Patent Publication Number: US-2023142495-A1

Title: Disk device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-181249, filed on Nov. 5, 2021; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a disk device. 
     BACKGROUND 
     In a disk device having a head and a disk, the head is moved with respect to a surface of the disk, and a write operation to the disk is performed by the head. In the disk device, it is desirable that the write operation is appropriately performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating a configuration of a disk device according to a first embodiment; 
         FIG.  2    is a plan view illustrating a configuration of a disk in the first embodiment; 
         FIG.  3    is a plan view illustrating positioning of a head in the first embodiment; 
         FIGS.  4 A and  4 B  are diagrams illustrating a change in correlation between an actual position and a predicted position according to vibration in the first embodiment; 
         FIGS.  5 A and  5 B  are diagrams illustrating a data structure of coefficient information in the first embodiment; 
         FIG.  6    is a flowchart illustrating an operation in tracking of the disk device according to the first embodiment; 
         FIG.  7    is a flowchart illustrating predicted position coefficient update processing in the first embodiment; 
         FIG.  8    is a diagram illustrating a configuration of a disk device according to a second embodiment; 
         FIG.  9    is a diagram illustrating transmission characteristics of vibration between actuators in the second embodiment; 
         FIGS.  10 A to  10 D  are diagrams illustrating changes in a seek current and a position error signal according to vibration in the second embodiment; 
         FIG.  11    is a diagram illustrating a difference in transmission characteristics of vibration for each head in the second embodiment; 
         FIGS.  12 A to  12 D  are diagrams illustrating changes in the seek current and the position error signal according to vibration in the second embodiment; 
         FIGS.  13 A and  13 B  are diagrams illustrating a data structure of coefficient information in the second embodiment; 
         FIG.  14    is a flowchart illustrating an operation in seeking of the disk device according to the second embodiment; 
         FIG.  15    is a flowchart illustrating an operation in tracking of the disk device according to the second embodiment; and 
         FIG.  16    is a flowchart illustrating predicted position coefficient update processing in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, there is provided a disk device including a first disk, a first head, a first actuator and a controller. The first actuator moves the first head with respect to a first surface of the first disk. The controller controls positioning of the first head via the first actuator and controls a write operation to the first disk by the first head. The controller acquires information regarding a state of a vibration source, changes a value of a coefficient for estimating a predicted position of the first head according to the information regarding the state of the vibration source, estimates a predicted position of the first head with the value of the coefficient changed, performs a write operation by the first head in a case where the predicted position estimated is equal to or less than a threshold, and prohibits the write operation by the first head in a case where the predicted position estimated exceeds the threshold. 
     Exemplary embodiments of a disk device will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the following embodiments. 
     First Embodiment 
     In the disk device according to a first embodiment, a write prohibition determination based on the predicted position of the head is performed, and a device for improving the accuracy of the write prohibition determination is provided. 
     For example, the disk device  100  is configured as illustrated in  FIG.  1   .  FIG.  1    is a diagram illustrating a configuration of a disk device  100 , in which a part of the configuration of the disk device  100  is illustrated in a cross-sectional view and the other part is illustrated in a block diagram. Hereinafter, a direction along the rotation axis of the disk DK 1  is referred to as a Z direction, and two directions orthogonal to each other in a plane perpendicular to the Z direction are referred to as an X direction and a Y direction. 
     The disk device  100  includes a housing  1 , a disk DK 1 , a head H 0 , a head H 1 , an actuator AC 1 , a spindle motor  3 , a spindle  10 , rotational vibration (RV) sensors  11 A and  11 B, a shock sensor  12 , a write prohibition detector  13 , and a controller  5 . 
     The housing  1  includes a base  1   a  extending in a flat plate shape in the X and Y directions and a cover  1   b  which is not illustrated. The disk DK 1 , the head H 0 , the actuator AC 1 , the spindle motor (SPM)  3 , the spindle  10 , the RV sensor  11 , the shock sensor  12 , and the write prohibition detector  13  are accommodated in a space where the cover  1   b  closes the base  1   a  from a +Z side. 
     As illustrated in  FIG.  2   , the disk DK 1  is a substantially disk-shaped medium on which information is to be recorded.  FIG.  2    is a plan view illustrating a configuration of the disk DK 1 . The disk DK 1  is supported by the base of the housing  1  via the spindle  10  so as to be rotatable about the Z axis. The disk DK 1  may be a magnetic disk or a magneto-optical disk. Hereinafter, a case where the disk DK 1  is a magnetic disk will be mainly exemplified. The disk DK 1  has a recording surface M 0  on the +Z side and a recording surface M 1  on a −Z side. In the disk DK 1 , plural tracks TR concentric in a radial direction are defined by servo information written in advance in a radial servo region SR on each of the recording surfaces M 0  and M 1 . An area between servo regions SR on each of the recording surfaces M 0  and M 1  of the disk DK 1  is a data region DR in which data can be written. Each track TR includes one or more sets of the servo region SR and the data region DR in a circumferential direction. 
     The head H 0  illustrated in  FIG.  1    is held by the actuator AC 1  and disposed so as to face the recording surface M 0  of the disk DK 1 . The head H 1  is held by the actuator AC 1  and is disposed so as to face the recording surface M 1  of the disk DK 1 . Each of the heads H 0  and H 1  includes a write head and a read head. The actuator AC 1  moves the heads H 0  and H 1  with respect to the recording surfaces M 0  and M 1  at the time of seek or the like, and positions the heads H 0  and H 1  to one of the plural tracks TR. 
     The actuator AC 1  includes a voice coil motor (VCM)  4  and actuator arms AM 0  and AM 1 . The head H 0  is provided at a position on the disk DK 1  side (recording surface M 0  side) at a distal end of the actuator arm AM 0 . The head H 1  is provided at a position on the disk DK 1  side (recording surface M 1  side) at a distal end of the actuator arm AM 1 . 
     Note that the actuator AC 1  may further include microactuators MA 0  and MA 1 . In this case, the microactuators MA 0  and MA 1  are provided at the distal ends of the actuator arms AM 0  and AM 1 . The head H 0  is provided at a position on the disk DK 1  side (recording surface M 0  side) at a distal end of the microactuator MA 0 . The head H 1  is provided at a position on the disk DK 1  side (recording surface M 1  side) at a distal end of the microactuator MA 1 . 
     At the time of seek or the like, the actuator AC 1  drives the actuator arms AM 0  and AM 1  with a shaft AX 1  as a rotation center by the voice coil motor  4  as illustrated in  FIG.  3   .  FIG.  3    is a view illustrating positioning of the heads H 0  and H 1 . In a case where the actuator arms AM 0  and AM 1  are configured to rotate simultaneously, the actuator AC 1  may move and position the heads H 0  and H 1  simultaneously. 
     For example, the actuator AC 1  causes the heads H 0  and H 1  to seek in a horizontal direction on a trajectory T via the actuator arms AM 0  and AM 1 , and positions the heads H 0  or H 1  to the target track TR. The actuator AC 1  causes the heads H 0  or H 1  to track on the target track TR. 
     The actuator arms AM 0  and AM 1  illustrated in  FIG.  1    can keep flying heights of the heads H 0  and H 1  on the +Z side and the −Z side of the recording surfaces M 0  and M 1  of the disk DK 1  constant by applying, to the heads H 0  and H 1 , a pressing force against the flying force of the heads H 0  and H 1  due to airflow when the disk DK 1  rotates. The spindle motor  3  rotates the magnetic disk DK 1  around the spindle  10 . The voice coil motor  4  and the spindle motor  3  are fixed to the base  1   a  of the housing  1 . 
     Each of the RV sensors  11 A and  11 B and the shock sensor  12  detects vibration of a vibration source. The vibration source is a source of vibration that can be exerted on the actuator AC 1 . 
     As illustrated in  FIG.  3   , the RV sensors  11 A and  11 B are fixed to the base  1   a  of the housing  1  at positions with the disk DK 1  interposed therebetween in an XY plane direction. Each of the RV sensors  11 A and  11 B can detect the amount of vibration in the X direction and the Y direction. The difference between a detection value of the RV sensor  11 A and a detection value of the RV sensor  11 B is amplified by a differential amplifier (not illustrated), and thus the amount of vibration of the disk DK 1  in a substantially circumferential direction can be detected. The RV sensors  11 A and  11 B supply detection results of the amount of vibration to the controller  5 . 
     The shock sensor  12  can detect the amount of vibration in each of the X, Y, and Z directions. The amount of vibration detected by the shock sensor  12  is a displacement amount, velocity, acceleration, or any other physical quantity. The shock sensor  12  is fixed to the base  1   a  of the housing  1 , and can detect the amount of vibration in the X direction, the Y direction, and the Z direction of the housing  1 . 
     The write prohibition detector  13  receives a detection result from the shock sensor  12 . The write prohibition detector  13  detects write prohibition when the amount of vibration detected by the shock sensor  12  exceeds a predetermined threshold. The write prohibition detector  13  does not detect the write prohibition when the amount of vibration detected by the shock sensor  12  is within a predetermined threshold. 
     The controller  5  is communicably connected to a host system HS, and upon receiving a command from the host system HS, the controller  5  can perform control according to the command. 
     The controller  5  includes a head amplifier  6 , a driver  7 , a read/write (R/W) channel  8 , a hard disk control unit (HDC)  9 , a volatile memory  14 , a buffer memory  15 , and a nonvolatile memory  16 . 
     The controller  5  performs overall control of the disk device  100  according to firmware stored in advance in the nonvolatile memory  16  or the disk DK 1 . The firmware is initial firmware and control firmware used for normal operation. The initial firmware executed first at the time of activation is stored in, for example, the nonvolatile memory  16 , and the control firmware used for the normal operation is recorded in the disk DK 1 . Under the control according to the initial firmware, data is temporarily read from the disk DK 1  to the buffer memory  15  and then stored in the volatile memory  14 . 
     The head amplifier  6  selects the heads H 0  and H 1  and amplifies a signal at the time of writing or detects a signal at the time of reading. The head amplifier  6  includes a write current control unit  6 A, a read signal detection unit  6 B, and a head selection unit  6 C. The head selection unit  6 C selects a head H to be used from the heads H 0  and H 1 . The controller  5  controls and positions the position of the head H with respect to the disk DK 1  on the basis of the servo information read by the selected head H. The write current control unit  6 A controls a write current flowing through the write head in the head H in a state where the head H is positioned. The read signal detection unit  6 B detects a signal read by the read head in the head H in a state where the head H is positioned. The head amplifier  6  can be implemented as an integrated circuit (IC). 
     The driver  7  drives the voice coil motor  4  and the spindle motor  3 , and captures rotational vibration (RV) signals from the RV sensors  11 A and  11 B. The driver  7  includes a spindle motor (SPM) control unit  7 A, a voice coil motor (VCM) control unit  7 B, and an RV signal capturing unit  7 D. The spindle motor control unit  7 A controls rotation of the spindle motor  3 . The voice coil motor control unit  7 B controls driving of the voice coil motor  4 . The RV signal capturing unit  7 D captures rotational vibration signals (RV signals) from the RV sensors  11 A and  11 B. 
     Note that, in a case where the actuator AC 1  further includes the microactuators MA 0  and MA 1 , the driver  7  further includes a microactuator (MA) control unit  7 C. The microactuator (MA) control unit  7 C controls driving of the microactuators MA 0  and MA 1 . Thus, the position of the head H can be finely adjusted. 
     The read/write channel  8  exchanges data between the head amplifier  6  and the hard disk control unit  9 . Note that the data includes read data, write data, and the servo information. The read/write channel  8  includes a write prohibition unit  8 A. The write prohibition unit  8 A includes a sensor write prohibition unit  8 A 1  and an HDC write prohibition unit  8 A 2 . 
     The sensor write prohibition unit  8 A 1  receives a detection result of the write prohibition detector  13 . When the write prohibition has been detected, the sensor write prohibition unit  8 A 1  supplies a write prohibition instruction to the head amplifier  6 . When the write prohibition has not been detected, the sensor write prohibition unit  8 A 1  supplies a write permission instruction to the head amplifier  6 . 
     The HDC write prohibition unit  8 A 2  receives a determination result of the write prohibition determination from the hard disk control unit  9 . When the determination result is write prohibition, the HDC write prohibition unit  8 A 2  supplies the write prohibition instruction to the head amplifier  6 . When the determination result is write permission, the HDC write prohibition unit  8 A 2  supplies the write permission instruction to the head amplifier  6 . 
     Upon receiving the write prohibition instruction from at least one of the sensor write prohibition unit  8 A 1  or the HDC write prohibition unit  8 A 2 , the head amplifier  6  prevents the write operation to the disk DK 1  by the head H from being performed. That is, the write current control unit  6 A prevents the write current from flowing through the write head in the head H. 
     Upon receiving the write permission instruction from both the sensor write prohibition unit  8 A 1  and the HDC write prohibition unit  8 A 2 , the head amplifier  6  causes the head H to perform the write operation to the disk DK 1 . That is, the write current control unit  6 A controls the write current flowing through the write head in the head H in a state where the head H is positioned. 
     The hard disk control unit  9  performs write control and read control on the basis of a write command and a read command from the outside of the disk device  100  (for example, host system HS), and exchanges data between the outside and the read/write channel  8 . The configuration including the driver  7 , the read/write channel  8 , and the hard disk control unit  9  can be implemented as a system-on-chip. 
     The hard disk control unit  9  includes a command control unit  9 A and a servo control unit  6 B. The command control unit  9 A controls an operation according to a command received from the host system HS. The command control unit  9 A includes a command selection unit  9 A 1 . When the hard disk control unit  9  receives a command from the host system HS, the command selection unit  9 A 1  recognizes the received command and selects a control operation according to the recognized command. The command selection unit  9 A 1  specifies an address or the like included in the command. 
     In a case where the command is a write command, the command selection unit  9 A 1  selects write control according to the write command. The command selection unit  9 A 1  specifies each of a write address and write data included in the write command. 
     The servo control unit  9 B controls the position of the head H according to the control operation selected by the command selection unit  9 A 1 . A tracking control unit  9 B 1 , a seek control unit  9 B 2 , and a write operation determination unit  9 B 3  are included. 
     The seek control unit  9 B 2  controls the seek of the head H to the target track TR on the disk DK 1  according to the address (for example, the write address) included in the command. The seek control unit  9 B 2  controls the actuator AC 1  via the read/write channel  8  and the head amplifier  6 , causes the head H to seek in the horizontal direction on the trajectory T via the actuator arm AM, and positions the head H to the target track TR. The target track TR is a track TR corresponding to the address (for example, the write address) included in the command. 
     The tracking control unit  9 B 1  controls tracking of the head H on the target track TR of the disk DK 1 . The tracking control unit  9 B 1  controls the actuator AC 1  via the read/write channel  8  and the head amplifier  6 , and causes the head H to track on the target track TR via the actuator arm AM. 
     Here, the hard disk control unit  9  has a function of performing write prohibition determination in a case where the command is a write command. In a state where the head H is positioned and caused to track on the target track according to the write address, the write operation determination unit  9 B 3  performs the write prohibition determination. There are several types of write prohibition determination, and the types include a write prohibition determination based on a current position and a write prohibition determination based on a predicted position. The write operation determination unit  9 B 3  includes a position operation determination unit  9 B 31  and a predicted position operation determination unit  9 B 32 . The position operation determination unit  9 B 31  performs the write prohibition determination based on the current position, and the predicted position operation determination unit  9 B 32  performs the write prohibition determination based on the predicted position. 
     The servo control unit  9 B demodulates a position error signal according to the servo information read from the servo region via the head H. The position error signal indicates a relative position of the head H from the center of the track TR. The servo control unit  9 B obtains a current actual position of the head H and a velocity component immediately before reaching the current actual position according to the position error signal. The servo control unit  9 B may obtain the current actual position of the head H as an absolute value of a current displacement from the center of the track TR of the head H. The servo control unit  9 B estimates a future predicted position according to the current actual position of the head H and the velocity component immediately before reaching the current actual position. The servo control unit  9 B may obtain the future predicted position of the head H as an absolute value of a future displacement from the center of the track TR of the head H. 
     The predicted position operation determination unit  9 B 32  performs the write prohibition determination in accordance with the predicted position. The predicted position operation determination unit  9 B 32  determines that writing is possible when the estimated predicted position is equal to or less than a threshold, and determines that writing is not possible when the estimated predicted position has exceeded the threshold. The servo control unit  9 B performs the write operation on the disk DK 1  by the head H if the predicted position operation determination unit  9 B 32  determines that writing is possible, and does not perform the write operation on the disk DK 1  by the head H if the predicted position operation determination unit  9 B 32  determines that writing is not possible. In order to prevent shifted writing in which data is written out of the target track TR, it is desirable that an estimated value of the predicted position used for the write prohibition determination is accurate. 
     For example, it is assumed that the servo control unit  9 B causes the head H to track on the target track TR. The actual position measured with the servo information read by the head H is represented by p, and the predicted position predicted by the servo control unit  9 B is represented by p{circumflex over ( )}. Each of the actual position p and the predicted position p{circumflex over ( )} indicates an absolute value of a position error from a radial center position of the target track TR. The servo control unit  9 B acquires (samples) servo information at each predetermined sample interval, and obtains the current actual position of the head H and the velocity component immediately before reaching the current actual position. The simplest implementation of the predicted position p{circumflex over ( )} is by linear interpolation and is represented by the following Mathematical Expression 1. 
         p {circumflex over ( )}( k+ 1)= p ( k )+( p ( k )− p ( k− 1))=2 p ( k )− p ( k− 1)  Mathematical Expression 1
 
     In Mathematical Expression 1, k represents a current sample timing, k−1 represents a past sample timing before one sample interval, and k+1 represents a future sample timing after one sample interval. As represented in Mathematical Expression 1, a predicted position p{circumflex over ( )}(k+1) at one sample interval future is obtained by performing linear interpolation for the current position p(k) with a displacement (p(k)−p(k−1)) from the past. 
     The purpose of performing the write prohibition determination by the predicted position is to reduce the possibility that the head H protrudes from the target track TR (overrun) and erodes and rewrites the data of the adjacent track TR when positioning of the head H is controlled to the target track TR. 
     The position error signal indicating the position of the head H can be obtained only in discrete time (sample interval), and there is a time delay between the position demodulation processing and the write prohibition determination. Thus, in a case where the write prohibition determination is made based on the current actual position, even if it is determined that writing is possible with a certain threshold, there is a possibility that writing is actually performed beyond the threshold. In order not to delete the data of the adjacent track, it is necessary to suppress the protrusion amount to a certain value or less, and thus, not only the write prohibition determination based on the current actual position but also the write prohibition determination based on the future predicted position are used. 
     Here, (p(k)−p(k−1)) represents a velocity component due to displacement from one sample interval before to the present, but velocity estimation due to displacement has a large error. Thus, in the write prohibition determination based on the predicted position of Mathematical Expression 1, a different threshold T h2  is used with respect to a threshold T h1  used in the write prohibition determination based on the current actual position. The determination condition at this time is represented by the following Mathematical Expression 2. 
         p {circumflex over ( )}( k+ 1)=2 p ( k )− p ( k− 1)&gt; T   h1   Mathematical Expression 2
 
     In Mathematical Expression 2, if T h2 =a 1 ×T h1 , Mathematical Expression 2 can be rewritten into the following Mathematical Expression 3. 
         p {circumflex over ( )}( k+ 1)/ a   1 =(2/ a   1 )× p ( k )+(−1/ a   1 )× p ( k− 1)&gt; T   h1   Mathematical Expression 3
 
     When the generalized coefficients a and b are introduced in Mathematical Expression 3, Mathematical Expression 3 can be rewritten into the following Mathematical Expression 4. 
         p {circumflex over ( )}( k+ 1)/ a   1   =a×p ( k )+ b×p ( k− 1)&gt; T   h1    Mathematical Expression 4
 
     The coefficients a and b in Mathematical Expression 4 can be made appropriate (for example, optimized) on the basis of time history data of the actual position and the like. In a case where the coefficients a and b are made appropriate for a certain vibration state, it is assumed that the predicted position estimated by the coefficients a and b and the actual position have a good correlation. In this case, if the same coefficients a and b are used in different vibration states, the prediction accuracy may deteriorate. This is considered to be because appropriate values (for example, optimum values) of the coefficients a and b change depending on the frequency component of vibration. 
     For example, it is assumed that the actuator AC 1  receives vibration including a peak frequency component at the frequency F (for example, 5 kHz). At this time, the position error signal indicates a frequency spectrum SP indicated by a one-dot chain line in  FIG.  4 A .  FIGS.  4 A and  4 B  are diagrams illustrating changes in correlation between the actual position and the predicted position according to vibration. The frequency spectrum SP has a peak at the frequency F. In this state, when the servo control unit  9 B estimates the predicted position by making the coefficients a and b appropriate, the predicted position estimated by the coefficients a and b and the actual position are distributed as DS indicated by a one-dot chain line in  FIG.  4 B . The distribution DS is generally a distribution along an ideal correlation straight line IL indicated by a dotted line in  FIG.  4 B , and indicates that the predicted position estimated by the coefficients a and b has a good correlation with the actual positions. 
     At this time, it is assumed that the vibration received by the actuator AC 1  is changed to vibration including a peak frequency component in the frequency F′ (for example, 10 kHz). At this time, the position error signal indicates a frequency spectrum SP′ indicated by a two-dot chain line in  FIG.  4 A . The frequency spectrum SP′ has a peak at the frequency F′. In this state, when the servo control unit  9 B estimates the predicted position using the same coefficients a and b as described above, the predicted position estimated by the coefficients a and b and the actual position are distributed as DS′ indicated by a two-dot chain line in  FIG.  4 B . The distribution DS′ is a distribution deviating from the ideal correlation straight line IL indicated by a dotted line in  FIG.  4 B , and indicates that the correlation between the predicted position estimated by the coefficients a and b and the actual position has deteriorated. 
     On the other hand, the hard disk control unit  9  further includes a predicted position coefficient updating unit  9 B 4 . The predicted position coefficient updating unit  9 B 4  acquires information regarding the state of the vibration source. The predicted position coefficient updating unit  9 B 4  may acquire the detection results of the RV sensors  11 A and  11 B as information regarding the state of the vibration source, or may acquire the position error signal generated by the servo control unit  9 B as information regarding the state of the vibration source. The predicted position coefficient updating unit  9 B 4  changes the values of the coefficients a and b for estimating the predicted position of the head H according to the information regarding the state of the vibration source. The predicted position coefficient updating unit  9 B 4  may estimate the frequency of vibration of the vibration source according to the detection results of the RV sensors  11 A and  11 B, or may estimate the frequency of vibration of the vibration source according to the position error signal. The predicted position coefficient updating unit  9 B 4  may change the values of the coefficients a and b according to the estimated frequency. 
     In addition, in a case where the actuator AC 1  receives vibration from a certain vibration source, the plural heads H 0  and H 1  moved by the actuator AC 1  are different from each other in how the vibration is transmitted. Even if the frequency of vibration is the same, an appropriate value (for example, an optimum value) of the coefficient may be different for each of the heads H 0  and H 1 . Thus, the predicted position coefficient updating unit  9 B 4  may change the values of the coefficients a and b for each of the heads H 0  and H 1  according to the estimated frequency. 
     For example, coefficient information as illustrated in  FIGS.  5 A and  5 B  may be stored in the nonvolatile memory  16  or the disk DK 1 .  FIGS.  5 A and  5 B  are diagrams illustrating a data structure of coefficient information.  FIG.  5 A  illustrates a frequency level definition table as part of the coefficient information, and  FIG.  5 B  illustrates a predicted position coefficient table as another part of the coefficient information. In  FIG.  5 B , the coefficients are indicated by a(head identifier, frequency level) and b(head identifier, frequency level). 
     In the frequency level definition table illustrated in  FIG.  5 A , a frequency range and a frequency level are associated for plural frequency ranges. For example, a range of frequencies F 0  to F 1  is defined as a frequency level “0”. A range of frequencies F 1  to F 2  is defined as a frequency level “1”. A range of frequencies FM to F(M+1) is defined as a frequency level “M”. M is an arbitrary integer of 2 or more. 
     In the predicted position coefficient table illustrated in  FIG.  5 B , a head identifier (for example, a head number), a frequency level, and a predicted position coefficient are associated with each head for plural frequency levels. For the head H 0  of the head identifier “0”, coefficients a(0, 0) and b(0, 0) correspond to the frequency level “0”, and coefficients a(0, M) and b(0, M) correspond to the frequency level “M”. For the head H 1  of the head identifier “1”, coefficients a(1, 0) and b(1, 0) correspond to the frequency level “0”, and coefficients a(1, M) and b(1, M) correspond to the frequency level “M”. 
     The predicted position coefficient updating unit  9 B 4  can update the values of the coefficients a and b for each of the heads H 0  and H 1  by using the frequency level definition table illustrated in  FIG.  5 A  and the predicted position coefficient table illustrated in  FIG.  5 B  according to the estimated frequency. 
     Note that the coefficient information for changing the values of the coefficients a and b may be mounted on the disk device  100  in the form of a mathematical expression instead of the form of the table illustrated in  FIGS.  5 A and  5 B . For example, information of expressions such as the following Mathematical Expressions 5 and 6 may be stored in the nonvolatile memory  16  or the disk DK 1  and referred to by the predicted position coefficient updating unit  9 B 4 . f a  includes an arbitrary mathematical expression in which the coefficient a is represented by a function of a peak frequency of vibration as a variable. f b  includes an arbitrary mathematical expression in which the coefficient b is represented by a function of a peak frequency of vibration as a variable. 
         a (head identifier,frequency level)= f   a (peak frequency of vibration)  Mathematical Expression 5
 
         b (head identifier,frequency level)= f   b (peak frequency of vibration)  Mathematical Expression 6
 
     Next, an operation of the disk device  100  will be described with reference to  FIG.  6   .  FIG.  6    is a flowchart illustrating an operation in tracking of the disk device  100 . The disk device  100  can perform the operation illustrated in  FIG.  6    as interrupt processing for each sample timing in a state where the head H is made to track on the target track TR. 
     The controller  5  calculates the actual position of the head H by servo demodulation in a state where the head H is made to track on the target track TR (S 1 ). The controller  5  reads the servo information from the servo region SR via the read head of the head H. The controller  5  demodulates the position error signal according to the servo information. The position error signal indicates the relative position of the head H from the center of the track TR. The controller  5  obtains the current actual position of the head H according to the position error signal. 
     The controller  5  determines whether or not the actual position p(k) of the head H has exceeded the threshold T h1  (S 2 ). If the actual position p(k) of the head H has exceeded the threshold T h1  (YES in S 2 ), the controller  5  determines that write is prohibited (S 11 ) and does not perform the write operation. 
     If the actual position p(k) of the head H is equal to or less than the threshold T h1  (NO in S 2 ), the controller  5  determines that there is a possibility of permission for writing and acquires detection results of the sensors such as the RV sensors  11 A and  11 B (S 3 ). The controller  5  estimates the vibration state of the vibration source according to the detection results of the sensors (S 4 ). The controller  5  may estimate an amplitude and a direction of vibration as the state of the vibration source. The controller  5  determines a vibration control instruction value so as to suppress vibration according to the estimated vibration state (S 5 ), and performs control according to the vibration control instruction value (S 6 ). As the control, the controller  5  may perform vibration control of vibrating the actuator AC 1  so as to cancel the influence of vibration. 
     The controller  5  performs a predicted position coefficient update processing (S 7 ). The controller  5  may perform processes of S 21  to S 23  illustrated in  FIG.  7    as the predicted position coefficient update processing.  FIG.  7    is a flowchart illustrating the predicted position coefficient update processing. 
     The controller  5  generates a position error signal by the servo demodulation in a state where the control of S 6  is performed (S 21 ). The controller  5  estimates a disturbance state of the actuator AC 1  according to the position error signal (S 22 ). The disturbance state includes a state of vibration due to disturbance (for example, vibration by a fan, and the like) that cannot be suppressed by control such as vibration control. The controller  5  may estimate the frequency of vibration due to disturbance as the disturbance state. 
     The controller  5  updates the values of the coefficients a and b for obtaining the predicted position according to the estimated disturbance state (S 23 ). The controller  5  may update the values of the coefficients a and b with reference to coefficient information as illustrated in  FIGS.  5 A and  5 B  according to the frequency of vibration due to disturbance. 
     For example, when the frequency F (see  FIG.  4 A ) of vibration due to disturbance is within the range of frequencies F 0  to F 1 , the predicted position coefficient updating unit  9 B 4  refers to the frequency level definition table illustrated in  FIG.  5 A  and specifies the frequency level as “0”. The predicted position coefficient updating unit  9 B 4  refers to the predicted position coefficient table illustrated in  FIG.  5 B , updates the coefficients of the head H 0  to a(0, 0) and b(0, 0) corresponding to the frequency level “0”, and updates the coefficients of the head H 1  to a(1, 0) and b(1, 0) corresponding to the frequency level “0”. 
     Alternatively, when the frequency F′ (see  FIG.  4 A ) of the vibration due to the disturbance is within the range of the frequencies F 1  to F 2 , the predicted position coefficient updating unit  9 B 4  refers to the frequency level definition table illustrated in  FIG.  5 A  and specifies the frequency level as “1”. The predicted position coefficient updating unit  9 B 4  refers to the predicted position coefficient table illustrated in  FIG.  5 B , updates the coefficients of the head H 0  to a(0, 1) and b(0, 1) corresponding to the frequency level “1”, and updates the coefficients of the head H 1  to a(1, 1) and b(1, 1) corresponding to the frequency level “1”. 
     When the values of the coefficients a and b are updated, as illustrated in  FIG.  6   , the controller  5  estimates the predicted position of the head H using the coefficients a and b after the update (S 8 ). The controller  5  may estimate a parameter p{circumflex over ( )}(k+1)/a 1  corresponding to the predicted position of the head H by Mathematical Expression 4 using the coefficients a and b after the update. 
     For example, in a case where the write operation is to be performed in the head H 0  according to the write address included in the write command, if the coefficients of the head H 0  are updated to a(0, 0) and b(0, 0) in S 6 , then a(0, 0) and b(0, 0) may be substituted into Mathematical Expression 4 to estimate the parameter p{circumflex over ( )}(k+1)/a 1 . 
     The controller  5  determines whether or not the predicted position p{circumflex over ( )}(k+1) of the head H has exceeded the threshold T h2  (S 9 ). The controller  5  may determine whether or not the inequality of Mathematical Expression 4 is satisfied using the coefficients a and b after the update. The controller  5  can determine that the predicted position p{circumflex over ( )}(k+1) of the head H has exceeded the threshold T h2  if the inequality of Mathematical Expression 4 is satisfied using the coefficients a and b after the update. The controller  5  can determine that the predicted position p{circumflex over ( )}(k+1) of the head H is equal to or less than the threshold T h2  if the inequality of Mathematical Expression 4 is not satisfied using the coefficients a and b after the update. 
     If the predicted position p{circumflex over ( )}(k+1) of the head H has exceeded the threshold T h2  (YES in S 9 ), the controller  5  determines that write is prohibited (S 11 ) and does not perform the write operation by the head H. 
     When the predicted position p{circumflex over ( )}(k+1) of the head H is equal to or less than the threshold T h z (NO in S 9 ), the controller  5  determines that the write is permitted (S 10 ) and performs the write operation by the head H. The controller  5  applies a write current to the write head of the head H, and writes write data in the data region DR of the target track TR. 
     As described above, in the first embodiment, in the disk device  100 , the controller  5  acquires the information regarding the state of the vibration source, changes the values of the coefficients for estimating the predicted position of the head H according to the information regarding the state of the vibration source, and estimates the predicted position of the head H with the changed values of the coefficients. In this manner, the estimation accuracy of the predicted position can be improved, and thus the accuracy of the write prohibition determination based on the predicted position can be improved. Consequently, it is possible to secure a period during which the head H can properly perform the write operation in the target track TR while preventing shifted writing in which the head H protrudes from the target track TR to the adjacent track TR and overwrites thereon. That is, in a case where vibration is generated, both improvement in reliability and improvement in performance of the write operation can be achieved, and the write operation can be appropriately performed. 
     Note that in the operation illustrated in  FIG.  6   , the processing of S 3  may be omitted. In this case, the controller  5  may estimate the vibration state in S 4  using the position error signal generated in S 1  as information regarding the state of the vibration source. 
     Second Embodiment 
     Next, a disk device  200  according to a second embodiment will be described. Hereinafter, portions different from those of the first embodiment will be mainly described. 
     In the first embodiment, a configuration and an operation in a case where the disk device  100  includes one actuator are exemplified, and in the second embodiment, a configuration (multi-actuator configuration) and an operation in a case where the disk device  200  includes plural actuators are exemplified. 
     The disk device  200  can be configured as illustrated in  FIG.  8   .  FIG.  8    is a diagram illustrating a configuration of the disk device  200 , in which a part of the configuration of the disk device  200  is illustrated in a cross-sectional view and the other part is illustrated in a block diagram. 
     The disk device  200  further includes a disk DK 2 , a head H 2 , a head H 3 , an actuator AC 2 , a controller communication unit  17 , and a controller  52 . The controller  5  corresponds to the actuator AC 1 , and the controller  52  corresponds to the actuator AC 2 . Thus, the actuator AC 1  and the actuator AC 2  can be controlled independently of each other. 
     The disk DK 2  is a substantially disk-shaped medium similar to the disk DK 1  (see  FIG.  2   ), and is supported rotatably around the Z axis by the base of the housing  1  via the spindle  10  together with the disk DK 1 . The disk DK 2  is disposed between the disk DK 1  and the base  1   a  in the Z direction. The disk DK 2  has a recording surface M 2  on the +Z side and a recording surface M 3  on the −Z side. 
     The head H 2  is held by the actuator AC 2  and disposed so as to face the recording surface M 2  of the disk DK 2 . The head H 3  is held by the actuator AC 2  and disposed so as to face the recording surface M 3  of the disk DK 2 . Each of the heads H 2  and H 3  includes a write head and a read head. The actuator AC 2  moves the heads H 2  and H 3  with respect to the recording surfaces M 2  and M 3  at the time of seek or the like, and positions the heads H 2  and H 3  to one of the plural tracks TR. 
     The plural actuators AC 1  and AC 2  are configured to be drivable independently of each other. The actuator AC 2  includes a voice coil motor (VCM)  42  and actuator arms AM 2  and AM 3 . The head H 2  is provided at a position on the disk DK 2  side (recording surface M 2  side) at a distal end of the actuator arm AM 2 . The head H 3  is provided at a position on the disk DK 2  side (recording surface M 3  side) at the distal end of the actuator arm AM 2 . 
     Note that the actuator AC 2  may further include microactuators MA 2  and MA 3 . In this case, the microactuators MA 2  and MA 3  are provided at the distal ends of the actuator arms AM 2  and AM 3 . The head H 2  is provided at a position on the disk DK 2  side (recording surface M 2  side) at a distal end of the microactuator MA 2 . The head H 3  is provided at a position on the disk DK 2  side (recording surface M 3  side) at a distal end of the microactuator MA 3 . 
     The actuator AC 2  drives the actuator arms AM 2  and AM 3  with the shaft AX 1  (see  FIG.  3   ) as a rotation center by the voice coil motor  42  at the time of seek or the like. In a case where the actuator arms AM 2  and AM 3  are configured to rotate simultaneously, the actuator AC 2  may move and position the heads H 2  and H 3  simultaneously. 
     For example, the actuator AC 2  causes the heads H 2  and H 3  to seek in the horizontal direction on the trajectory T via the actuator arms AM 2  and AM 3 , and positions the heads H 2  and H 3  to the target track TR. The actuator AC 2  causes the heads H 2  and H 3  to track on the target track TR. 
     The controller communication unit  17  mediates communication between the controller  5  and the controller  52 . The controller communication unit  17  includes a communication unit  17 A. The communication unit  17 A includes a vibration-related information communication unit  17 A 1 . 
     Upon receiving a notification request for the vibration-related information from the controller  5 , the communication unit  17 A transfers the notification request to the controller  52 . The controller  52  may hold the vibration-related information or may generate the vibration-related information in response to the notification request. Upon receiving the notification request, the controller  52  supplies the vibration-related information to the vibration-related information communication unit  17 A 1  as a response. The vibration-related information communication unit  17 A 1  transfers the vibration-related information to the controller  5 . 
     Upon receiving the notification request for the vibration-related information from the controller  52 , the communication unit  17 A transfers the notification request to the controller  5 . The controller  5  may hold the vibration-related information or may generate the vibration-related information in response to the notification request. Upon receiving the notification request, the controller  5  supplies the vibration-related information to the vibration-related information communication unit  17 A 1  as a response. The vibration-related information communication unit  17 A 1  transfers the vibration-related information to the controller  52 . 
     The controller  52  is communicably connected to the host system HS, and can perform control according to a command upon receiving the command from the host system HS. 
     The controller  52  includes a head amplifier  62 , a driver  72 , a read/write (R/W) channel  82 , and a hard disk control unit (HDC)  92 . 
     The head amplifier  62  selects the heads H 2  and H 3  and amplifies a signal at the time of writing or detects a signal at the time of reading. The head amplifier  62  includes a write current control unit  62 A, a read signal detection unit  62 B, and a head selection unit  62 C. The head selection unit  62 C selects the head H to be used from the heads H 2  and H 3 . The controller  5  controls and positions the position of the head H with respect to the disk DK 2  on the basis of the servo information read by the selected head H. The write current control unit  62 A controls the write current flowing through the write head in the head H in a state where the head H is positioned. The read signal detection unit  62 B detects a signal read by the read head in the head H in a state where the head H is positioned. The head amplifier  62  can be implemented as an integrated circuit (IC). 
     The driver  72  drives the voice coil motor  42  and the spindle motor  3 , and takes in a rotational vibration (RV) signal from the RV sensors  11 A and  11 B. The driver  72  includes a spindle motor (SPM) control unit  72 A, a voice coil motor (VCM) control unit  72 B, and an RV signal capturing unit  72 D. The spindle motor control unit  72 A controls rotation of the spindle motor  3 . The voice coil motor control unit  72 B controls driving of the voice coil motor  42 . The RV signal capturing unit  72 D captures rotational vibration signals (RV signals) from the RV sensors  11 A and  11 B. 
     Note that, in a case where the actuator AC 2  further includes the microactuators MA 2  and MA 3 , the driver  72  further includes a microactuator (MA) control unit  7 C. The microactuator (MA) control unit  7 C controls driving of the microactuators MA 2  and MA 3 . Thus, the position of the head H can be finely adjusted. 
     The read/write channel  82  exchanges data between the head amplifier  62  and the hard disk control unit  92 . Note that the data includes read data, write data, and the servo information. The read/write channel  82  includes a write prohibition unit  82 A. The write prohibition unit  82 A includes a sensor write prohibition unit  82 A 1  and an HDC write prohibition unit  82 A 2 . 
     The sensor write prohibition unit  82 A 1  receives a detection result of the write prohibition detector  13 . If the write prohibition has been detected, the sensor write prohibition unit  82 A 1  supplies the write prohibition instruction to the head amplifier  62 . If the write prohibition has not been detected, the sensor write prohibition unit  82 A 1  supplies the write permission instruction to the head amplifier  62 . 
     The HDC write prohibition unit  82 A 2  receives the determination result of the write prohibition determination from the hard disk control unit  92 . If the determination result is write prohibition, the HDC write prohibition unit  82 A 2  supplies the write prohibition instruction to the head amplifier  62 . If the determination result is write permission, the HDC write prohibition unit  82 A 2  supplies the write permission instruction to the head amplifier  62 . 
     When receiving the write prohibition instruction from at least one of the sensor write prohibition unit  82 A 1  or the HDC write prohibition unit  82 A 2 , the head amplifier  62  prevents the write operation to the disk DK 2  by the head H from being performed. That is, the write current control unit  62 A prevents the write current from flowing through the write head in the head H. 
     When the head amplifier  62  receives the write permission instruction from both the sensor write prohibition unit  82 A 1  and the HDC write prohibition unit  82 A 2 , the write operation to the disk DK 2  by the head H is performed. That is, the write current control unit  62 A controls the write current flowing through the write head in the head H in a state where the head H is positioned. 
     The hard disk control unit  92  performs write control and read control on the basis of a write command and a read command from the outside of the disk device  100  (for example, host system HS), and exchanges data between the outside and the read/write channel  82 . The configuration including the driver  72 , the read/write channel  82 , and the hard disk control unit  92  can be implemented as a system-on-chip. 
     The hard disk control unit  92  includes a command control unit  92 A and a servo control unit  92 B. The command control unit  922 A controls an operation according to a command received from the host system HS. The command control unit  92 A includes a command selection unit  92 A 1 . When the hard disk control unit  92  receives a command from the host system HS, the command selection unit  92 A 1  recognizes the received command and selects the control operation according to the recognized command. The command selection unit  92 A 1  specifies an address or the like included in the command. 
     In a case where the command is a write command, the command selection unit  92 A 1  selects write control according to the write command. The command selection unit  92 A 1  specifies each of the write address and ride data included in the write command. 
     The servo control unit  92 B controls the position of the head H according to the control operation selected by the command selection unit  92 A 1 . A tracking control unit  92 B 1 , a seek control unit  92 B 2 , and a write operation determination unit  92 B 3  are included. 
     The seek control unit  92 B 2  controls the seek operation of the head H to the target track TR on the disk DK 2  according to the address (for example, the write address) included in the command. The seek control unit  92 B 2  controls the actuator AC 2  via the read/write channel  82  and the head amplifier  62 , causes the head H to seek in the horizontal direction on the trajectory T via the actuator arm AM, and positions the head H to the target track TR. The target track is the track TR corresponding to the address (for example, the write address) included in the command. 
     The tracking control unit  92 B 1  controls tracking operation of the head H on the target track TR of the disk DK 2 . The tracking control unit  92 B 1  controls the actuator AC 2  via the read/write channel  82  and the head amplifier  62 , and causes the head H to track on the target track TR via the actuator arm AM. 
     Here, the hard disk control unit  92  has a function of performing write prohibition determination in a case where the command is a write command. In a state where the head H is positioned and caused to track on the target track TR according to the write address, the write operation determination unit  92 B 3  performs the write prohibition determination. There are several types of write prohibition determination, and the types include a write prohibition determination based on a current position and a write prohibition determination based on a predicted position. The write operation determination unit  92 B 3  includes a position operation determination unit  92 B 31  and a predicted position operation determination unit  92 B 32 . The position operation determination unit  92 B 31  performs the write prohibition determination based on the current position, and the predicted position operation determination unit  92 B 32  performs the write prohibition determination based on the predicted position. 
     The servo control unit  92 B demodulates the position error signal according to the servo information read from the servo region via the head H. The position error signal indicates a relative position of the head H from the center of the track TR. The servo control unit  92 B obtains a current actual position of the head H and a velocity component immediately before reaching the current actual position according to the position error signal. The servo control unit  92 B may obtain the current actual position of the head H as an absolute value of a current displacement from the center of the track TR of the head H. The servo control unit  92 B estimates a future predicted position according to the current actual position of the head H and the velocity component immediately before reaching the current actual position. The servo control unit  92 B may obtain the future predicted position of the head H as an absolute value of a future displacement from the center of the track TR of the head H. 
     The predicted position operation determination unit  92 B 32  performs the write prohibition determination according to the predicted position. The predicted position operation determination unit  92 B 32  determines that writing is possible when the estimated predicted position is equal to or less than a threshold, and determines that writing is not possible when the estimated predicted position has exceeded the threshold. The servo control unit  92 B performs the write operation on the disk DK 2  by the head H if the predicted position operation determination unit  92 B 32  determines that writing is possible, and does not perform the write operation on the disk DK 2  by the head H if the predicted position operation determination unit  92 B 32  determines that writing is not possible. In order to prevent the shifted writing in which data is written out of the target track TR, it is desirable that the estimated value of the predicted position used for the write prohibition determination is accurate. 
     For example, it is assumed that the servo control unit  92 B causes the head H to track on the target track TR. Assuming that the actual position measured with the servo information read by the head H is represented by p and the predicted position predicted by the servo control unit  9 B is represented by p{circumflex over ( )}, the write prohibition determination based on the predicted position can be performed depending on whether or not the inequality of Mathematical Expression 3 or Mathematical Expression 4 is satisfied. 
     The point that the appropriate values (for example, optimum values) of the coefficients a and b used for estimating the predicted position can fluctuate due to the influence of the vibration received by the actuators AC 1  and AC 2  is similar to the first embodiment, but in a case of the multi-actuator configuration, the influence of the operation state of another actuator is larger than the disturbance. Although the actuators AC 1  and AC 2  affect each other, here, the actuator AC executing the affected write operation is referred to as a victim, and the affecting actuator AC is referred to as an aggressor. 
     In a case where the aggressor performs a seek operation, the manner of influence varies depending on the shape of a VCM current flowing through the voice coil motor (VCM). The VCM current at the time of seek is referred to as a seek current. A position error on the victim side at this time is represented by 
       (position error)=(aggressor current)×(cross transfer function)×(victim sensitivity function).
 
     The aggressor current is the VCM current on the aggressor side (seek current at the time of seek). The cross transfer function is a transfer function from the aggressor current to the victim side head. The victim sensitivity function is a function indicating feedback characteristics of the VCM current on the victim side. 
     The controller  52  of the actuator AC 2  and the controller  5  of the actuator AC 1  are functionally configured as illustrated in  FIG.  9   . The controller  52  includes a subtractor  521 , a CTLR  522 , a notch  523 , an LS  524 , an adder  525 , a GMA  526 , a notch  527 , and an adder  530 . The controller  5  includes a subtractor  501 , a CTLR  502 , a notch  503 , an LS  506 , an adder  507 , a GMA  508 , a notch  509 , and an adder  510 . 
     A cross transfer function between the voice coil motor  42  of the actuator AC 2  and the voice coil motor  4  of the actuator AC 1  is represented by A ct . In the controller  52 , the position error signal generated by subtracting the head position signal POS from the servo position by the subtractor  521  is represented by p 2 , the current supplied from the notch  527  to the voice coil motor  42  of the actuator AC 2  is represented by I 2 , and the feedback characteristic from the voice coil motor  42  to the subtractor  521  is represented by F B2 . In the controller  5 , the position error signal generated by subtracting the head position signal POS from the servo position by the subtractor  501  is represented by p 1 , the current supplied from the notch  509  to the voice coil motor  4  of the actuator AC 1  is represented by I 1 , and the feedback characteristic from the voice coil motor  4  to the subtractor  501  is represented by F B1 . 
     For example, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , since the aggressor current is I 2 , the cross transfer function is A ct , and the victim sensitivity function is F B1 , the position error signal p 1  of the head H (head H 0  or head H 1 ) of the actuator AC 1  is represented by the following Mathematical Expression 7. 
         p   1   =I   2   ×A   ct   ×F   B1   Mathematical Expression 7
 
     Alternatively, in a case where the aggressor=actuator AC 1  and the victim=actuator AC 2 , since the aggressor current is I 1 , the cross transfer function is A ct , and the victim sensitivity function is F B2 , the position error signal p 2  of the head H (head H 2  or head H 3 ) of the actuator AC 2  is represented by the following Mathematical Expression 8. 
         p   2   =I   1   ×A   ct   ×F   B2   Mathematical Expression 8
 
     In the multi-actuator configuration, the frequency of vibration received by the actuator AC on the victim side may fluctuate according to the operation mode. The frequency of the vibration received by the actuator AC on the victim side appears as the frequency of the fluctuation of the position error signal of the head H on the victim side. 
     For example, in a case where the aggressor side performs a seek operation, the waveform of the aggressor current depends on a seek control method of the seek operation. The seek control method includes a long distance seek and a short distance seek. The long distance seek is a control method in which a moving distance of the head H to seek is relatively long, and the short distance seek is a control method in which a moving distance of the head H to seek is relatively short. A frequency component (that is, the frequency of vibration on the aggressor side) that the seek current has may be greatly different depending on a seek distance. 
     In a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , and the seek control method of the aggressor is the long distance seek, the seek current on the aggressor side changes with a relatively large amplitude as illustrated in  FIG.  10 A  in response to the relatively long seek distance. In response to this, the position error signal of the head H 1  on the victim side fluctuates at a relatively slow frequency as illustrated in  FIG.  10 B .  FIGS.  10 A and  10 B  are diagrams illustrating changes in the seek current and the position error signal, respectively, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , and the seek control method of the aggressor is the long distance seek. The vertical axis in  FIG.  10 A  represents the level of the seek current, the vertical axis in  FIG.  10 B  represents the level of the position error signal, and the horizontal axes in  FIGS.  10 A and  10 B  each represent time. 
     On the other hand, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , and the seek control method of the aggressor is the short distance seek, the seek current on the aggressor side changes with a relatively small amplitude as illustrated in  FIG.  10 C  in response to the relatively short seek distance. In response to this, the position error signal of the head H 1  on the victim side fluctuates at a relatively fast frequency as illustrated in  FIG.  10 D .  FIGS.  10 C and  10 D  are diagrams illustrating changes in the seek current and the position error signal, respectively, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , and the seek control method of the aggressor is the short distance seek. The vertical axis in  FIG.  10 C  represents the level of the seek current, the vertical axis in  FIG.  10 D  represents the level of the position error signal, and the horizontal axes in  FIGS.  10 C and  10 D  each represent time. 
     The long distance seek uses velocity feedback control in which the velocity of the head H (first-order differential value of the head position signal POS) follows the target velocity and mode switching control in which a seek mode (acceleration mode, constant velocity mode, and deceleration mode) is switched. The short distance seek uses position feedback control in which the position of the head H (head position signal POS) follows the target position trajectory and feedforward control in which the seek current (VCM current I 1  or I 2 ) is generated according to a predetermined characteristic. Mode switching control may be further used in the short distance seek. In the mode switching control, there is a possibility that the frequency component that the seek current has greatly differs at each stage of the seek control. Each stage of the seek control includes a rise of a seek current waveform in the acceleration mode, a fall of the seek current waveform in the acceleration mode, a rise of a seek current waveform in the deceleration mode, and a fall of the seek current waveform in the deceleration mode. 
     For example, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , and the seek control method of the aggressor is the long distance seek, the acceleration mode, the constant velocity mode, and the deceleration mode are switched in periods TP 1 , TP 2 , and TP 3  illustrated in  FIG.  10    A, respectively. 
     When the seek current waveform rises in the aggressor period TP 1  (acceleration mode), the position error signal of the head H 1  on the victim side fluctuates at a relatively fast frequency as illustrated in  FIG.  10 B . When the seek current waveform falls in the aggressor period TP 1 , the position error signal of the head H 1  on the victim side fluctuates at a relatively slow frequency as illustrated in  FIG.  10 B . 
     When the seek current waveform rises in the aggressor period TP 3  (deceleration mode), the position error signal of the head H 1  on the victim side fluctuates at a relatively fast frequency as illustrated in  FIG.  10 B . When the seek current waveform falls in the aggressor period TP 3 , the position error signal of the head H 1  on the victim side fluctuates at a relatively slow frequency as illustrated in  FIG.  10 B . 
     Further, the cross transfer function greatly varies depending on a Z position of the head H. For example, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , as illustrated in  FIG.  11   , the head H 1  positioned in the middle of the shaft AX 1  in the Z direction vibrates at a relatively slow frequency F H1  in response to a large mode caused by bending of the shaft AX 1  (see  FIG.  3   ). On the other hand, the head H 0  close to the uppermost position in the Z direction of the shaft AX 1  vibrates at a relatively fast frequency F H0  in response to almost no observation of the mode.  FIG.  11    is a diagram illustrating a difference in transmission characteristics of vibration for each head. 
     In a case where the aggressor=actuator AC 1  and the victim=actuator AC 2 , although not illustrated, the head H 2  (see  FIG.  8   ) positioned in the middle of the shaft AX 1  in the Z direction vibrates at a relatively slow frequency in response to a large mode caused by bending of the shaft AX 1  (see  FIG.  3   ). On the other hand, the head H 3  close to the lowermost side in the Z direction of the shaft AX 1  vibrates at a relatively fast frequency according to the fact that the mode is hardly observed. 
     For example, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , with respect to the change in the seek current on the aggressor side illustrated in  FIG.  12 A , the head H 0  on the victim side fluctuates at a relatively fast frequency as illustrated in  FIG.  12 B  according to the position at the uppermost position in the Z direction of the shaft AX 1 .  FIGS.  12 A and  12 B  are diagrams illustrating changes in the seek current and the position error signal, respectively, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 . The vertical axis in  FIG.  12 A  represents the level of the seek current, the vertical axis in  FIG.  12 B  represents the level of the position error signal, and the horizontal axes in  FIGS.  12 A and  12 B  each represent time. 
     In a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 , with respect to the change in the seek current on the aggressor side illustrated in  FIG.  12 C , the head H 1  on the victim side fluctuates at a relatively slow frequency as illustrated in  FIG.  12 D  according to the position in the middle in the Z direction of the shaft AX 1 .  FIGS.  12 C and  12 D  are diagrams illustrating changes in the seek current and the position error signal, respectively, in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 . The vertical axis in  FIG.  12 C  represents the level of the seek current, the vertical axis in  FIG.  12 D  represents the level of the position error signal, and the horizontal axes in  FIGS.  12 C and  12 D  each represent time. 
     Thus, the predicted position coefficient updating units  9 B 4  and  92 B 4  of the controllers  5  and  52  acquire operation mode information as the information regarding the state of the vibration source. The predicted position coefficient updating units  9 B 4  and  92 B 4  change the values of the coefficients a and b for estimating the predicted position of the head H for each head H according to the operation mode information. 
     For example, coefficient information as illustrated in  FIGS.  13 A and  13 B  may be stored in the nonvolatile memory  16 , the disk DK 1 , or the disk DK 2 .  FIGS.  13 A and  13 B  are diagrams illustrating a data structure of coefficient information.  FIG.  13 A  illustrates an operation mode definition table as a part of the coefficient information, and  FIG.  13 B  illustrates a predicted position coefficient table as another part of the coefficient information. In  FIG.  13 B , the coefficients are indicated by a(head identifier, operation mode) and b(head identifier, operation mode). 
     In the operation mode definition table illustrated in  FIG.  13 A , the operation state and the operation mode are associated with each other for plural operation states. For example, an operation state “in tracking” is defined as an operation mode “0”. An operation state “fan vibrating” is defined as an operation mode “1”. An operation state “acceleration rise in seeking” is defined as an operation mode “2”. An operation state “acceleration fall in seeking” is defined as an operation mode “3”. An operation state “constant velocity in seeking” is defined as an operation mode “4”. An operation state “deceleration rise in seeking” is defined as an operation mode “5”. An operation state “deceleration fall in seeking” is defined as an operation mode “6”. An operation state “in settling” is a state after seeking until the position of the head H becomes stable, and is defined as an operation mode “M”. M is an arbitrary integer of seven or more. 
     In the predicted position coefficient table illustrated in  FIG.  13 B , a head identifier (for example, the head number), an operation mode, and a predicted position coefficient are associated with each head for plural operation modes. For the head H 0  with the head identifier “0”, the coefficients a(0, 0) and b(0, 0) correspond to the operation mode “0”, and the coefficients a(0, M) and b(0, M) correspond to the operation mode “M”. For the head H 1  with the head identifier “1”, the coefficients a(1, 0) and b(1, 0) correspond to the operation mode “0”, and the coefficients a(1, M) and b(1, M) correspond to the operation mode “M”. 
     Here, with respect to the operation state on the aggressor side, the controller controlling the aggressor side can grasp the state in the past, the present, and the future slightly ahead. Accordingly, the controller on the aggressor side notifies the controller on the victim side of the operation state on the aggressor side. The controller on the victim side can estimate the predicted position by switching the coefficients a and b to be used according to each situation. Thus, it is possible to minimize the performance deterioration while preventing the shifted writing. 
     Next, the operation of the disk device  200  will be described with reference to  FIG.  14   .  FIG.  14    is a flowchart illustrating an operation in seeking of the disk device  200 .  FIG.  14    illustrates an operation of the controller  52  on the aggressor side in seeking in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 . The disk device  200  can perform the operation illustrated in  FIG.  14    as interrupt processing for each sample timing while the head H is in seeking. 
     The controller  52  calculates the actual position of the head H by the servo demodulation in seeking (S 31 ). The controller  52  reads the servo information from the servo region SR via the read head of the head H. The controller  52  demodulates the position error signal according to the servo information. The position error signal indicates a relative position of the head H from the center of the track TR. The controller  52  obtains the current actual position of the head H according to the position error signal. 
     The controller  52  acquires the detection results of the sensors such as the RV sensors  11 A and  11 B via the controller  5  and the controller communication unit  17 , and estimates the vibration state of the vibration source according to the detection results of the sensors (S 32 ). The controller  52  may estimate the amplitude and direction of vibration as the state of the vibration source. The controller  52  determines a vibration control instruction value so as to suppress vibration according to the estimated vibration state (S 33 ), and performs control according to the vibration control instruction value (S 34 ). As the control, the controller  52  may perform vibration control to vibrate the actuator AC 2  so as to cancel the influence of vibration. The controller  52  performs switching determination of the seek mode according to the progress state of the seek control (S 35 ). For example, if the current seek mode is the acceleration mode, the controller  52  determines whether or not to switch from the acceleration mode to the constant velocity mode. If the current seek mode is the constant velocity mode, the controller  52  determines whether or not to switch from the constant velocity mode to the deceleration mode. The controller  52  notifies the controller  5  on the victim side of the operation mode information as necessary (S 36 ). For example, in a case where it is determined in S 35  to switch from the acceleration mode to the constant velocity mode, the controller  52  notifies the controller  5  of the operation mode information indicating that the seek mode after switching is the constant velocity mode. In a case where it is determined in S 35  to switch from the constant velocity mode to the deceleration mode, the controller  52  notifies the controller  5  of the operation mode information indicating that the seek mode after switching is the deceleration mode. 
     Another operation of the disk device  200  will be described with reference to  FIG.  15   .  FIG.  15    is a flowchart illustrating an operation in tracking of the disk device  200 . A left diagram of  FIG.  15    illustrates an operation of the controller  52  on the aggressor side in an arbitrary state in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 . The controller  52  can perform the operation illustrated in the left diagram of  FIG.  15    as interrupt processing for each sample timing in an arbitrary state. A right diagram of  FIG.  15    illustrates the operation of the controller  5  on the victim side in tracking in a case where the aggressor=actuator AC 2  and the victim=actuator AC 1 . The controller  5  can perform the operation illustrated in the right diagram of  FIG.  15    as interrupt processing for each sample timing in a state where the head H is made to track on the target track TR. 
     After performing the processing of S 1  and S 2 , the controller  5  checks the operation mode of the other actuator AC (S 41 ). The controller  5  transmits a transmission request for the operation mode information to the controller  52  via the controller communication unit  17 . The controller  52  waits until the transmission request for the operation mode information is received (No in S 51 ), and transmits, upon receiving the transmission request for the operation mode information (Yes in S 51 ), the operation mode information of the actuator AC 2  to the controller  5  via the controller communication unit  17  (S 52 ). The controller  5  receives the operation mode information. The controller  5  estimates the vibration state of the vibration source according to the operation mode information (S 42 ). The operation mode information is information indicating an operation state of the actuator AC 2 . 
     After performing the processing of S 5  and S 6 , the controller  5  performs predicted position coefficient update processing (S 43 ). The controller  5  may perform the processes of S 61  to S 62  illustrated in  FIG.  16    as the predicted position coefficient update processing.  FIG.  16    is a flowchart illustrating the predicted position coefficient update processing. 
     The controller  5  checks the operation mode of the other actuator AC (S 61 ). The controller  5  transmits a transmission request for the operation mode information to the controller  52  via the controller communication unit  17 . The controller  52  waits until the transmission request for the operation mode information is received (No in S 53 ), and transmits, upon receiving the transmission request for the operation mode information (Yes in S 53 ), the operation mode information of the actuator AC 2  to the controller  5  via the controller communication unit  17  (S 54 ). The controller  5  receives the operation mode information. 
     The controller  5  updates the values of the coefficients a and b for obtaining the predicted position for each head H according to the operation mode information (S 62 ). The controller  5  may update the values of the coefficients a and b with reference to the coefficient information as illustrated in  FIGS.  13 A and  13 B  according to the operation mode of the actuator AC 2  indicated by the operation mode information. 
     For example, when the heads H 0  and H 1  are in tracking by the actuator AC 2 , the predicted position coefficient updating unit  9 B 4  refers to the operation mode definition table illustrated in  FIG.  13 A  and specifies the operation mode as “0”. The predicted position coefficient updating unit  9 B 4  refers to the predicted position coefficient table illustrated in  FIG.  13 B , updates the coefficients of the head H 0  to a(0, 0) and b(0, 0) corresponding to the operation mode “0”, and updates the coefficients of the head H 1  to a(1, 0) and b(1, 0) corresponding to the operation mode “0”. 
     Alternatively, when the waveform rises in the acceleration mode while the heads H 0  and H 1  are in seeking by the actuator AC 2 , the predicted position coefficient updating unit  9 B 4  refers to the operation mode definition table illustrated in  FIG.  13 A  and specifies the operation mode as “2”. The predicted position coefficient updating unit  9 B 4  refers to the predicted position coefficient table illustrated in  FIG.  13 B , updates the coefficients of the head H 0  to a(0, 2) and b(0, 2) corresponding to the operation mode “0”, and updates the coefficients of the head H 1  to a(1, 2) and b(1, 2) corresponding to the operation mode “0”. 
     Thereafter, as illustrated in  FIG.  15   , the controller  5  performs the processing of S 8  and subsequent steps. 
     As described above, in the second embodiment, in the disk device  200 , the controller  5  acquires information regarding the operation state of the other actuator, changes the value of the coefficient for estimating the predicted position of the head H according to the information regarding the operation state of the other actuator, and estimates the predicted position of the head H with the changed value of the coefficient. In this manner, the estimation accuracy of the predicted position can be improved, and thus the accuracy of the write prohibition determination based on the predicted position can be improved. Consequently, it is possible to secure a period during which the head H can properly perform the write operation in the target track TR while preventing the shifted writing in which the head H protrudes from the target track TR to the adjacent track TR and overwrites thereon. That is, in a case where vibration is generated, both improvement in reliability and improvement in performance of the write operation can be achieved, and the write operation can be appropriately performed. 
     Note that the information regarding the operation state of the other actuator acquired by the controller on the victim side at the time of coefficient update may include information regarding a seek control method or information regarding a seek distance. The information regarding the seek control method includes information indicating whether the seek control method of the other actuator is the long distance seek or the short distance seek. The information regarding the seek distance includes information indicating whether the seek distance of the other actuator is a seek distance corresponding to the long distance seek or a seek distance corresponding to the short distance seek. 
     Alternatively, the information regarding the operation state of the other actuator acquired by the controller on the victim side at the time of coefficient update may be a first-order differential value of a seek current of the other actuator. In this case, the controller on the victim side may estimate the frequency of vibration according to the first-order differential value of the seek current of the other actuator, and update the coefficients a and b with reference to the coefficient information illustrated in  FIGS.  5 A and  5 B . 
     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.