Magnetic disk device

Abstract

To provide a magnetic disk device with high performance.SOLUTION: In a magnetic disk device, a current detection circuit detects the amount of a first current for driving a motor generated by a drive circuit. A controller acquires an instruction value based on the deviation of the amount of the first current detected by the current detection circuit from the instruction value during a seek operation. Then, the controller inputs the acquired instruction value to the drive circuit.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This embodiment relates to a magnetic disk device. [Background technology]

[0002] In a magnetic disk drive, a voice coil motor (VCM) moves the magnetic head radially across the magnetic disk. During a seek operation, the more current supplied to the VCM, the faster the magnetic head moves, shortening the time required for the seek operation. In other words, performance improves.

[0003] However, if there is insufficient margin between the supply voltage and the voltage drop across the VCM caused by supplying current to the VCM, the intended amount of current cannot be supplied to the VCM, which can result in a seek operation failure, which in turn can result in a deterioration in performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 6,781,787 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment is to provide a high-performance magnetic disk drive. [Means for solving the problem]

[0006] According to one embodiment, a magnetic disk drive includes a magnetic disk, an arm, a motor, a drive circuit, a current detection circuit, and a controller. The arm is provided with a magnetic head that accesses the magnetic disk. The motor moves the arm to move the magnetic head in the radial direction of the magnetic disk. The drive circuit generates a first current that drives the motor in an amount corresponding to an instruction value, and supplies the generated first current to the motor. The current detection circuit detects the amount of the first current generated by the drive circuit. During a seek operation, the controller obtains an instruction value for moving the radial position of the magnetic head closer to a target position based on the deviation of the amount of the first current detected by the current detection circuit from the instruction value. The controller then inputs the obtained instruction value to the drive circuit. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating an example of a hardware configuration of a magnetic disk device according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a control block for a seek operation provided in the magnetic disk device according to the embodiment. [Figure 3] FIG. 3 is a flowchart illustrating a seek operation of the magnetic disk device according to the embodiment. [Figure 4] FIG. 4 is a flowchart illustrating an example of an operation of updating the speed adjustment coefficient by the seek speed adjuster according to the embodiment. [Figure 5] FIG. 5 is a graph showing an example of a distribution of instantaneous values ​​of the seek voltage margin estimated by the seek voltage margin estimator according to the embodiment. [Figure 6] FIG. 6 is a graph showing an example of a distribution of VCM current deviation amounts according to the embodiment. [Figure 7] FIG. 7 is a diagram illustrating an example of the results of the operation of the magnetic disk device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A magnetic disk drive according to an embodiment will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to this embodiment.

[0009] (Embodiment) FIG. 1 is a diagram illustrating an example of a hardware configuration of a magnetic disk device 1000 according to an embodiment.

[0010] The magnetic disk device 1000 is connected to a host (not shown). The magnetic disk device 1000 can receive access commands from the host. The access commands include write commands and read commands.

[0011] The magnetic disk device 1000 includes a magnetic disk 1 having a magnetic layer formed on its surface. The magnetic disk device 1000 accesses the magnetic disk 1 in response to an access command. The access includes writing data and reading data.

[0012] The magnetic disk 1 is rotated at a predetermined angular velocity by a spindle motor (not shown). The magnetic head 2 accesses the magnetic disk 1 by means of a write head and a read head provided thereon.

[0013] 1 shows one magnetic disk 1. However, the magnetic disk device 1000 may include multiple magnetic disks 1. When the magnetic disk device 1000 includes multiple magnetic disks 1, the multiple magnetic disks 1 are rotated together by a spindle motor. In addition, a magnetic head 2 is provided for each recording surface of the multiple magnetic disks 1.

[0014] In addition to the magnetic disk 1 and the magnetic head 2, the magnetic disk device 1000 includes an arm 3, a VCM 4, a signal processing circuit 9, a position detection circuit 10, a controller 13, a VCM drive circuit 14, a VCM current detection circuit 15, an A / D (Analog-to-Digital) conversion circuit 16, a power supply voltage detection circuit 17, and an A / D conversion circuit 18.

[0015] The magnetic head 2 is provided at the tip of an arm 3. When the arm 3 is moved by a VCM 4, the magnetic head 2 is moved in the radial direction of the magnetic disk 1.

[0016] Servo information is written to a magnetic layer formed on the surface of the magnetic disk 1 by, for example, a servo writer. The servo information may be written to the magnetic disk 1 by self-servo writing (SSW). The servo information is information used to obtain the current position of the magnetic head 2. The servo information may include sector / cylinder information, a burst pattern, and a postcode.

[0017] 1 shows radially arranged servo areas 7 as an example of the arrangement of servo areas in which servo information is written. Between the servo areas 7, data areas 8 are provided in which data (e.g., data received from a host) can be written. One servo area 7 and the data area 8 through which the magnetic head 2 passes immediately after the servo area 7 constitute a servo sector 6.

[0018] When the magnetic head 2 passes over the servo area 7, servo information is read from the servo area 7, and the current position of the magnetic head 2 is detected based on the read servo information. As the magnetic disk 1 is rotated at a constant angular velocity, the magnetic head 2 passes over the servo area 7 at regular time intervals. Therefore, the current position of the magnetic head 2 is detected at regular time intervals.

[0019] A plurality of concentric tracks 5 are provided at a predetermined pitch in the radial direction of the magnetic disk 1. A large number of sectors are formed along each track 5 in each data area 8. Data is written to and read from each sector by the magnetic head 2.

[0020] The signal processing circuit 9 demodulates the signal read by the magnetic head 2. The signal processing circuit 9 can also perform error correction when demodulating the signal.

[0021] The position detection circuit 10 separates data and position information (i.e., the demodulation result of servo information) from the signal demodulated by the signal processing circuit 9. The position detection circuit 10 detects the current position of the magnetic head 2 from the position information. The current position of the magnetic head 2 detected by the position detection circuit 10 is referred to as the position detection value.

[0022] The controller 13 performs overall control of the magnetic disk device 1000, including positioning control of the magnetic head 2. The controller 13 includes a CPU (Central Processing Unit) 11, which is a processor capable of executing computer programs, and a ROM (Read Only Memory) 12, which is a non-volatile storage device. A firmware program is stored in the ROM 12. The CPU 11 controls the magnetic disk device 1000 based on the firmware program stored in the ROM 12.

[0023] The positioning control includes control of a seek operation and control of a tracking operation. The seek operation is an operation of moving the magnetic head 2 in the radial direction toward the target track 5. The tracking operation is an operation of maintaining the magnetic head 2 on the target track 5.

[0024] In positioning control, the controller 13 (more precisely, the CPU 11) calculates a command value for the amount of current to drive the VCM 4 based on the position detection value acquired by the position detection circuit 10 so that the radial position of the magnetic head 2 approaches the target position. Hereinafter, the current that drives the VCM 4 will be referred to as the VCM current. The command value for the amount of VCM 4 current will be referred to as the VCM current command value.

[0025] The VCM drive circuit 14 generates a VCM current of an amount corresponding to the VCM current command value, and supplies the generated VCM current to the VCM 4.

[0026] VCM current detection circuit 15 detects the amount of VCM current generated by VCM drive circuit 14 and supplied to VCM 4. The amount of VCM current detected by VCM drive circuit 14 is converted into a digital value by A / D conversion circuit 16 and input to CPU 11. Hereinafter, the amount of VCM current detected by VCM drive circuit 14 and converted into a digital value by A / D conversion circuit 16 will be referred to as the actual VCM current value.

[0027] The power supply voltage detection circuit 17 is a circuit that detects the power supply voltage, i.e., the voltage of the power supplied from outside to the magnetic disk device 1000. The voltage value detected by the power supply voltage detection circuit 17 is converted into a digital value by the A / D conversion circuit 18, and the converted digital voltage value is input to the CPU 11. Hereinafter, the voltage value detected by the power supply voltage detection circuit 17 and converted into a digital value by the A / D conversion circuit 18 will be referred to as the power supply voltage value.

[0028] The position detection values ​​are acquired from each servo area 7 in synchronization with the rotation angle of the magnetic disk 1. The controller 13 constitutes a sampled value control system that determines the input to a controlled object (for example, the VCM 4) at regular time intervals. The VCM 4 can be driven at a cycle that is 1 / Nth of the cycle of acquiring the position detection values ​​(N is an integer equal to or greater than 2), allowing for multi-rate control. However, the timing for acquiring the actual VCM current value and the power supply voltage detection value is set to be the same as the timing for acquiring the position detection values.

[0029] During a seek operation, the greater the VCM current, the faster the magnetic head 2 moves (more precisely, the radial movement speed of the magnetic head 2), thereby improving performance. However, the amount of voltage drop in the VCM 4 (hereinafter referred to as the seek voltage) increases depending on the amount of VCM current, etc. If the margin between the seek voltage and the power supply voltage (hereinafter referred to as the seek voltage margin) is insufficient, the intended amount of current cannot be passed to the VCM 4, especially when the magnetic head 2 is decelerating, which can result in a failed seek operation and a deterioration in performance. Therefore, it is desirable to maintain the seek voltage margin small enough so that it does not become insufficient.

[0030] Therefore, the CPU 11 estimates the seek voltage margin and controls the amount of VCM current so that the estimated value of the seek voltage margin is maintained within a predetermined range.

[0031] The instantaneous value of the seek voltage margin obtained by estimation is not sufficiently accurate and has large variations. Therefore, the CPU 11 obtains the seek voltage margin used to control the amount of VCM current by averaging the seek voltage margins obtained by multiple seek operations.

[0032] However, control using only the average seek voltage margin obtained by multiple seek operations cannot accurately respond to instantaneous changes in the actual seek voltage margin, and the actual seek voltage margin may temporarily become insufficient, resulting in frequent seek operation failures.

[0033] Therefore, in this embodiment, the CPU 11 controls the VCM current during a seek operation not only using the estimated seek voltage margin, but also using the difference (hereinafter referred to as the VCM current deviation) obtained by subtracting the actual VCM current value from the VCM current command value. If the seek voltage margin is insufficient, the VCM current deviation increases. Because the actual VCM current value can be obtained accurately in real time, the CPU 11 can accurately detect signs of a seek voltage margin deficiency or the actual seek voltage margin deficiency in real time.

[0034] By using the VCM current deviation, the CPU 11 can precisely control the VCM current to detect signs of or prevent a seek voltage margin shortage, thereby maintaining the actual seek voltage margin at a small enough level to avoid a shortage, resulting in improved performance compared to when only the average seek voltage margin is used.

[0035] FIG. 2 is a diagram illustrating an example of a control block for a seek operation provided in the magnetic disk device 1000 according to the embodiment.

[0036] The magnetic disk device 1000 includes a target speed table 101, a seek speed adjuster 102, a VCM controller 103, a VCM driver 104, a VCM actual current detector 105, a VCM resistance estimator 106, a power supply voltage detector 107, a seek voltage margin estimator 108, a head speed estimator 109, a seek error determiner 110, a seek settling determiner 111, and three subtractors 112 to 114.

[0037] The target speed table 101 is stored in, for example, the ROM 12 and is read by the CPU 11. The seek speed adjuster 102, VCM controller 103, VCM resistance estimator 106, seek voltage margin estimator 108, head speed estimator 109, seek error determiner 110, seek settling determiner 111, and three subtractors 112 to 114 are realized by the CPU 11. The VCM driver 104 corresponds to the VCM drive circuit 14. The VCM actual current detector 105 corresponds to the VCM current detection circuit 15 and the A / D conversion circuit 16. The power supply voltage detector 107 corresponds to the power supply voltage detection circuit 17 and the A / D conversion circuit 18.

[0038] The magnetic disk device 1000 controls the control object Ctgt using these functional components. The control object Ctgt includes the VCM 4, the arm 3, the magnetic head 2, a signal processing circuit 9, and a position detection circuit 10. As a result of controlling the control object Ctgt, the position detection circuit 10 outputs a position detection value that is a detection value of the current radial position of the magnetic head 2.

[0039] The CPU 11 obtains a target position Ptgt, which is a target position in the radial direction, through a predetermined calculation. The subtractor 112 calculates the difference between the target position Ptgt in the radial direction and the position detection value by subtracting the position detection value from the target position Ptgt. The difference between the target position Ptgt in the radial direction and the position detection value is referred to as the position deviation amount.

[0040] The CPU 11 acquires the first target speed based on the position deviation amount and the target speed table 101.

[0041] The target speed table 101 is information that defines the relationship between the seek distance and the radial target speed of the magnetic head 2. The seek distance is the radial distance from the current position of the magnetic head 2 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 2 is defined so that, for example, the longer the seek distance, the faster the target speed of the magnetic head 2. The CPU 11 searches the target speed table 101 using the position deviation amount as the seek distance, and obtains the target speed of the magnetic head 2 corresponding to the position deviation amount as the first target speed.

[0042] The target speed table 101 may be information in a table format or may be configured as a mathematical formula.

[0043] The speed of the magnetic head 2 can be easily converted into the speed of the VCM 4, and vice versa. Therefore, the target speed may be expressed as the speed of the VCM 4. Hereinafter, unless otherwise specified, the speed (including the target speed) will be described as representing the speed of the magnetic head 2.

[0044] The seek speed adjuster 102 obtains the second target speed by performing a calculation using the first target speed and a parameter value. More specifically, the seek speed adjuster 102 obtains the second target speed by multiplying the first target speed by a coefficient managed as a parameter value. This coefficient is referred to as a speed adjustment coefficient.

[0045] The seek speed adjuster 102 also updates a speed adjustment coefficient, which is a parameter value, based on at least the VCM current deviation. As an example, the seek speed adjuster 102 updates the speed adjustment coefficient based on an estimated seek voltage margin, a seek settling evaluation value, whether a seek error has occurred, and the VCM current deviation. By changing the speed adjustment coefficient through updating, the direction and amount of change from the first target speed to the second target speed are adjusted. For example, if the speed adjustment coefficient is greater than 1, the second target speed is made faster than the first target speed. If the speed adjustment coefficient is less than 1, the second target speed is made slower than the first target speed.

[0046] A seek error is a failure of a seek operation. Whether or not a seek error has occurred is determined by the seek error determiner 110. The seek error determiner 110 determines whether or not the seek operation has failed based on the time required for the seek operation, the amount of positional deviation, the amount of overshoot by which the magnetic head 2 passes over the target position Ptgt, and the like.

[0047] At the end of the seek operation, a seek settling operation is executed. The seek settling operation is an operation that determines whether or not it is OK to start accessing the magnetic disk 1 based on the amount of positional deviation. In one example, the seek settling operation determines whether or not the amount of positional deviation has remained within a set range for a predetermined period of time. When it is confirmed that the amount of positional deviation has remained within the set range for a predetermined period of time, the seek settling operation (and the seek operation) is completed.

[0048] In the following description, the amount of position deviation during the seek and settling operation may be referred to as a position error.

[0049] The seek settling determinator 111 acquires a seek settling evaluation value. The seek settling evaluation value is, for example, the maximum absolute value of the position error during a set period (e.g., a period of a predetermined number of samplings) immediately after the completion of the seek settling operation (in other words, the seek operation). Even if the seek settling operation is completed, if the speed of the magnetic head 2 during the seek operation is too fast, the position error may become large after the seek settling operation. A large position error after the seek settling operation is undesirable from the viewpoint of the accuracy of subsequent positioning control (e.g., tracking operation). Therefore, the seek settling determinator 111 acquires the sheet settling evaluation value described above so that the position error can be evaluated after the seek settling operation. The seek speed adjuster 102 uses the sheet settling evaluation value to update the speed adjustment coefficient, thereby suppressing the adverse effect of the second target speed on the position error after the seek settling operation.

[0050] The head speed estimator 109 estimates the speed of the magnetic head 2 based on the position deviation amount and the VCM current command value.

[0051] The subtractor 113 obtains the velocity deviation amount by subtracting the estimated value of the velocity of the magnetic head 2 obtained by the head velocity estimator 109 from the second target velocity.

[0052] The VCM controller 103 calculates a VCM current command value based on the velocity deviation. The VCM controller 103 calculates the VCM current command value so that the velocity deviation becomes smaller, in other words, so that the radial velocity of the magnetic head 2 approaches the second target velocity. In one example, the VCM controller 103 calculates the VCM current command value so that the VCM current command value becomes larger as the absolute value of the velocity deviation becomes larger.

[0053] The VCM driver 104 generates a VCM current of an amount corresponding to the VCM current command value. The VCM current generated by the VCM driver 104 is supplied to VCM4 of the control target Ctgt.

[0054] The VCM actual current detector 105 detects the amount of VCM current generated by the VCM driver 104 and supplied to the VCM 4. That is, the VCM actual current detector 105 obtains the actual VCM current value through detection.

[0055] The subtractor 114 obtains the VCM current deviation amount by subtracting the VCM current actual value from the VCM current command value. The VCM current deviation amount is input to the seek speed adjuster 102.

[0056] VCM resistance estimator 106 estimates the resistance of VCM 4 based on the estimated value of the speed of magnetic head 2 and the actual value of the VCM current obtained by head speed estimator 109. VCM resistance estimator 106 uses a table or a function to obtain an estimated value of the resistance of VCM 4 from the estimated value of the speed of magnetic head 2 estimated by head speed estimator 109 and the actual value of the VCM current.

[0057] The power supply voltage detector 107 detects the power supply voltage.

[0058] The seek voltage margin estimator 108 estimates the seek voltage margin based on the power supply voltage value detected by the power supply voltage detector 107, the estimated value of the speed of the magnetic head 2 obtained by the head speed estimator 109, and the estimated value of the resistance of the VCM 4 obtained by the VCM resistance estimator 106. The seek voltage margin estimator 108 estimates the seek voltage margin by, for example, calculating the following equation (1). V m =V in -(R VCM *I VCM +K*v h ) ···(1)

[0059] In equation (1), V m is the seek voltage margin. V in is the power supply voltage, R VCM is the resistance of VCM4, I VCM is the current supplied to VCM4. his the speed of the magnetic head 2. K is a constant that is multiplied by the speed of the magnetic head 2 to obtain the back electromotive force.

[0060] Note that (R VCM *I VCM +K*v h ) corresponds to the seek voltage, i.e., the voltage drop in VCM4.

[0061] The seek voltage margin estimate obtained by the seek voltage margin estimator 108 is input to the seek speed adjuster 102 .

[0062] Next, the operation of the magnetic disk device 1000 according to the embodiment will be described.

[0063] 3 is a flowchart for explaining the seek operation of the magnetic disk device 1000 according to the embodiment. In this diagram, the operation executed when the magnetic head 2 passes through the servo area 7 during the seek operation is explained. In other words, the series of operations shown in this diagram is repeatedly executed during the seek operation.

[0064] When the magnetic head 2 passes over the servo area 7, the magnetic disk device 1000 detects the current position of the magnetic head 2 based on the servo information read by the magnetic head 2 (S101). Specifically, the servo information read by the magnetic head 2 is demodulated by the signal processing circuit 9. The position detection circuit 10 obtains a position detection value based on the demodulated servo information.

[0065] The subtractor 112 obtains the position deviation amount, which is the difference between the target position Ptgt and the position detection value, by performing a calculation to subtract the position detection value from the target position Ptgt (S102).

[0066] The CPU 11 refers to the target speed table 101 to obtain a target speed corresponding to the position deviation amount as a first target speed (S103).

[0067] The seek speed adjuster 102 obtains the second target speed by adjusting the first target speed (S104). In this example, the seek speed adjuster 102 obtains the second target speed by multiplying the first target speed by a speed adjustment coefficient.

[0068] The head speed estimator 109 estimates the speed of the magnetic head 2 (S105).

[0069] The subtractor 113 obtains a speed deviation amount, which is the difference between the second target speed and the speed of the magnetic head 2, by subtracting the estimated value of the speed of the magnetic head 2 from the second target speed (S106).

[0070] The VCM controller 103 calculates a VCM current command value based on the speed deviation amount (S107).

[0071] The VCM driver 104 generates a VCM current of an amount corresponding to the VCM current command value, and supplies the generated VCM current to the VCM 4 (S108).

[0072] The VCM actual current detector 105 detects the amount of VCM current supplied to the VCM 4, that is, the VCM current actual value (S109).

[0073] The VCM resistance estimator 106 estimates the resistance of the VCM 4 based on the estimated value of the speed of the magnetic head 2 obtained by the head speed estimator 109 and the actual VCM current value detected by the VCM actual current detector 105 (S110).

[0074] The power supply voltage detector 107 detects the power supply voltage (S111).

[0075] The seek voltage margin estimator 108 estimates a seek voltage margin based on the power supply voltage value detected by the power supply voltage detector 107, the estimated value of the speed of the magnetic head 2 obtained by the head speed estimator 109, and the estimated value of the resistance of the VCM 4 obtained by the VCM resistance estimator 106 (S112).

[0076] The subtractor 114 obtains the VCM current deviation amount by subtracting the VCM current actual value from the VCM current command value (S113).

[0077] The seek error determiner 110 executes a seek error determination, that is, a determination as to whether or not a seek error has occurred (S114).

[0078] The seek speed adjuster 102 executes a process to update the speed adjustment coefficient (S115). Then, the operation when the magnetic head 2 passes through the servo area 7 is completed. The next time the magnetic head 2 passes through the servo area 7, the series of operations from S101 are executed again.

[0079] FIG. 4 is a flowchart showing an example of an operation of updating the speed adjustment coefficient by the seek speed adjuster 102 according to the embodiment.

[0080] First, the seek speed adjuster 102 determines whether the absolute value of the VCM current deviation is greater than a threshold value Th1 (S201). The threshold value Th1 is a threshold value of the VCM current deviation that is used as a criterion for determining whether a seek operation may fail. The threshold value Th1 is determined when the magnetic disk device 1000 is manufactured and stored in a storage area (for example, the ROM 12).

[0081] If the absolute value of the VCM current deviation is greater than the threshold value Th1 (S201, Yes), the seek speed adjuster 102 sets the speed adjustment coefficient to the lower limit value (S202). The lower limit of the range in which the speed adjustment coefficient can be changed is predetermined. If the absolute value of the VCM current deviation is greater than the threshold value Th1, it can be assumed that the actual seek voltage margin is insufficient or there are signs that it will become insufficient. By changing the speed adjustment coefficient to the lower limit value, the seek speed adjuster 102 prevents consecutive seek errors or the occurrence of a seek error.

[0082] If the absolute value of the VCM current deviation amount is not greater than the threshold value Th1 (S201, No), the seek speed adjuster 102 determines whether or not the occurrence of a seek error has been detected (S203).

[0083] The operations from S203 onwards are executed each time one seek operation is completed. The occurrence of a seek error is determined by the seek error determiner 110. The seek speed adjuster 102 determines whether or not the seek error determiner 110 has determined that a seek error has occurred.

[0084] If the occurrence of a seek error is not detected (S203: No), the seek speed adjuster 102 determines whether the seek settling evaluation value is greater than a threshold value Th2 (S204).

[0085] When the seek operation is completed, the seek settling determinator 111 calculates a seek settling evaluation value. As described above, the seek settling evaluation value is the maximum absolute value of the position error during a set period immediately after the seek settling operation is completed. In S204, the seek speed adjuster 102 compares the sheet settling evaluation value obtained by the calculation of the seek settling determinator 111 with a threshold value Th2.

[0086] The threshold value Th2 is a value that is used as a criterion for determining whether the behavior of the position error in the seek settling operation is favorable for the subsequent positioning control. If the seek settling evaluation value exceeds the threshold value Th2, it indicates that the second target speed is too fast and the behavior of the position error in the seek settling operation has deteriorated.

[0087] The threshold value Th2 is determined when the magnetic disk device 1000 is manufactured and stored in a storage area (for example, the ROM 12).

[0088] If the occurrence of a seek error is detected (S203: Yes) or if the seek settling evaluation value is greater than threshold value Th2 (S204: Yes), the seek speed adjuster 102 sets the speed adjustment coefficient to the lower limit value (S202).

[0089] If the occurrence of a seek error is not detected (S203: No) and the seek settling evaluation value is not greater than the threshold value Th2 (S204: No), the seek speed adjuster 102 increments the first count value, which indicates the number of seek operations that have been executed, by 1 (S205). Then, the seek speed adjuster 102 determines whether the first count value is smaller than the upper limit value (S206).

[0090] The seek speed adjuster 102 uses the average value of the seek voltage margin over a set number of seek operations to control the amount of VCM current. In S206, the seek speed adjuster 102 checks whether the number of seek operations performed is less than the set number. That is, the set number is set as the upper limit.

[0091] If the first count value is smaller than the upper limit value (S206: Yes), the seek speed adjuster 102 accumulates the seek voltage margin (S207). If the number of seek operations performed since the start of counting using the first count value is M, the first count value is M. At the start of the process of S207, the seek speed adjuster 102 stores the total value of the seek voltage margins for the M-1 seek operations that have already been performed. In the process of S207, the seek speed adjuster 102 adds the latest seek voltage margin estimate obtained by the seek voltage margin estimator 108 to the total value of the seek voltage margins for the M-1 seek operations. As a result, the total value of the seek voltage margin for the M seek voltages is obtained after the process of S207.

[0092] When the first count value reaches the upper limit, the total value of the seek voltage margin is divided by the set number of times in the process of S210 described later, thereby calculating the average value of the seek voltage margin for the set number of seek operations.

[0093] After the process of S207, the seek speed adjuster 102 determines whether the absolute value of the VCM current deviation amount is greater than a threshold value Th3 (S208).

[0094] Threshold value Th3 is a threshold value for detecting signs of a seek operation failure. Threshold value Th3 is smaller than threshold value Th1. More specifically, even if the absolute value of the VCM current deviation amount does not satisfy threshold value Th1, if the number of times the absolute value of the VCM current deviation amount exceeds a certain level reaches a certain value (corresponding to threshold value Th5 described below), seek speed adjuster 102 determines that there is a sign of a seek operation failure. Therefore, that level is set as threshold value Th3. Threshold value Th3 is determined during the manufacture of magnetic disk device 1000 and stored in a storage area (for example, ROM 12).

[0095] If the absolute value of the VCM current deviation is greater than threshold value Th3 (S208, Yes), the seek speed adjuster 102 increments the second count value, which is the count value of the number of times the absolute value of the VCM current deviation exceeds threshold value Th3, by 1 (S209).

[0096] If the absolute value of the VCM current deviation amount is not greater than the threshold value Th3 (S208, No), or after the process of S209, the operation of updating the speed adjustment coefficient ends.

[0097] If the first count value is not smaller than the upper limit value (S206: No), that is, if the number of seek operations that have been performed reaches the set number, the seek speed adjuster 102 obtains the average value of the seek voltage margin by dividing the total value of the seek voltage margin for the set number of seek operations by the set number (S210).

[0098] With respect to the seek voltage margin, the seek speed adjuster 102 adjusts the speed adjustment coefficient so that the average value of the seek voltage margin is maintained at a predetermined low level. In the description of FIG. 4, the predetermined low level is defined as a range from threshold value Th4 to threshold value Th6, where threshold value Th4 is smaller than threshold value Th6. Threshold values ​​Th4 and Th6 are determined during the manufacture of the magnetic disk drive 1000 and stored in a storage area (for example, ROM 12).

[0099] The seek speed adjuster 102 determines whether the average value of the seek voltage margin is smaller than the threshold value Th4 (S211). If the average value of the seek voltage margin is smaller than the threshold value Th4 (S211: Yes), it can be assumed that the second target speed is too fast in terms of the seek voltage margin. Therefore, the seek speed adjuster 102 decreases the speed adjustment coefficient (S214).

[0100] If the average value of the seek voltage margin is not smaller than threshold value Th4 (S211: No), the seek speed adjuster 102 determines whether the second count value, i.e., the number of times the absolute value of the VCM current deviation amount exceeds threshold value Th3, is smaller than threshold value Th5 (S212).

[0101] If the second count value is not smaller than the threshold value Th5 (S212: No), that is, if the second count value reaches the threshold value Th5, it can be assumed that there is a sign that the seek operation will fail. Therefore, the seek speed adjuster 102 decreases the speed adjustment coefficient (S214).

[0102] If the second count value is smaller than threshold value Th5 (S212: Yes), the seek speed adjuster 102 determines whether the average value of the seek voltage margin is greater than threshold value Th6 (S213). If the average value of the seek voltage margin is greater than threshold value Th6 (S213: Yes), it can be assumed that there is room to increase the second target speed in terms of the seek voltage margin. Therefore, the seek speed adjuster 102 increases the speed adjustment coefficient (S215).

[0103] The method for decreasing the speed adjustment factor in the process of S214 and the method for increasing the speed adjustment factor in the process of S215 are not limited to a specific method. The seek speed adjuster 102 may increase or decrease the speed adjustment factor in preset increments.

[0104] If the average value of the seek voltage margin is not greater than the threshold value Th6 (S213: No), or after the process of S202, or after the process of S214, or after the process of S215, the seek speed adjuster 102 sets the first count value and the second count value to 0 (S216). Then, the operation of updating the speed adjustment coefficient ends.

[0105] 4, if the absolute value of the VCM current deviation amount is equal to threshold value Th1 in the process of S201, control transitions to S203. If the absolute value of the VCM current deviation amount is equal to threshold value Th1, control may transition to S202.

[0106] If the seek settling evaluation value is equal to the threshold value Th2 in the process of S204, the control proceeds to S205. If the seek settling evaluation value is equal to the threshold value Th2, the control may proceed to S202.

[0107] If the absolute value of the VCM current deviation amount is equal to threshold value Th3 in the process of S208, control skips the process of S209. If the absolute value of the VCM current deviation amount is equal to threshold value Th3 in the process of S208, control may transition to S209.

[0108] If the average value of the seek voltage margin is equal to the threshold value Th4 in the process of S211, the control proceeds to S212. If the average value of the seek voltage margin is equal to the threshold value Th4, the control may proceed to S214.

[0109] If the second count value is equal to the threshold value Th5 in the process of S212, the control proceeds to S214. If the second count value is equal to the threshold value Th5, the control may proceed to S213.

[0110] If the average value of the seek voltage margin is equal to the threshold value Th6 in the process of S213, the control proceeds to S216. If the average value of the seek voltage margin is equal to the threshold value Th6, the control may proceed to S215.

[0111] FIG. 5 is a graph showing an example of the distribution of instantaneous values ​​of the seek voltage margin estimated by the seek voltage margin estimator 108 according to an embodiment. The horizontal axis represents the seek distance as a percentage of the maximum value (full stroke distance). The vertical axis represents the seek voltage margin, i.e., the instantaneous value, obtained by a single estimation by the seek voltage margin estimator 108. From this graph, it can be seen that the instantaneous values ​​of the seek voltage margin obtained by estimation by the seek voltage margin estimator 108 vary greatly. To reduce the effects of variation, in this embodiment, the average value of the instantaneous values ​​of the seek voltage margin estimated over a set number of seek operations is calculated as shown in S210 of FIG. 4, and this average value is used to update the speed adjustment coefficient.

[0112] FIG. 6 is a graph showing an example of the distribution of VCM current deviations according to an embodiment. The horizontal axis represents the seek distance as a percentage of the maximum value (full stroke distance). From this graph, it can be seen that the variation in VCM current deviations is smaller than the variation in the estimated seek voltage margin. Because the VCM current deviations can be accurately determined and have small variations, using the VCM current deviations to control the speed adjustment coefficient allows for precise control of the VCM current to prevent signs of or actual shortage of the seek voltage margin. This allows the actual seek voltage margin to be maintained at a small enough level to avoid shortage, resulting in improved performance compared to using only the average seek voltage margin.

[0113] 7 is a diagram showing an example of the results of the operation of the magnetic disk device 1000 according to the embodiment. This diagram shows the temporal changes in the speed adjustment coefficient, performance, the number of seek errors, the average seek voltage margin, and the VCM current deviation. Note that the horizontal axis represents the number of times the speed adjustment coefficient has been updated, instead of time. IOPS (Input / Output Operations Per Second) is used here as an example of an index representing performance.

[0114] 7, the speed adjustment coefficient is finely adjusted, which keeps the average value of the seek voltage margin approximately constant, thereby reducing the number of seek errors and keeping performance approximately constant.

[0115] As described above, according to the embodiment, in a seek operation, the controller 13 obtains a VCM current command value based on the VCM current deviation amount.

[0116] More specifically, the controller 13 obtains a first target speed based on a position deviation, which is the difference between the position detection value and the target position. The controller 13 obtains a second target speed through a calculation using the first target speed and a speed adjustment coefficient, which is an example of a parameter value. The controller 13 calculates a VCM current command value so that the speed of the magnetic head 2 approaches the second target speed. The controller 13 obtains an actual VCM current value, which is the amount of VCM current generated according to the VCM current command value and supplied to the VCM drive circuit 14. The controller 13 then obtains a VCM current deviation by subtracting the actual VCM current value from the VCM current command value. The controller 13 then updates the speed adjustment coefficient, which is an example of a parameter value, based on the VCM current deviation.

[0117] This allows for precise control of the VCM current to avoid any signs of or actual seek voltage margin deficiency, thereby maintaining the actual seek voltage margin at a small enough level to avoid deficiency and improving performance compared to using only the average seek voltage margin.

[0118] Furthermore, according to the embodiment, the controller 13 obtains the second target speed by multiplying the first target speed by the speed adjustment coefficient.

[0119] Therefore, the time required for the seek operation can be reduced while maintaining the actual seek voltage margin at a small enough level that it is not insufficient.

[0120] Note that the method for obtaining the second target velocity from the first target velocity using the parameter value is not limited to multiplying the first target velocity by the speed adjustment coefficient. The controller 13 (specifically, the seek speed adjuster 102) may be configured to obtain the second target velocity by adding a speed adjustment value, which is another example of a parameter value, to the first target velocity (however, addition includes addition of a negative value, i.e., subtraction). In this case, the seek speed adjuster 102 updates the speed adjustment value based on at least the VCM current deviation. The seek speed adjuster 102 may also update the speed adjustment value based on an estimated seek voltage margin, a seek settling evaluation value, whether a seek error has occurred, and the VCM current deviation. The speed adjustment value may be updated in a manner similar to the method for updating the speed adjustment coefficient (e.g., the method shown in FIG. 4).

[0121] Furthermore, according to the embodiment, as shown in, for example, S201 and S202 of FIG. 4, the controller 13 changes the speed adjustment coefficient (or speed adjustment value), which is a parameter value, to a lower limit value when the absolute value of the VCM current deviation amount exceeds the threshold value Th1.

[0122] If the absolute value of the VCM current deviation is greater than the threshold value Th1, it can be inferred that the actual seek voltage margin is insufficient or there are signs that it may be insufficient. In such a case, by changing the speed adjustment coefficient (or speed adjustment value) to the lower limit, it becomes possible to prevent seek errors from occurring consecutively or at all.

[0123] 4, the controller 13 counts a second count value, which is the number of seek operations in which the absolute value of the VCM current deviation amount exceeds threshold value Th3. Then, the controller 13 decreases the speed adjustment coefficient (or speed adjustment value) as the second count value reaches threshold value Th5.

[0124] Since the second count value reaches the threshold value Th5, it can be estimated that there is a sign that the seek operation will fail, and therefore it is possible to prevent the seek operation from failing.

[0125] Furthermore, according to the embodiment, the controller 13 calculates the average value of the seek voltage margin for each set number of seek operations, as shown in, for example, S207, S210, S213, and S215 of FIG. 4. As shown in equation (1), the seek voltage margin is a voltage obtained by subtracting the amount of voltage drop in VCM4 from the power supply voltage. The controller 13 increases the speed adjustment coefficient (or speed adjustment value) when the average value of the seek voltage margin exceeds threshold value Th6.

[0126] Therefore, the time required for the seek operation can be reduced while maintaining the actual seek voltage margin at a small enough level that it is not insufficient.

[0127] Also, according to the embodiment, as shown in, for example, S207, S210, S211, and S214 of FIG. 4, the controller 13 reduces the speed adjustment coefficient (or speed adjustment value) when the average value of the seek voltage margin falls below the threshold value Th4.

[0128] Therefore, it is possible to maintain the actual seek voltage margin at a small enough level that it is not insufficient.

[0129] Furthermore, according to the embodiment, as shown in S204 and S202 in FIG. 4, the controller 13 changes the speed adjustment coefficient (or speed adjustment value) to the lower limit value when the seek settling evaluation value exceeds the threshold value Th2.

[0130] Therefore, it is possible to suppress the influence of factors such as the second target speed being too fast on the position error after the seek settling operation.

[0131] If the position error of the magnetic head 2 becomes large during a write operation, the data to be written to the target track 5 may be written at a position that extends beyond the adjacent track 5 of the target track 5, potentially destroying the data on the adjacent track 5. In other words, the position error of the magnetic head 2 is controlled more strictly during a write operation than during a read operation. Therefore, the calculation of the second target speed using the first target speed and parameter values, and the operation of updating the parameter values ​​may be performed during a seek operation for a read operation, but may not be performed during a seek operation for a write operation. In such a case, it is possible to prevent the position error during a write operation from exceeding the allowable range due to factors such as an excessively high target speed.

[0132] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0133] 1 magnetic disk, 2 magnetic head, 3 arm, 4 VCM, 5 track, 6 servo sector, 7 servo area, 8 data area, 9 signal processing circuit, 10 position detection circuit, 11 CPU, 12 ROM, 13 controller, 14 VCM drive circuit, 15 VCM current detection circuit, 16, 18 A / D conversion circuit, 17 power supply voltage detection circuit, 101 target speed table, 102 seek speed regulator, 103 VCM controller, 104 VCM driver, 105 VCM actual current detector, 106 VCM resistance estimator, 107 power supply voltage detector, 108 seek voltage margin estimator, 109 head speed estimator, 110 seek error determiner, 111 seek settling determiner, 112, 113, 114 subtractor, 1000 magnetic disk device.

Claims

1. A magnetic disk, an arm provided with a magnetic head for accessing the magnetic disk; a motor that moves the arm to move the magnetic head in the radial direction of the magnetic disk; a drive circuit that generates a first current for driving the motor in an amount corresponding to an instruction value and supplies the generated first current to the motor; a current detection circuit that detects the amount of the first current generated by the drive circuit; a controller that, during a seek operation, acquires an instruction value for moving the radial position of the magnetic head closer to a target position based on a deviation amount of the first current detected by the current detection circuit from the instruction value, and inputs the acquired instruction value to the drive circuit; A magnetic disk device comprising:

2. a position detection circuit for detecting the radial position of the magnetic head; Furthermore, The controller obtaining a first target velocity of the magnetic head in the radial direction based on a difference between the position detected by the position detection circuit and a target position of the magnetic head in the radial direction; obtaining a second target velocity of the magnetic head in the radial direction by calculation using the first target velocity and a parameter value; calculating a first value that is the amount of the first current so that the radial velocity of the magnetic head approaches the second target velocity; inputting the first value as the instruction value to the drive circuit; calculating the deviation amount by subtracting, from the first value, a second value that is the amount of the first current generated by the drive circuit in accordance with the indication value of the first value and detected by the current detection circuit; updating the parameter value based on the deviation amount; 2. The magnetic disk drive according to claim 1.

3. the controller obtains the second target speed by multiplying or adding the first target speed by the parameter value; 3. The magnetic disk drive according to claim 2.

4. the controller changes the parameter value to a lower limit value of the parameter value when the absolute value of the deviation amount exceeds a first threshold value; 4. The magnetic disk drive according to claim 3.

5. the controller counts a first number, which is the number of times the seek operation has occurred in which the absolute value of the deviation has exceeded a second threshold, and decreases the parameter value when the first number reaches a third threshold.

4. The magnetic disk drive according to claim 3.

6. the drive circuit generates the first current using power supplied from a power supply; the controller calculates an average value of a voltage margin for the set number of seek operations each time the seek operations are performed a set number of times, the voltage margin being a value obtained by subtracting an amount of voltage drop in the drive circuit from the voltage of the power, and increases the parameter value when the average value exceeds a fourth threshold value; 4. The magnetic disk drive according to claim 3.

7. the drive circuit generates the first current using power supplied from a power supply; the controller calculates an average value of a voltage margin for the set number of seek operations each time the seek operations are performed a set number of times, the voltage margin being a value obtained by subtracting an amount of voltage drop in the drive circuit from the voltage of the power, and decreases the parameter value when the average value falls below a fifth threshold value; 4. The magnetic disk drive according to claim 3.

8. the controller changes the parameter value to a lower limit value when an absolute value of the difference between the position detected by the position detection circuit and the target position in the radial direction of the magnetic head exceeds a sixth threshold value during a set period immediately after the completion of the seek operation; 4. The magnetic disk drive according to claim 3.

9. the seek operation is a seek operation for a read operation, 9. The magnetic disk drive according to claim 1.

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