Magnetic disk device

Abstract

Provided is a magnetic disk device having high positioning accuracy. A controller of a disk device according to an embodiment corrects an instruction value of a VCM current by first feed-forward control based on a first detection value of a first sensor. The controller executes a first operation in accordance with the occurrence of the set event. In the first operation, the controller acquires a first waveform, which is a waveform of a deviation amount of a detected position of the magnetic head from a target position of the magnetic head, and acquires a first frequency band, which is a frequency band having an amplitude greater than a first threshold value, from the first waveform. The controller adjusts a coefficient of a transfer function of the first feed-forward control such that the first detection value is suppressed in a second frequency band different from the first frequency band and a correction amount for the first instruction value is output on the basis of the first detection value in the first frequency band.

Description

[0001] This application claims the benefit of priority based on Japanese Patent Application No. 2024-031640 (filing date: March 1, 2024), the entire contents of which are incorporated herein by reference. Technical Field

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

[0003] In a magnetic disk drive, a voice coil motor (VCM) moves the magnetic head radially around the magnetic disk. To minimize the effects of disturbances on the positioning accuracy of the magnetic head, feedforward control is sometimes performed on the indicated value of the current driving the VCM based on various sensor values. Summary of the Invention

[0004] An embodiment of the present invention provides a magnetic disk device with high positioning accuracy.

[0005] The magnetic disk device of this embodiment includes a magnetic disk, a magnetic head, an actuator arm, a motor, a drive circuit, a first sensor, and a controller. The magnetic head writes data to and reads data from the magnetic disk. The magnetic head is arranged at the front end of the actuator arm. The motor moves the magnetic head in the radial direction of the magnetic disk by moving the actuator arm. The drive circuit generates a first current for driving the motor in an amount corresponding to an indication value and supplies the generated first current to the motor. The first sensor detects a predetermined physical quantity. The controller detects the position of the magnetic head and generates a first indication value in a manner that reduces the deviation of the detection position of the magnetic head from the target position of the magnetic head. The controller corrects the first indication value through a first feedforward control based on the first detection value of the first sensor and inputs a second indication value, which is the corrected first indication value, as the indication value to the drive circuit. The controller performs a first action in response to the occurrence of a set event. In the first action, the controller adjusts the coefficient of the transfer function of the first feedforward control through the following action. Specifically, the controller obtains a first waveform as a waveform of the deviation amount, and obtains a first frequency band as a frequency band having an amplitude greater than a first threshold value from the first waveform. The controller adjusts the coefficients of the transfer function of the first feedforward control so that the first detection value is suppressed in a second frequency band different from the first frequency band, and a correction amount to the first indication value is output based on the first detection value in the first frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0008] Figure 3This is a diagram showing an example of a control block for a seek operation included in the magnetic disk device according to the embodiment.

[0009] Figure 4 This is a flowchart showing an example of the operation of the magnetic disk device according to the embodiment.

[0010] Figure 5 1 and 2 are diagrams showing examples of various waveforms obtained in the magnetic disk device according to the embodiment.

[0011] Figure 6 (A) and (B) are diagrams for explaining an example of a method of adjusting the coefficients of the numerator and the denominator of the IIR type transfer function of the FF controller according to the embodiment.

[0012] Description of Reference Numerals

[0013] 1 Magnetic disk device, 2 Host, 11 Magnetic disk, 12 Spindle motor, 13 Ramp, 15 Actuator arm, 16 VCM, 17a First vibration sensor, 17b Second vibration sensor, 21 Motor driver IC, 22 Magnetic head, 22r Read element, 22w Write element, 23 HDC, 24 Head IC, 25 RWC, 26 Processor, 27 RAM, 28 FROM, 29 Buffer memory, 30 Controller, 41 Servo area, 42 Data area, 50 Track, 101 Target speed table, 102 VCM controller, 103 VCM driver, 104 VCM current detector, 105 FF controller adjustment mechanism, 106 First FF controller, 107 Second FF controller, 108 Third FF controller, 109 Head speed estimator, 110 Settling determination mechanism, 111, 112, 113, 114 Adders. DETAILED DESCRIPTION

[0014] Hereinafter, the magnetic disk device according to the embodiment will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

[0015] (Implementation Method)

[0016] Figure 1 This is a schematic diagram showing an example of the configuration of the magnetic disk device 1 according to the embodiment.

[0017] The magnetic disk device 1 is connected to a host computer 2. The magnetic disk device 1 can receive access commands such as a write command and a read command from the host computer 2.

[0018] The magnetic disk device 1 includes a magnetic disk 11 having a magnetic layer formed on its surface. The magnetic disk device 1 writes data to the magnetic disk 11 or reads data from the magnetic disk 11 in response to an access command.

[0019] Data is written and read via the magnetic head 22. The magnetic disk device 1 includes, in addition to the magnetic disk 11, a spindle motor 12, a ramp 13, an actuator arm 15, a voice coil motor (VCM) 16, a first vibration sensor 17a, a second vibration sensor 17b, a motor driver IC (Integrated Circuit) 21, a magnetic head 22, a hard disk controller (HDC) 23, a head IC 24, a read / write channel (RWC) 25, a processor 26, a RAM 27, a FROM (Flash Read Only Memory) 28, and a buffer memory 29.

[0020] The magnetic disk 11 is rotated at a predetermined rotational speed by a coaxially mounted spindle motor 12 , which is driven by a motor driver IC 21 .

[0021] The motor driver IC 21 drives the spindle motor 12 and the VCM 16 under the control of the processor 26. Specifically, regarding the VCM 16, the motor driver IC 21 receives an instruction value regarding the current to be supplied to the VCM 16 from the processor 26 and generates an amount of current corresponding to the instruction value. The motor driver IC 21 then supplies the generated current to the VCM 16. The current supplied to the VCM 16 is referred to as the VCM current. Furthermore, the instruction value regarding the VCM current input from the processor 26 to the motor driver IC 21 is referred to as the VCM current instruction value.

[0022] The magnetic head 22 writes and reads information from the magnetic disk 11 using its write element 22w and read element 22r. The magnetic head 22 is attached to the front end of the actuator arm 15. The actuator arm 15 is moved by the VCM 16, thereby moving the magnetic head 22 in the radial direction of the magnetic disk 11. Alternatively, a plurality of either the write element 22w or the read element 22r of the magnetic head 22, or both, may be provided relative to a single magnetic head 22.

[0023] The VCM 16 is an example of a motor, and the motor driver IC 21 is an example of a drive circuit.

[0024] When the magnetic disk 11 stops rotating, the magnetic head 22 moves onto the ramp 13. The ramp 13 is configured to hold the magnetic head 22 at a position away from the magnetic disk 11.

[0025] During a read operation, the head IC 24 amplifies and outputs a signal read by the magnetic head 22 from the magnetic disk 11, and supplies it to the RWC 25. Furthermore, during a write operation, the head IC 24 amplifies a signal corresponding to data to be written supplied from the RWC 25, and supplies it to the magnetic head 22.

[0026] The HDC 23 controls data transmission and reception with the host computer 2 via the I / F bus, controls the buffer memory 29 , and the like.

[0027] The buffer memory 29 is used as a buffer for data transmitted and received with the host 2. For example, the buffer memory 29 is used to temporarily store data to be written or data read from the magnetic disk 11.

[0028] The buffer memory 29 is composed of a volatile memory capable of high-speed operation. The type of memory constituting the buffer memory 29 is not limited to a specific type. For example, the buffer memory 29 can be composed of DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), or a combination thereof. Furthermore, the buffer memory 29 can also be composed of any non-volatile memory.

[0029] The RWC 25 performs error correction coding and other modulation on the data to be written, which is supplied from the HDC 23, and supplies the modulated data to the head IC 24. Furthermore, the RWC 25 performs error correction-based demodulation on the signal read from the magnetic disk 11 and supplied from the head IC 24, and outputs the demodulated signal as digital data to the HDC 23.

[0030] The processor 26 is, for example, a CPU (Central Processing Unit) and is connected to the first vibration sensor 17 a , the second vibration sensor 17 b , the RAM 27 , the FROM 28 , and the buffer memory 29 .

[0031] FROM 28 is a nonvolatile memory. It stores firmware (program data) and various operating parameters. The operating parameters may include threshold values ​​Th1, Th2, and Th3 described below. Alternatively, the firmware and various operating parameters may be stored in a predetermined area of ​​the magnetic disk 11.

[0032] The RAM 27 is composed of, for example, a DRAM, an SRAM, or a combination thereof, and is used as a memory for operation by the processor 26. The RAM 27 is used as an area for loading firmware and an area for temporarily storing various operation parameters.

[0033] The processor 26 controls the entire magnetic disk device 1 according to the firmware stored in the FROM 28 or the magnetic disk 11. For example, the processor 26 loads the firmware from the FROM 28 or the magnetic disk 11 into the RAM 27 and controls the motor driver IC 21, the head IC 24, the RWC 25, the HDC 23, and the like according to the loaded firmware.

[0034] The first vibration sensor 17a and the second vibration sensor 17b are capable of detecting the amount of vibration. The amount of vibration detected by the vibration sensor 17 is displacement, velocity, acceleration, or any other physical quantity. To suppress the effects of vibrations external to the magnetic disk drive 1 or generated within the magnetic disk drive 1 on the accuracy of positioning control, the processor 26 performs feedforward control of the VCM current indication value based on the detection values ​​of the first vibration sensor 17a and the second vibration sensor 17b. Details of the feedforward control of the VCM current indication value will be described later.

[0035] The configuration including the HDC 23, RWC 25, and processor 26 can also be considered as the controller 30 that controls the operation of the magnetic disk drive 1. In addition to these components, the controller 30 may also include other elements (such as RAM 27, FROM 28, or buffer memory 29). The controller 30 may be a single SoC (System-on-a-Chip) or may be composed of two or more chips.

[0036] In addition, part or all of the functions of the processor 26 may also be implemented by a hardware circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0037] Furthermore, the number of magnetic disks 11 included in the magnetic disk device 1 is not limited to one. Furthermore, the magnetic disk device 1 may include a number of actuator arms 15 and magnetic heads 22 corresponding to the number of magnetic disks 11. Furthermore, when the magnetic disk device 1 includes a plurality of magnetic heads 22, the plurality of magnetic heads 22 may move as a whole, or the plurality of magnetic heads 22 may form a plurality of groups that are independently movable.

[0038] Figure 2 This figure shows an example of the structure of the magnetic disk 11 according to the embodiment. Servo data for positioning the magnetic head 22 is written on the magnetic layer formed on the surface of the magnetic disk 11 by, for example, a servo writer or self-servo writing (SSW).

[0039] exist Figure 2 , as an example of the arrangement of servo areas where servo data is written, servo areas 41 are shown arranged radially. In the circumferential direction, data areas 42 are provided between two servo areas 41. Multiple concentric tracks (e.g., track 50 in this figure) are provided in the radial direction of the magnetic disk 11. The areas on track 50 demarcated by the servo areas 41 are also called servo sectors.

[0040] The servo data includes a servo mark, a Gray code, a pulse train pattern, and a post-code. The servo mark indicates the start of the servo data. The Gray code includes an ID, i.e., a track number, for identifying each track 50 provided on the magnetic disk 11, and an ID, i.e., a servo sector number, for identifying each servo sector (i.e., a servo area 41) on the track 50. The pulse train pattern is data used to detect the positional offset from the center of the track represented by the track number included in the Gray code. The track number included in the Gray code is provided as an integer value, for example, and by demodulating the pulse train pattern, the offset below the decimal point based on the position represented by the track number can be obtained. In other words, by demodulating the pulse train pattern, the current position of the magnetic head 22 in the radial direction can be obtained. The post-code is data used to correct the positional offset of the shape of the track 50 specified by the Gray code and the pulse train pattern from the ideal shape of the track 50.

[0041] When writing data to or reading data from the magnetic disk 11, the controller 30 performs positioning control of the magnetic head 22 based on the servo data read by the magnetic head 22 from the servo area 41. During the positioning control, the controller 30 generates a VCM current indication value in such a manner that the deviation of the detection position of the magnetic head 22 from the target position of the magnetic head 22 (hereinafter referred to as the position deviation) is reduced.

[0042] Positioning control includes control of seek and tracking operations. Seek is the operation of moving the magnetic head 22 radially toward a target track. Tracking is the operation of maintaining the magnetic head 22 on the target track.

[0043] During the seek operation, the controller 30 performs a seek stabilization operation. The seek stabilization operation determines whether access (i.e., writing or reading) to the magnetic disk 11 can be initiated based on the amount of position deviation. In one example, the seek stabilization operation determines whether the amount of position deviation has remained within a set range for a predetermined period of time. If it is confirmed that the amount of position deviation has remained within the set range for a predetermined period of time, the seek stabilization operation (and the seek operation) is completed, and the tracking operation begins. Under the control of the tracking operation, writing or reading from the magnetic disk 11 begins.

[0044] In the embodiment, the controller 30 performs feedforward control on the VCM current indication value during the seek operation. By performing feedforward control on the VCM current indication value, the controller 30 suppresses the influence of disturbances such as vibration on positioning accuracy during the seek operation.

[0045] Furthermore, feedforward control of the VCM current indication value may be performed based on the detection values ​​of the first vibration sensor 17a and the second vibration sensor 17b described above, or based on the detection values ​​of any sensor in place of these detection values. Here, as an example, feedforward control of the VCM current indication value is performed based on the detection values ​​of the first vibration sensor 17a, the detection value of the second vibration sensor 17b, and the detection value of the VCM current supplied to the VCM 16.

[0046] Hereinafter, the detection value of the first vibration sensor 17a is referred to as a first vibration detection value. The detection value of the second vibration sensor 17b is referred to as a second vibration detection value. The detection value of the VCM current supplied to the VCM 16 is referred to as a VCM current detection value.

[0047] Figure 3 This is a diagram showing an example of a control block for a seek operation included in the magnetic disk device 1 according to the embodiment.

[0048] The magnetic disk device 1 includes a target speed table 101, a VCM controller 102, a VCM driver 103, a VCM current detector 104, an FF (Feed Forward) controller adjustment mechanism 105, a first FF controller 106, a second FF controller 107, a third FF controller 108, a head speed estimator 109, a stability determination mechanism 110, and four adders 111 to 114.

[0049] The target speed table 101 is stored in, for example, FROM 28 and is read by the processor 26. The VCM controller 102, FF controller adjustment mechanism 105, first FF controller 106, second FF controller 107, third FF controller 108, head speed estimator 109, stability determination mechanism 110, and four adders 111 to 114 are implemented by the processor 26. The VCM driver 103 and the VCM current detector 104 are provided in the motor driver IC 21.

[0050] In the description of this specification, addition is assumed to include not only addition of positive values ​​but also addition of negative values, that is, subtraction. In other words, some or all of the four adders 111 to 114 may perform subtraction.

[0051] The magnetic disk drive 1 controls the control object Ctgt through these functional components. The control object Ctgt includes the VCM 16, the actuator arm 15, the magnetic head 22, the head IC 24, and the RWC 25. The processor 26 detects the current radial position of the magnetic head 22 based on the servo data read from the servo sector and obtains the detected position.

[0052] The processor 26 also obtains a target position Ptgt as a target position in the radial direction through a predetermined calculation. The adder 111 obtains a position deviation amount in the radial direction by subtracting the detected position from the target position Ptgt.

[0053] The processor 26 obtains the target speed in the radial direction of the magnetic head 22 based on the position deviation amount and the target speed table 101 .

[0054] The target speed table 101 is information that specifies the relationship between the seek distance and the target speed in the radial direction of the magnetic head 22. The seek distance is the distance in the radial direction from the current position of the magnetic head 22 to the target track. According to the target speed table 101, the relationship between the seek distance and the target speed of the magnetic head 22 is specified, for example, such that the longer the seek distance, the faster the target speed of the magnetic head 22. The processor 26 searches the target speed table 101 using the position deviation as the seek distance to obtain the target speed of the magnetic head 22 corresponding to the position deviation.

[0055] The target speed table 101 may be information in a tabular form or may be configured as a mathematical expression. In addition, the processor 26 may be configured to further fine-tune the target speed obtained based on the target speed table 101 .

[0056] The speed of the magnetic head 22 and the speed of the VCM 16 can be easily converted to each other. Therefore, the target speed can also be expressed as the motor speed of the VCM 16. In the following description, it is assumed that the speed (including the target speed, etc.) represents the speed in the radial direction of the magnetic head 22. In addition, the speed of the magnetic head 22 represents the speed in the radial direction of the magnetic head 22.

[0057] The head velocity estimator 109 estimates the velocity of the magnetic head 22 based on the positional deviation amount and the VCM current indication value.

[0058] The adder 112 obtains the speed deviation amount by subtracting the estimated value of the speed of the magnetic head 22 obtained by the head speed estimator 109 from the target speed.

[0059] The VCM controller 102 calculates the VCM current command value based on the speed deviation. The VCM controller 102 calculates the VCM current command value so as to minimize the speed deviation, in other words, so as to bring the radial speed of the magnetic head 22 closer to the target speed. In one example, the VCM controller 102 calculates the VCM current command value so that the greater the absolute value of the speed deviation, the greater the VCM current command value.

[0060] Adder 113 corrects the VCM current indication value by adding the correction amount for feedforward control to the VCM current indication value obtained by VCM controller 102. The VCM current indication value before correction by adder 113 is referred to as a first VCM current indication value. The VCM current indication value before correction by adder 113 is referred to as a second VCM current indication value.

[0061] The VCM current indication value used by the head velocity estimator 109 to estimate the velocity of the magnetic head 22 is the first VCM current indication value.

[0062] The VCM driver 103 generates a VCM current of an amount corresponding to the second VCM current instruction value. The VCM current generated by the VCM driver 103 is supplied to the VCM 16 in the control target Ctgt.

[0063] The VCM current detector 104 detects the amount of the VCM current generated by the VCM driver 103 and supplied to the VCM 16. The amount of the VCM current detected by the VCM current detector 104 is recorded as a VCM current detection value.

[0064] The first FF controller 30 calculates a correction amount for feedforward control based on the detection value of the first vibration sensor 17a. The second FF controller 30 calculates a correction amount for feedforward control based on the detection value of the second vibration sensor 17b. The third FF controller 30 calculates a correction amount for feedforward control based on the VCM current detection value.

[0065] Adder 114 sums the correction amounts obtained by first FF controller 30, second FF controller 30, and third FF controller 30. The sum of the correction amounts obtained by adder 114 is input to adder 113. Adder 113 adds the sum of the correction amounts input from adder 114 to the first VCM current indication value to obtain a second VCM current indication value.

[0066] Furthermore, the first vibration sensor 17a, the second vibration sensor 17b, and the VCM current detector 104 are each an example of a second sensor. One of the first vibration sensor 17a, the second vibration sensor 17b, and the VCM current detector 104 is an example of a first sensor that detects a predetermined physical quantity. The physical quantity detected by the first vibration sensor 17a and the second vibration sensor 17b is vibration. The physical quantity detected by the VCM current detector 104 is the VCM current.

[0067] The correction amounts obtained by the first, second, and third FF controllers 30 are calculated using an IIR (Infinite Impulse Response) filter. That is, the first, second, and third FF controllers 30 each have an IIR transfer function.

[0068] Because IIR filters have internal feedback, they can achieve complex control with a simple structure compared to FIR (Finite Impulse Response) filters. When attempting to use an FIR filter to perform control equivalent to that of an IIR filter, the order of the FIR filter inevitably increases, which in turn increases the amount of calculation required for the FIR filter. Here, by using IIR filters to calculate the correction values ​​for each of the first, second, and third FF controllers 30, highly accurate feedforward control can be achieved with minimal calculations.

[0069] The FF controller adjustment mechanism 105 independently adjusts the coefficients of the transfer function of the IIR filter used in the first FF controller 30, the coefficients of the transfer function of the IIR filter used in the second FF controller 30, and the coefficients of the transfer function of the IIR filter used in the third FF controller 30. The FF controller adjustment mechanism 105 simultaneously adjusts the coefficients of the numerator and the denominator of the transfer function of each IIR filter.

[0070] The stability determination unit 110 determines whether a seek stabilization operation is being performed based on the position deviation. During the seek stabilization operation, a signal indicating that the seek stabilization operation is being performed is input to the FF controller adjustment unit 105. The signal indicating whether the seek stabilization operation is being performed is recorded as a stability flag.

[0071] The change in the amount of position deviation during the seek stabilization operation is related to the accuracy of positioning control. When the accuracy of positioning control deteriorates due to interference (here, vibration or fluctuations in VCM current), the amplitude of the position deviation increases, or the time required for the seek stabilization operation becomes longer, compared to the case where the positioning control accuracy is good. In other words, the change in the amount of position deviation during the seek stabilization operation can be considered to reflect the influence of interference. Therefore, the stability determination unit 110 adjusts the coefficients of the transfer function of the IIR filter of each of the first FF controller 30, the second FF controller 30, and the third FF controller 30 based on the change in the amount of position deviation during the seek stabilization operation.

[0072] In addition to the stability flag, the position deviation amount, the detection value of the first vibration sensor 17a, the detection value of the second vibration sensor 17b, and the VCM current detection value are input to the FF controller adjustment mechanism 105. Based on this input information, the FF controller adjustment mechanism 105 adjusts the coefficients of the transfer function of the IIR filter of each of the first FF controller 30, the second FF controller 30, and the third FF controller 30.

[0073] The timing for adjusting the transfer function coefficients of each IIR filter is not limited to a specific timing. The controller 30 may adjust the transfer function coefficients of each IIR filter periodically or upon occurrence of a specific event.

[0074] Here, as an example, it is assumed that when the positioning accuracy fails to meet a predetermined benchmark, the coefficients of the transfer functions of each IIR filter are adjusted. More specifically, the controller 30 monitors IOPS (Input / Output Operations per Second). IOPS is the number of processing operations per unit time performed by the disk device 1 and is one of the indicators representing the performance of the disk device 1. When IOPS becomes smaller than a predetermined threshold (denoted as threshold Th1), the coefficients of the transfer functions of each IIR filter are adjusted by the FF controller adjustment mechanism 105. It can be considered that in response to the deterioration of positioning accuracy, seek errors increase and IOPS decreases. Therefore, when IOPS becomes smaller than the threshold Th1 pre-set as a benchmark value, the controller 30 restores the positioning accuracy by adjusting the coefficients of the transfer functions of each IIR filter.

[0075] Figure 4 This is a flowchart showing an example of the operation of the magnetic disk device 1 according to the embodiment.

[0076] The controller 30 determines whether IPOS is smaller than a threshold value Th1 ( S101 ).

[0077] When IPOS is not smaller than the threshold value Th1 ( S101 : NO), the control proceeds to S114 described later.

[0078] When IPOS is smaller than the threshold value Th1 (S101: YES), the controller 30 adjusts the coefficients of the transfer functions of the respective IIR filters through the operations of S102 to S113. The operations of S102 to S113 are an example of the first operation.

[0079] In the first operation, the controller 30 first determines whether the execution timing of the seek operation has arrived (S102). If the execution timing of the seek operation has not arrived (S102: No), the controller 30 executes the process of S102 again.

[0080] When the seek operation execution timing arrives (S102: YES), the FF controller adjustment mechanism 105 disables the feedforward control function of the first, second, and third FF controllers 30 (S103). In S103, the FF controller adjustment mechanism 105 causes the first, second, and third FF controllers 30, 30, 30 to output, for example, 0 as a correction value. As a result, the first, second, and third FF controllers 30, 30, 30, are no longer performing feedforward control and begin positioning control under the influence of disturbances such as vibration and VCM current fluctuations.

[0081] The FF controller adjustment mechanism 105 starts acquiring the first vibration detection value, the second vibration detection value, the VCM current detection value, and the position deviation amount ( S104 ). Then, the controller 30 starts a seek operation ( S105 ).

[0082] Furthermore, the detection position is acquired from each servo sector in synchronization with the rotation angle of the magnetic disk 11. The controller 30 forms a sampling value control system that determines the input to the control object (e.g., VCM 16) at a fixed time interval. The VCM 16 can be driven at a 1 / N cycle (N is an integer greater than or equal to 2) of the detection position acquisition cycle. However, the acquisition timing of the first vibration detection value, the second vibration detection value, the VCM current detection value, and the position deviation amount is set to be the same as the acquisition timing of the detection position. During the seek operation, the time transition of each of the first vibration detection value, the second vibration detection value, the VCM current detection value, and the position deviation amount is acquired as a respective waveform.

[0083] When the seek operation is completed ( S106 ), the FF controller adjustment mechanism 105 ends obtaining the first vibration detection value, the second vibration detection value, the VCM current detection value, and the position deviation amount ( S107 ).

[0084] The FF controller adjustment mechanism 105 obtains a waveform during the seek stabilization operation from the waveform of the position deviation amount obtained during the seek operation ( S108 ).

[0085] During the seek stabilization operation, the stability flag is maintained in an active (ON) state by the stability determination unit 110. Based on the stability flag, the FF controller adjustment unit 105 identifies and obtains the waveform during the seek stabilization operation from the position deviation waveform. The waveform of the position deviation during the seek stabilization operation obtained by the process of S108 is recorded as the stable position waveform.

[0086] Figure 5 This figure shows examples of various waveforms obtained in the magnetic disk device 1 of the embodiment. The figure shows the waveforms of the position deviation amount, VCM current detection value, first vibration detection value, second vibration detection value, and stability flag from the start of the seek operation to the completion of the seek operation.

[0087] When the seek operation begins, an acceleration period begins, in which the magnetic head 22 is greatly accelerated toward the target track. Then, as the magnetic head 22 approaches the target track, a deceleration period begins, in which the magnetic head 22 is greatly decelerated. When the position deviation amount becomes less than a predetermined value after the deceleration period, a seek stabilization operation is performed. By maintaining the stability flag active, the FF controller adjustment mechanism 105 is notified that the seek stabilization operation is in progress. Regarding the position deviation amount, the FF controller adjustment mechanism 105 obtains a waveform during the seek stabilization operation.

[0088] Regarding the VCM current detection value, the first vibration detection value, and the second vibration detection value, waveforms are acquired during a period from the start of the seek operation to the completion of the seek operation (in other words, the seek stabilization operation).

[0089] The stable position waveform is an example of the first waveform. The waveform of the first vibration detection value, the waveform of the second vibration detection value, and the waveform of the VCM current detection value are each an example of the second waveform.

[0090] Return the instructions to Figure 4 .

[0091] Following the process of S108 , the FF controller adjustment mechanism 105 performs frequency analysis on the waveform of the first vibration detection value, the waveform of the second vibration detection value, the waveform of the VCM current detection value, and the stable position waveform ( S109 ).

[0092] Frequency analysis is analysis using, for example, discrete Fourier transform. The FF controller adjustment unit 105 obtains, for each waveform, a first characteristic representing the relationship between frequency and amplitude (represented as gain) and a second characteristic representing the relationship between frequency and phase through frequency analysis.

[0093] The FF controller adjustment unit 105 specifies a frequency band in which the gain of the stable position waveform is larger than the threshold value Th2 based on the first characteristic related to the stable position waveform ( S110 ).

[0094] The reference value used to determine whether correction by feedforward control is necessary is pre-set as threshold Th2. Specifically, frequency bands where the gain is greater than threshold Th2 are considered to require correction of the VCM current indicated value by feedforward control, while frequency bands where the gain is not less than threshold Th2 are considered to not require correction by feedforward control. In S110, the frequency bands requiring correction by feedforward control are determined. The frequency bands obtained by the process in S110 are referred to as target frequency bands.

[0095] The target frequency band is an example of the first frequency band, and frequency bands other than the target frequency band are examples of the second frequency band.

[0096] The FF controller adjustment unit 105 obtains coherence in a target frequency band between the waveforms of each of the first vibration detection value, the second vibration detection value, and the VCM current detection value and the stable position waveform ( S111 ).

[0097] Then, the FF controller adjustment mechanism 105 determines a physical quantity in which the coherence of the vibration detected by the first vibration sensor 17a, the vibration detected by the second vibration sensor 17b, and the VCM current detected by the VCM current detector 104 in the target frequency band is greater than the threshold value Th3 (S112).

[0098] In S112, interference that degrades positioning control is determined. A threshold value Th3 is pre-set as the reference value for determining whether the physical quantity detected by each sensor is interference that degrades positioning control. Physical quantities with a coherence greater than Th3 are considered interference that degrades positioning control, while physical quantities with a coherence less than Th3 are not considered interference that degrades positioning control. The physical quantity determined by the process in S112 is referred to as the target physical quantity.

[0099] The FF controller adjustment mechanism 105 adjusts the coefficients of the transfer functions of the FF controllers that perform feedforward control based on the target physical quantity in the first FF controller 30, the second FF controller 30, and the third FF controller 30 (S113). In S113, the coefficients of the numerator and the denominator of the IIR transfer functions of the FF controllers that perform feedforward control based on the target physical quantity are adjusted simultaneously.

[0100] Figure 6These diagrams illustrate an example of a method for adjusting the coefficients of the numerator and denominator of an IIR-type transfer function of an FF controller according to an embodiment. Part (A) is a graph showing the first characteristic, and part (B) is a graph showing the second characteristic. The graphs in part (A) and (B) respectively show the frequency characteristic of the target physical quantity and the target frequency characteristic (hereinafter referred to as the target frequency characteristic) of the FF controller for performing feedforward control based on the target physical quantity.

[0101] As shown in parts (A) and (B), the FF controller adjustment mechanism 105 designs the target frequency characteristics so as to suppress the target physical quantity in frequency bands other than the target frequency band and pass the target physical quantity in the target frequency band.

[0102] The FF controller adjustment mechanism 105 calculates the coefficients of the numerator and denominator of the FF controller's transfer function so that the frequency characteristics of the FF controller's transfer function are consistent with or close to the target frequency characteristics. The calculation algorithm for calculating the coefficients of the numerator and denominator of the transfer function to achieve the target frequency characteristics is not limited to a specific algorithm. The FF controller adjustment mechanism 105 calculates the coefficients of the numerator and denominator of the FF controller's transfer function based on any known calculation algorithm.

[0103] Return the instructions to Figure 4 .

[0104] After the processing of S113, when the seek operation is performed, the FF controller adjustment mechanism 105 turns on the feedforward control function of the first FF controller 30, the second FF controller 30, and the third FF controller 30 (S114). Then, the control returns to S101.

[0105] In the example described above, magnetic disk drive 1 includes three sensors for detecting physical quantities that may cause interference: first vibration sensor 17a, second vibration sensor 17b, and VCM current detector 104. The number of sensors for detecting physical quantities that may cause interference included in magnetic disk drive 1 is not limited to a specific number and may be one or more.

[0106] The number of FF controllers included in the controller 30 is not limited to 3. The controller 30 includes the same number of FF controllers as the number of sensors for detecting physical quantities that may become disturbances, and each FF controller performs feedforward control based on the physical quantity detected by the respective sensor.

[0107] In addition, if Figure 4As shown in S112 and S113 of FIG. 1 , the controller 30 determines the FF controller of the three FF controllers (first FF controller 106, second FF controller 107, and third FF controller 108) to be the target for adjustment of the transfer function coefficients based on the coherence in the target frequency band. The method for determining the FF controller to be the target for adjustment of the transfer function coefficients is not limited to this. The controller 30 may also determine that all three FF controllers are the targets for adjustment of the transfer function coefficients.

[0108] As described above, according to the embodiment, the controller 30 generates the first VCM current indication value by reducing the position deviation through the target speed table 101 and the VCM controller 102. Furthermore, the controller 30 corrects the first VCM current indication value through feedforward control based on the physical quantity detected by the sensor, and inputs the second VCM current indication value, which is the corrected first VCM current indication value, to the motor driver IC 21. The motor driver IC 21 generates a VCM current of an amount corresponding to the second VCM current indication value through the VCM driver 103, and supplies the generated VCM current to the VCM 16. The controller 30 performs the first action (for example, referring to Figure 4 In the first operation, controller 30 obtains a position deviation waveform and defines a frequency band where the position deviation waveform exceeds threshold value Th2 as a target frequency band. Controller 30 then adjusts the coefficients of the feedforward control transfer function so that the sensor detection value is suppressed in frequency bands outside the target frequency band and a correction to the first VCM current indication value is output based on the target frequency band.

[0109] The controller 30 can autonomously adjust the coefficients of the transfer function of the feedforward control, thereby improving positioning accuracy.

[0110] Furthermore, according to the embodiment, magnetic disk drive 1 includes multiple sensors for detecting physical quantities, and controller 30 corrects the first VCM current indication value using multiple feedforward controls based on the physical quantities detected by the different sensors. In a first operation, controller 30 selects one or more of the multiple feedforward controls as targets for adjustment of the transfer function coefficients.

[0111] This can improve positioning accuracy.

[0112] In addition, according to the embodiment, the controller 30 obtains a plurality of waveforms from a plurality of sensors. The controller 30 obtains the coherence of each of the plurality of waveforms obtained from the plurality of sensors with the waveform of the position deviation amount at the target frequency band. Then, a feedforward control based on a physical quantity having a coherence greater than a threshold value Th3 is determined among the plurality of feedforward controls, and the coefficient of the transfer function of the determined feedforward control is adjusted (for example, referring to Figure 4S112 and S113).

[0113] Specifically, the physical quantity that is a disturbance causing deterioration in positioning control is identified among multiple physical quantities detected by multiple sensors, and the coefficient of the transfer function of the feedforward control based on the identified physical quantity is adjusted. This improves positioning accuracy.

[0114] Furthermore, according to the embodiment, the controller 30 acquires waveforms of each of the plurality of sensors during the seek operation, and acquires a waveform of the positional deviation amount during the seek stabilization operation.

[0115] This improves the positioning accuracy of the seek operation and improves the performance of the magnetic disk device 1 .

[0116] Furthermore, the first operation may be performed during a tracking operation in addition to or instead of a seek operation. For example, the controller 30 may acquire waveforms from multiple sensors and waveforms indicating positional deviation during part or all of the tracking operation. The controller 30 may then use these acquired waveforms to determine a target frequency band, determine feedforward control of the target based on adjustment of the coefficients of the transfer function for coherence in the target frequency band, and so on.

[0117] According to the embodiment, the controller 30 monitors the number of processes per unit time of the magnetic disk device 1 and executes the first action (for example, referring to Figure 4 S101).

[0118] Therefore, when the performance is degraded, the performance can be restored by adjusting the coefficients of the transfer function.

[0119] Furthermore, according to the embodiment, each FF controller has an IIR transfer function, and the controller 30 adjusts the coefficients included in the numerator of the transfer function and the coefficients included in the denominator of the transfer function.

[0120] Compared to FIR filters, IIR filters can achieve complex control with a simple structure. Each FF controller is corrected using IIR filter calculations, enabling highly accurate feedforward control with minimal computational effort. Furthermore, controller 30 adjusts the coefficients included in the numerator and denominator of the transfer function, enabling the transfer function of the FF controller to have a frequency characteristic that is as close as possible to the target frequency characteristic. This means that the target frequency characteristic can be achieved simply and with high precision.

[0121] Furthermore, the transfer function of each FF controller may not be an IIR transfer function, but may be an FIR transfer function for some or all of the FF controllers.

[0122] While several embodiments of the present invention have been described, these embodiments are provided as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other ways, and various omissions, substitutions, and modifications may be made without departing from the gist of the invention. These embodiments and their variations are within the scope and gist of the invention and are within the scope of the invention set forth in the claims and their equivalents.

Claims

1. A magnetic disk device comprising: disk; A magnetic head, for writing data to and reading data from the magnetic disk; an actuator arm having the magnetic head disposed at its front end; a motor for moving the magnetic head in a radial direction of the magnetic disk by moving the actuator arm; a drive circuit that generates a first current corresponding to the instruction value for driving the motor and supplies the generated first current to the motor; A first sensor detects a predetermined physical quantity; as well as controller, the controller, detecting the position of the magnetic head, generating a first indication value so as to reduce the amount of deviation of the detection position of the magnetic head from the target position of the magnetic head; The first indication value is corrected by a first feedforward control based on a first detection value of the first sensor. inputting a second instruction value, which is the corrected first instruction value, into the driving circuit as the instruction value, The first action is executed when the set event occurs. The first action is the following action: obtaining a first waveform as a waveform of the deviation amount, obtaining a first frequency band as a frequency band having an amplitude greater than a first threshold value from the first waveform, and adjusting the coefficient of the transfer function of the first feedforward control in such a manner that the first detection value is suppressed at a second frequency band different from the first frequency band and a correction amount for the first indication value is output based on the first detection value at the first frequency band.

2. The magnetic disk device according to claim 1, further comprising a plurality of second sensors each detecting a predetermined physical quantity, wherein the plurality of second sensors include the first sensor; The controller corrects the first indication value through a plurality of second feedforward controls, the plurality of second feedforward controls including the first feedforward control, the plurality of second feedforward controls each generating a correction amount for the first indication value based on a second detection value of a different second sensor among the plurality of second sensors. In the first action, the controller adjusts the coefficient of the transfer function of each of one or more of the multiple second feedforward controls in such a manner that the second detection value is suppressed at the second frequency band and a correction amount for the first indication value is generated based on the second detection value at the first frequency band.

3. The magnetic disk device according to claim 2, In the first action, the controller acquiring a plurality of second waveforms, each of which is a waveform of a second detection value from each of the plurality of second sensors; obtaining coherence between each of the plurality of second waveforms and the first waveform in the first frequency band, determining a second feedforward control based on a second detection value constituting the second waveform having the coherence greater than a second threshold value among the plurality of second feedforward controls, The coefficient of the determined transfer function of the second feedforward control is adjusted.

4. The magnetic disk device according to claim 3, The plurality of second waveforms are waveforms during the seek operation, The first waveform is a waveform during a seek stabilization operation.

5. The magnetic disk device according to claim 1, The transfer function is an IIR type transfer function in which the numerator and denominator each contain coefficients. The IIR type refers to an infinite impulse response type. In the first operation, the controller adjusts the coefficient included in the numerator of the transfer function and the coefficient included in the denominator of the transfer function.

6. The magnetic disk device according to any one of claims 2 to 4, The transfer functions of the plurality of second feedforward controls are each an IIR type transfer function whose numerator and denominator each include coefficients, and the IIR type refers to an infinite impulse response type. In the first operation, the controller adjusts the coefficients included in the numerator and the denominator.

7. The magnetic disk device according to claim 1, The first sensor is a vibration sensor or a sensor that detects the amount of the first current supplied to the motor.

8. The magnetic disk device according to any one of claims 2 to 4, The plurality of second sensors include a vibration sensor and a sensor that detects an amount of the first current supplied to the motor.

9. The magnetic disk device according to any one of claims 1 to 4, The controller monitors the number of transactions per unit time of the magnetic disk device. The set event is that the number of processes is less than a third threshold.

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