the driving amount Uc based on values other than the model position error Epm and the estimated position error Ep.

The plant S 4 is driven based on the actual driving amount U.

In the HDC 60 , if a particular position on the disk DK is specified from which data is to be read or to which data is to be written (hereinafter referred to as the specified position), the calculation unit C 1 receives a correct position Ptgt_ff which corrects a specified position Ptgt_dc based on feedback control and a specified position Ptgt_dc based on feed-forward control. The correction position Ptgt_ff is, for example, 0 if the head HD is tracking a particular track, and varies over time if the head HD is seeking. The calculation unit C 1 adds the correction position Ptgt_ff to the specified position Ptgt_dc and outputs the resultant target position Ptgt to the calculation unit C 2 .

The state estimation unit S 1 receives the actual driving amount U and the actual position P corresponding to the position of the plant S 4 to which a disturbance Dp is added. The state estimation unit S 1 outputs the estimated position Psm to the calculation unit C 2 , and outputs the model position error Epm to the disturbance suppression unit S 2 and the plant controller S 3 . The calculation unit C 2 receives the target position Ptgt and the estimated position Psm. The calculation unit C 2 reduces the estimated position Psm from the target position Ptgt and outputs the resultant estimated position error Ep to the disturbance suppression unit S 2 and the plant controller S 3 . If the feed-forward control is not performed, the calculation unit C 2 receives, instead of the target position Ptgt, a target speed of the head HD, an estimated speed estimated by the state estimation unit S 1 , and the like. The calculation unit C 2 reduces the estimated speed from the target speed and outputs a resultant estimated speed error to the disturbance suppression unit S 2 and the plant controller S 3 .

The disturbance suppression unit S 2 receives the model position error Epm and the estimated position error Ep. For example, if a head change is performed, the disturbance suppression unit S 2 receives an opposite flag FG 1 and a start flag FG 2 from the head controller 61 . The disturbance suppression unit S 2 outputs the suppression amount Uls to the calculation unit C 3 .

The plant controller S 3 receives the model position error Epm and the estimated position error Ep. The plant controller S 3 outputs the driving amount Uc to the calculation unit C 3 . If the feed-forward control is not performed, the plant controller S 3 receives a target acceleration for the head HD and the like. The calculation unit C 3 receives the driving amount Uc, the suppression amount Uls, and a signal (hereinafter referred to as the correction amount) Uff which corrects the driving amount Uc based on the feed-forward control. The calculation unit C 3 outputs, to the plant S 4 , the actual driving amount U, corresponding to the sum of the driving amount Uc, the suppression amount Uls, and the correction amount Uff. The plant S 4 is driven in accordance with the actual driving amount U to move to the actual position P, that is, the position corresponding to the actual driving amount U and to which the disturbance Dp is added. The actual driving amount U, the driving amount Uc, the suppression amount Uls, and the correction amount Uff correspond to, for example, values of currents driving the VCM 14 .

FIG. 8 is a block diagram illustrating an example of a disturbance suppression processing system SY 2 .

The disturbance suppression unit S 2 comprises the disturbance suppression processing system SY 2 , which executes the disturbance suppression process. The disturbance suppression system SY 2 comprises a gain G 1 , a gain G 2 , a filter FT, and a saving area SR 1 . The saving area SR 1 may be, for example, a memory.

The gain G 1 receives the estimated position error Ep. The gain G 1 multiplies the estimated position error Ep by a variable gain to output the result to the filter FT and the saving area SR 1 . The gain G 2 receives the model position error Epm. The gain G 2 multiplies the model position error Epm by a variable gain to output the result to the filter FT and the saving area SR 1 .

The filter FT includes a coefficient which suppresses a particular frequency component of an input signal. The filter FT generates the current suppression amount Uls by executing the disturbance suppression process, for example, the loop shaping process, based on the currently input estimated position error Ep, the currently input model position error Epm, a previously input estimated position error Ep, a previously input model position error Epm, a previously output suppression amount Uls, and the like. The “currently input estimated position error” is hereinafter referred to as the “current estimated position error”, the “currently input model position error” is hereinafter referred to as the “current model position error”, the “previously input estimated position error” is hereinafter referred to as “previous estimated position error”, the “previously input model position error” is hereinafter referred to as the “previous model position error”, and the “previously output suppression amount” is hereinafter referred to as the “previous suppression amount”. For convenience of description, the “previous estimated position error” and the “previous model position error” may hereinafter be collectively referred to as the “past input values”, and the “previous suppression amount” may hereinafter be referred to as the “past output value”. Furthermore, the “past input values”, and “previous suppression amount” may hereinafter be collectively referred to as the “past values”. The filter FT outputs the current suppression amount Uls to the saving area SR 1 and the calculation unit C 3 illustrated in FIG. 7 . The filter FT is a loop shaping filter, for example, a finite impulse response (FIR) filter or an infinite impulse response (IIR) filter.

The saving area SR 1 has the past values recorded therein. The saving area SR 1 outputs the past values to the filter FT. If the opposite flag FG 1 and the start flag FG 2 are input to the saving area SR 1 , the saving area SR 1 inverts the polarities of the past values to output the resultant values to the filter FT. For example, if the filter FT is an IIR filter and the opposite flag FG 1 and the start flag FG 2 are input to the saving area SR 1 , the saving area SR 1 inverts the polarities of the past input values to output the resultant values to the filter FT. Furthermore, if the filter FT is an FIR filter and the opposite flag FG 1 and the start flag FG 2 are input to the saving area SR 1 , the saving area SR 1 inverts the polarities of the past input values to output the resultant values to the filter FT. In other words, if the opposite flag FG 1 and the start flag FG 2 are input to the saving area SR 1 , the saving area SR 1 multiples the past values by the ratio of the amplitude of the front surface head HDs to the amplitude of the back surface head HDb or the ratio (gain) of the amplitude of the back surface head HDb to the amplitude of the front surface head HDs to output the resultant values to the filter FT. In an example, if the opposite flag FG 1 and the start flag FG 2 are input to the saving area SR 1 , the saving area SR 1 multiples the past values by the ratio (−1) of an amplitude AP 60 (1) of the front surface head HD 0 to an amplitude AP 61 (−1) of the head HD 1 , illustrated in FIG. 6 , and outputs the resultant values to the filter FT. The saving area SR 1 is capable of outputting past values with waveforms with particular phases. For example, when a head change is performed, and if a phase shift occurs between a waveform preceding the head change and a waveform succeeding the head change, the saving area SR 1 may output, to the filter FT, past values with shifted phases corresponding to the phase shift having occurred.

FIG. 9 is a diagram illustrating an example of the disturbance suppression process. In FIG. 9 , the abscissa axis indicates time. In FIG. 9 a driving amount Ub indicates a current value corresponding to a driving amount of the plant S 4 which is equal to the actual driving amount U from which the suppression amount Uls is excluded. As illustrated in FIG. 9 , the suppression amount Uls has a waveform WV 0 which suppresses disturbance components. In the example illustrated in FIG. 9 , the waveform WV 0 is a sine wave having a constant amplitude and a constant wavelength. FIG. 9 illustrates variable gains applied by the gain G 1 and the gain G 2 illustrated in FIG. 8 . For convenience of description, the variable gains applied by the gain G 1 and the gain G 2 may be respectively referred to as the gain G 1 and the gain G 2 . In FIG. 9 , a timing Tch 0 indicates a timing when the head HD 0 is changed to the head HD 2 , a timing Ti 1 indicates a timing when the head HD 2 starts settling at a particular track, and a timing Ti 2 indicates a timing when the head HD 2 completes settling at the particular track.

In the example illustrated in FIG. 9 , if the system controller 130 changes the head HD 0 to the head HD 2 at the timing Tch 0 , the system controller 130 starts causing the head HD 2 to seek a particular track at the timing Tch 0 . The system controller 130 starts increasing the driving amount Ub at the timing Tch 0 to accelerate the head HD 2 , and reduces the driving amount Ub over time to decelerate the head HD 2 consistently with the distance to the particular track. The system controller 130 multiplies the model position error Epm by the gain G 2 , for example, 1. The system controller 130 multiplies the estimated position error Ep by a gain G 1 of 0 from the timing Tch 0 through the timing Ti 1 and multiplies, from the timing Ti 1 through the timing Ti 2 , by a gain G 1 increasing from 0 to 1 over time. The system controller 130 also suppresses the disturbance components using the suppression amount Uls with the waveform WV 0 .

FIG. 10 is a diagram illustrating an example of the disturbance suppression process. In FIG. 10 , the timing Tch 1 indicates a timing when the head HD 0 is changed to the head HD 1 .

In the example illustrated in FIG. 10 , if the system controller 130 changes the head HD 1 to the head HD 0 at the timing Tch 1 , the system controller 130 causes the head HD 2 to start seeking a particular track at the timing Tch 1 . In the waveform WV 0 of the suppression amount Uls, the system controller 130 inverts the polarity of a waveform WV 2 succeeding the timing Tch 1 (hereinafter referred to as the succeeding waveform WV 2 ) with respect to the polarity of a waveform WV 1 preceding the timing Tch 1 (hereinafter referred to as the preceding waveform WV 1 ). In other words, the system controller 130 multiplies the suppression amount Uls succeeding the timing Tch 1 by the ratio (−1) of the amplitude (1) of the head HD 0 to the amplitude (−1) of the head HD 1 , illustrated in FIG. 6 . The system controller 130 outputs the suppression amount Uls with the succeeding waveform WV 2 that is discontinuous with the preceding waveform WV 1 . If, with the synchronous resonance mode occurring, the front surface head HDs is changed to the back surface head HDb or the back surface head HDb is changed to the front surface head HDs, the system controller 130 can suppress the adverse effects of the synchronous resonance mode during seeking by the next head HD by inverting the succeeding waveform WV 2 as illustrated in FIG. 10 .

FIG. 11 is a flowchart illustrating an example of the disturbance suppression process.

The system controller 130 causes the head HD to track a particular track in accordance with an instruction from the host 100 (B 1101 ). The system controller 130 determines whether or not to perform a head change (B 1102 ). In a case of not performing a head change (NO in B 1102 ), the system controller 130 proceeds to processing in B 1105 . In a case of performing a head change (B 1102 ), the system controller 130 determines whether or not the next head faces in the direction opposite to the direction in which the current head HD faces (B 1103 ). In a case of determining that the next head does not face in the direction opposite to the direction in which the current head HD faces (NO in B 1103 ), the system controller 130 proceeds to processing in B 1105 . In a case of determining that the next head faces in the direction opposite to the direction in which the current head HD faces (YES in B 1103 ), the system controller 130 inverts the polarity of the succeeding waveform WV 2 ( 31104 ). The system controller 130 causes the head HD to seek a particular track (B 1105 ), and ends the process.

According to the present embodiment, if the next head HD faces in the direction opposite to the direction in which the current head HD faces, the magnetic disk device 1 inverts the polarity of the succeeding waveform WV 2 . Thus, if, with the synchronous resonance mode occurring, the front surface head HDs is changed to the back surface head HDb or the back surface head HDb is changed to the front surface head HDs, the system controller 130 can suppress the adverse effects of the synchronous resonance mode during seeking by the next head HD by inverting the succeeding waveform WV 2 . Therefore, the magnetic disk device 1 is capable of improving the accuracy of the servo control.

Now, magnetic disk devices according to modifications and other embodiments will be described. In the modifications and the other embodiments, the same components as those of the above-described embodiment are denoted by the same reference numerals and will not be described in detail.

(Modification 1)

The magnetic disk device 1 according to Modification 1 is different from the magnetic disk device 1 according to the above-described embodiment in the configuration of the disturbance suppression system SY 2 .

FIG. 12 is a block diagram illustrating an example of the disturbance suppression system SY 2 according to Modification 1.

The disturbance suppression system SY 2 further comprises a gain G 3 , a gain G 4 , a saving area SR 2 , and a calculation unit C 4 . The saving area SR 2 may be, for example, a memory.

The filter FT calculates and outputs a suppression amount Uls 0 to the saving area SR 1 , the gain G 3 , and the saving area SR 2 . The suppression amount Uls 0 corresponds to the suppression amount Uls illustrated in FIG. 8 . The gain G 3 receives the suppression amount Uls 0 . The gain G 3 multiplies the suppression amount Uls 0 by the variable gain to output a resultant suppression amount Uls 1 to the calculation unit C 4 .

The saving area SR 2 has the suppression amount Uls 0 and the like recorded therein. If the start flag FG 2 is input to the saving area SR 2 , the saving area SR 2 outputs, to the gain G 4 , the suppression amount Uls 0 at the timing of a head change, that is, the timing of the start of seeking by next head HD. The gain G 4 multiplies, by the variable gain, the suppression amount Uls 0 at the timing of the head change to output a resultant suppression amount Uls 2 to the calculation unit C 4 . The calculation unit C 4 adds the suppression amount Uls 2 to the suppression amount Uls 1 to output the resultant suppression amount Uls to the calculation unit C 3 illustrated in FIG. 7 .

FIG. 13 is a diagram illustrating an example of a disturbance suppression process according to Modification 1. The driving amount Ub, the gain G 1 , and the gain G 2 are the same as those in FIG. 10 and are thus omitted from FIG. 13 . FIG. 13 illustrates the start flag FG 2 illustrated in FIG. 12 . If the start flag FG 2 has a value of larger than 0 (hereinafter referred to as High), seeking by the next head is started. FIG. 13 illustrates a flag FG 3 . The flag FG 3 specifies a period (hereinafter referred to as the switching time) dT when a process (hereinafter referred to as the continuous-waveform process) is executed such that the waveform WV 1 of the suppression amount Uls 0 preceding the waveform WV 0 thereof is continuous with the waveform WV 2 of the suppression amount Uls 0 succeeding the waveform WV 0 . Here, two continuous waveforms include not only two connected waveforms but also two waveforms which are discontinuous to the degree that the waveforms are considered to be substantially connected together. If the flag FG 3 is High, the continuous-waveform process is executed. If the flag FG 3 is 0 (hereinafter referred to as Low), the continuous-waveform process is not executed. The switching time dT may be optionally determined based on a seek condition for the next head HD such as a seek distance or a seek speed or may be recorded in the memory, for example, the nonvolatile memory 90 , as a table in accordance with the seek condition. FIG. 13 illustrates variable gains applied by the gain G 3 and the gain G 4 illustrated in FIG. 12 . For convenience of description, the variable gains applied by the gain G 3 and the gain G 4 may be respectively referred to as the gain G 3 and the gain G 4 .

In the example illustrated in FIG. 13 , at the timing Tch 1 , when the start flag FG 2 is High, the system controller 130 changes the head HD 1 to the head HD 0 to cause the head HD 0 to start seeking. For the waveform WV 0 of the suppression amount Uls 0 , the system controller 130 inverts the polarity of the succeeding waveform WV 2 of the suppression amount Uls 0 . The system controller 130 executes the continuous-waveform process on the preceding waveform WV 1 and the succeeding waveform WV 2 during the switching time dT from the timing Tch 1 until a timing To 1 when the start flag FG 2 is Low. The system controller 130 generates the suppression amount Uls 1 by multiplying the succeeding waveform WV 2 by the gain G 3 increasing, for example, from 0 to 1 over time during the switching time dT. The system controller 130 generates the suppression amount Uls 2 by multiplying the amplitude A 1 of the preceding waveform WV 1 at the timing Tch 1 by the gain G 4 decreasing, for example, from 1 to 0 over time during the switching time dT. The system controller 130 adds the suppression amount Uls 2 to the suppression amount Uls 1 to generate the suppression amount Uls including the preceding waveform WV 1 and the succeeding waveform WV 2 continuous with each other.

FIG. 14 is a flowchart illustrating an example of a disturbance suppression process according to Modification 1.

The system controller 130 causes the head HD to track a particular track (B 1101 ), determines whether or not to perform a head change (B 1102 ), determines whether or not the next head faces in the direction opposite to the direction in which the current head HD faces (B 1103 ), and inverts the polarity of the succeeding waveform WV 2 (B 1104 ). The system controller 130 executes the continuous-waveform process on the suppression amount Uls 0 (B 1401 ). For example, the system controller 130 generates the suppression amount Uls 1 by multiplying the succeeding waveform WV 2 by the gain G 3 increasing, for example, from 0 to 1 over time during the switching time dT. The system controller 130 generates the suppression amount Uls 2 by multiplying the amplitude A 1 of the preceding waveform WV 1 at the timing Tch 1 by the gain G 4 decreasing, for example, from 1 to 0 over time during the switching time dT. The system controller 130 adds the suppression amount Uls 2 to the suppression amount Uls 1 to generate the suppression amount Uls including the preceding waveform WV 1 and the succeeding waveform WV 2 continuous with each other. The system controller 130 causes the head HD to seek a particular position (B 1105 ) to end the process.

According to Modification 1, if the next head HD faces in the direction opposite to the direction in which the current head faces, the magnetic disk device 1 can invert the polarity of the succeeding waveform WV 2 to adjustably make the preceding waveform WV 1 continuous with the succeeding waveform WV 2 . The magnetic disk device 1 generates the suppression amount Uls 1 by multiplying the succeeding waveform WV 2 by the gain G 3 increasing over time during the switching time dT and generates the suppression amount Uls 2 by multiplying the amplitude A 1 of the preceding waveform WV by the gain G 4 decreasing over time during the switching time dT. The magnetic disk device 1 is capable of adding the suppression amount Uls 2 to the suppression amount Uls 1 to output the suppression amount Uls comprising the waveform WV 0 including the preceding waveform WV 1 and the succeeding waveform WV 2 continuous with each other. In other words, the magnetic disk device 1 is capable of inverting the polarity of the succeeding waveform WV 2 to output the suppression amount Uls including the preceding waveform WV 1 and the succeeding waveform WV 2 smoothly connected together. Thus, the magnetic disk device is capable of preventing a rapid change in acceleration and jerk of the head HD immediately after a head change.

(Modification 2)

The magnetic disk device 1 according to Modification 2 is different from the magnetic disk device according to the above-described embodiment in the configuration of the disturbance suppression processing system SY 2 .

FIG. 15 is a block diagram illustrating an example of the disturbance suppression processing system SY 2 according to Modification 2.

Compared to the disturbance suppression processing system SY 2 illustrated in FIG. 12 , the disturbance suppression processing system SY 2 according to Modification 2 does not comprise the saving area SR 2 .

The filter FT calculates and outputs the suppression amount Uls 0 to the gain G 3 and the gain G 4 . The gain G 3 receives the suppression amount Uls 0 . The gain G 3 multiplies the suppression amount Uls 0 by the variable gain to output the resultant suppression amount Uls 1 to the calculation unit C 4 . The gain G 4 receives the suppression amount Uls 0 . The gain G 4 multiplies the suppression amount Uls 0 by the variable gain to output resultant suppression amount Uls 2 to the calculation unit C 4 . The calculation unit C 4 adds the suppression amount Uls 2 to the suppression amount Uls 1 to output the resultant suppression amount Uls to the calculation unit C 3 illustrated in FIG. 7 .

FIG. 16 is a diagram illustrating an example of a disturbance suppression process according to Modification 2. The driving amount Ub, the gain G 1 , and the gain G 2 are the same as those in FIG. 10 and are thus omitted from FIG. 16 .

In the example illustrated in FIG. 16 , the system controller 130 generates the suppression amount Uls 2 by multiplying, by the gain G 4 increasing from −1 to 0 over time, a partial waveform WV 21 of the succeeding waveform WV 2 corresponding to the switching time dT. In other words, the system controller 130 generates the suppression amount Uls 2 by inverting the polarity of the waveform WV 21 and multiplying the waveform WV 21 by the gain G 4 increasing, for example, from 0 to 1 over time during the switching time dT. The system controller 130 adds the suppression amount Uls 2 to the suppression amount Uls 1 to generate the suppression amount Uls including the preceding waveform WV 1 and the succeeding waveform WV 2 continuous with each other.

According to Modification 2, the magnetic disk device is capable of outputting, using the simple configuration, the suppression amount Uls comprising the waveform WV 0 including the preceding waveform WV 1 and the succeeding waveform WV 2 continuous with each other.

(Modification 3)

The magnetic disk device 1 according to Modification 3 is different from the magnetic disk device according to the above-described embodiment in the configuration of the disturbance suppression processing system SY 2 .

FIG. 17 is a block diagram illustrating an example of the disturbance suppression processing system SY 2 according to Modification 3.

Compared to the disturbance suppression processing system SY 2 illustrated in FIG. 15 , the disturbance suppression processing system SY 2 according to Modification 3 does not comprise the gain G 4 or the calculation unit C 4 .

The filter FT calculates and outputs the suppression amount Uls 0 to the gain G 3 . The gain G 3 receives the suppression amount Uls 0 . The gain G 3 multiplies the suppression amount Uls 0 by the variable gain to output the resultant suppression amount Uls to the calculation unit C 3 illustrated in FIG. 7 .

FIG. 18 is a diagram illustrating an example of a disturbance suppression process according to Modification 3. The driving amount Ub, the gain G 1 , and the gain G 2 are the same as those in FIG. 10 and are thus omitted from FIG. 18 .

In the example illustrated in FIG. 18 , the system controller 130 generates the suppression amount Uls by multiplying the succeeding waveform WV 2 by the gain G 3 varying from a particular value with a negative polarity to a particular value with a positive polarity, for example, −1 to 1, over time during the switching time dT. In other words, the system controller 130 generates the suppression amount Uls by inverting the polarity of the succeeding waveform WV 2 during the switching time dT to multiply the succeeding waveform WV 2 by the gain increasing, for example, from −1 to 0 over time during the switching time dT and the gain increasing, for example, from 0 to 1 over time during the switching time dT.

According to Modification 3, the magnetic disk device is capable of outputting, using the simple configuration, the suppression amount Uls comprising the waveform WV 0 including the preceding waveform WV 1 and the succeeding waveform WV 2 continuous with each other.

Second Embodiment

The magnetic disk device 1 according to a second embodiment is different from the magnetic disk device according to the above-described embodiment in the configuration that can be applied if a resonance mode other than the synchronous resonance mode occurs.

The system controller 130 comprises a function to correct, for a head change, the gains applied to the past values or the phases of the past values in accordance with the resonance mode occurring in the HDA 10 or the like to adjust the suppression amount Uls. For example, the system controller 130 may correct the phases of the past values corresponding to a phase shift having occurred in a system preceding an input to the filter FT or a system succeeding an output from the filter FT. The system controller 130 may also correct a phase shift with respect to the phase of a loop shaping frequency identified in the system preceding the input to the filter FT or the system succeeding the output from the filter FT.

FIG. 19 and FIG. 20 are diagrams illustrating an example of a state of vibration of the heads HD, the arms AM, and the VCM 14 in a case where the resonance mode occurs in the HDA 10 , according to the second embodiment. FIG. 19 and FIG. 20 illustrate the heads HD, the arms AM, and the VCM 14 in a case where an X-Z plane is viewed from a tip of an arrow for the second direction Y in FIG. 2 . If the resonance mode illustrated in FIG. 19 and FIG. 20 occurs in the HDA 10 , the heads HD, the arms AM, and the VCM 14 may be vibrated in a coupled manner. A direction depicted by the arrow for the first direction X is hereinafter referred to as the left side, and the direction opposite to the left side is hereinafter referred to as the right side. The heads HD, the arms AM, and the VCM 14 illustrated in FIG. 19 are inclined to the left side with respect to the axis AX. The heads HD, the arms AM, and the VCM 14 illustrated in FIG. 20 are inclined to the right side with respect to the axis AX. In FIG. 19 and FIG. 20 , the head HD further includes a head HD 4 , a head HD 5 , a head HD 6 , and a head HD 7 . Furthermore, in FIG. 19 and FIG. 20 , the arm AM further includes an arm AM 4 , an arm AM 5 , an arm AM 5 , an arm AM 6 , and an arm AM 7 .

In the example illustrated in FIG. 19 , the heads HD 0 to HD 3 are displaced toward the left side with respect to the axis AX. The heads HD 4 to HD 7 are displaced toward the right side with respect to the axis AX. The heads HD 0 to HD 7 are arranged in tandem in such a manner as to incline upward to the left with respect to the axis AX.

In the example illustrated in FIG. 20 , the heads HD 0 to HD 3 are displaced toward the right side with respect to the axis AX. The heads HD 4 to HD 7 are displaced toward the left side with respect to the axis AX. The heads HD 0 to HD 7 are arranged in tandem in such a manner as to incline upward to the right with respect to the axis AX.

FIG. 21 is a diagram illustrating an example of amplitudes corresponding to the heads HD and the arms AM in a case where the HDA 10 is vibrated as illustrated in FIG. 19 and FIG. 20 . In FIG. 21 , the ordinate axis indicates the amplitude, and the abscissa axis indicates the heads HD and the arms AM corresponding to the respective amplitudes. In FIG. 21 , the amplitudes corresponding to the heads HD and the arms AM are each normalized using a particular value. Thus, in FIG. 21 , the amplitudes corresponding to the heads HD and the arms AM fluctuate between a particular value with the positive polarity, for example, 1, and a particular value with the negative polarity, for example, −1. In FIG. 21 , for the amplitude, the maximum value with the positive polarity is 1, and the maximum value with the negative polarity is −1.

In the example illustrated in FIG. 21 , amplitudes AP 210 to AP 217 for the heads HD 0 to HD 7 and the arms AM 0 to AM 7 vary at a constant gradient from the maximum value with the positive polarity (1) to the maximum value with the negative polarity (−1).

If a resonance mode occurs which varies the amplitudes of the heads HD and the arms AM as illustrated in FIG. 21 , the system controller 130 executes the disturbance suppression process, for example, the loop shaping process. For example, if the head HD 0 is changed to the head HD 1 , the system controller 130 inputs, to the filter FT, the past values multiplied by the ratio of the amplitude AP 210 of the head HD 0 to the amplitude AP 211 of the head HD 1 (AP 211 /AP 210 ). If the head HD 0 is changed to the head HD 6 , the system controller 130 inputs, to the filter FT, the past values multiplied by the ratio of the amplitude AP 210 of the head HD 0 to the amplitude AP 216 of the head HD 6 (AP 216 /AP 210 ). The system controller 130 generates the suppression amount Uls based on the currently input estimated position error Ep, the currently input model position error Epm, the past values, and the like.

FIG. 22 and FIG. 23 are diagrams illustrating an example of the state of vibration of the heads HD, the arms AM, and the VCM 14 in a case where the resonance mode according to the second embodiment occurs in the HDA 10 . FIG. 22 and FIG. 23 illustrate the heads HD, the arms AM, and the VCM 14 in a case where the X-Z plane is viewed from the tip of the arrow for the second direction Y in FIG. 2 .

In the example illustrated in FIG. 22 , the head HD 0 and the arm AM 0 are inclined to the right side with respect to the axis AX. The heads HD 1 to HD 6 and the arms AM 1 to AM 6 are not substantially inclined with respect to the axis AX. The head HD 7 and the arm AM 7 are inclined to the left side with respect to the axis AX.

In the example illustrated in FIG. 23 , the head HD 0 and the arm AM 0 are inclined to the left side with respect to the axis AX. The heads HD 1 to HD 6 and the arms AM 1 to AM 6 are not substantially inclined with respect to the axis AX. The head HD 7 and the arm AM 7 are inclined to the right side with respect to the axis AX.

FIG. 24 is a diagram illustrating an example of amplitudes corresponding to the heads HD and the arms AM in a case where the HDA 10 is vibrated as illustrated in FIG. 22 and FIG. 23 . In FIG. 24 , the ordinate axis indicates the amplitude, and the abscissa axis indicates the heads HD and the arms AM corresponding to the respective amplitudes. In FIG. 24 , the amplitudes corresponding to the heads HD and the arms AM are each normalized using a particular value. Thus, in FIG. 24 , the amplitudes corresponding to the heads HD and the arms AM fluctuate between a particular value with the positive polarity, for example, 1, and a particular value with the negative polarity, for example, −1. In FIG. 24 , for the amplitude, the maximum value with the positive polarity is 1, and the maximum value with the negative polarity is −1.

In the example illustrated in FIG. 24 , an amplitude AP 240 for the head HD 0 and the arm AM 0 is the maximum value with the positive polarity (1). The amplitudes AP 241 to AP 246 for the heads HD 1 to HD 6 and the arms AM 1 to AM 6 are 0. An amplitude AP 247 for the head HD 7 and the arm AM 7 is the maximum value with the positive polarity (1).

If a resonance mode occurs which varies the amplitudes of the heads HD and the arms AM as illustrated in FIG. 24 , the system controller 130 executes the disturbance suppression process, for example, the loop shaping process. For example, if the head HD 0 is changed to the head HD 1 , the system controller 130 inputs, to the filter FT, the past values multiplied by the ratio of the amplitude AP 240 of the head HD 0 to the amplitude AP 241 of the head HD 1 (AP 241 /AP 240 ). If the head HD 0 is changed to the head HD 7 , the system controller 130 inputs, to the filter FT, the past values multiplied by the ratio of the amplitude AP 240 of the head HD 0 to the amplitude AP 247 of the head HD 7 (AP 247 /AP 240 ). The system controller 130 generates the suppression amount Uls based on the currently input estimated position error Ep, the currently input model position error Epm, the past values, and the like.

According to the second embodiment, if a head change is performed with a resonance mode other than the synchronous resonance mode occurring, the magnetic disk device 1 can suppress the adverse effects of vibration resulting from the resonance mode other than the synchronous resonance mode during seeking by the next head HD. Therefore, the magnetic disk device 1 is capable of improving the accuracy of the servo control.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.