JP2004342316A - Magnetic disk unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the vibrations of a magnetic head while compensating eccentricity of a magnetic disk in a magnetic disk unit in which the magnetic head is positioned along a rotation circle around the rotation center of the magnetic disk. <P>SOLUTION: This magnetic disk unit includes a magnetic disk 14 having servo information and rotated around the rotation center, a magnetic head 13 reading out information of the magnetic disk 14, a positioning means 10 positioning the magnetic head 13 radially of the magnetic disk 14, a control means 7 controlling the positioning means 10 conforming to the position error by servo information of the magnetic head, and a compensation table storing the measured rotational frequency component R0 of the magnetic disk 14 and a high order frequency component R1 of higher frequency than the rotational frequency. The control means follows up the rotational frequency component R0 of the compensation table and feedforward-controls the positioning means 10 so as to eliminate the high order frequency component R1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic disk drive for positioning a magnetic head on a track of a magnetic disk, and more particularly, to a magnetic disk drive for positioning a magnetic head along a rotation circle around the rotation center of the magnetic disk.

  An increase in storage capacity is required for magnetic disk devices. In order to increase the storage capacity, it is necessary to reduce the track pitch of the magnetic disk. In order to reduce the track pitch, it is necessary to write a track having servo information (servo track) at an accurate position. There is a need to provide a magnetic disk drive having such accurate servo tracks at low cost.

  FIG. 13 is an explanatory diagram of the eccentric operation of the magnetic disk, FIG. 14 is an explanatory diagram of the conventional technology, and FIG. 15 is a configuration diagram of the conventional technology. In order to write a servo track at an accurate position, conventionally, it has been necessary to provide each magnetic disk device with a function of writing a servo track at an accurate position. However, when such a function is given to each magnetic disk device, the price of each magnetic disk device increases.

  For this reason, after writing servo tracks on a magnetic disk by using a servo track writer, it has been studied to mount a magnetic disk on which the servo tracks are written in individual devices.

  That is, a servo track is written on a magnetic disk by a servo track writer having high positioning accuracy. Then, a magnetic disk on which servo tracks are written is attached to each magnetic disk device. With this configuration, it is not necessary to provide each magnetic disk device with a function of writing servo tracks with high positioning accuracy, so that a magnetic disk device having servo tracks with a narrow track pitch can be provided at low cost.

  In the case where the magnetic disk on which the servo tracks are written is mounted on an individual device, as shown in FIG. In some cases, -1 does not coincide with the rotation circle locus 14-2 about the rotation center of the magnetic disk 14. That is, since the magnetic disk 14 on which the servo tracks are written is mounted on the apparatus, the servo circular locus 14-1 does not match the rotational circular locus 14-2 of the magnetic disk 14 even if there is a slight mounting error.

  Due to the mounting position error of the magnetic disk 14, eccentricity of the magnetic disk occurs. As shown in FIG. 13, the magnetic head 13 attached to the arm 17 moves in the radial direction of the magnetic disk. The magnetic head 13 located along the rotating circular locus 14-2 of the magnetic disk 14 is controlled by the servo information of the servo track 14-1, and is positioned along the servo track 14-1.

  Therefore, as shown in FIG. 14, a track deviation including a track eccentricity occurs. Since the track deviation includes a track eccentric component, the position error of the magnetic head 13 increases. For this reason, the magnetic head 13 easily vibrates.

  In order to prevent this, there is an attempt to apply an eccentricity control method. As shown in FIG. 15, the magnetic disk device 12 includes a magnetic disk 14 and a spindle motor 15 that rotates the magnetic disk 14. The magnetic head 13 is provided at the tip of the arm 17. The arm 17 is moved by a rotary actuator (VCM) 10, and the magnetic head 13 is positioned at a position on the magnetic disk 14 in the radial direction.

  The head position detector 20 detects a head position from a read signal of the magnetic head 13. The control calculation unit 25 performs a control calculation (PID calculation or the like) on the position error to calculate a control current. The control current is amplified by the amplifier 23 and drives the VCM 10.

  In this control system, with the arm 17 fixed, servo information is read by the magnetic head 13 and a position error is measured. The position error (track deviation) for one round of the magnetic disk 14 is read and stored in the memory 22. This track deviation is shown in FIG. During normal control, the VCM 10 is controlled by adding the track deviation of the memory 22 to the position error from the magnetic head 13.

  In this way, the eccentric component (track deviation) is measured, and the feedforward control is performed. For this reason, the magnetic head 13 is positioned along the locus of rotation. Therefore, the position error can be reduced. As described above, in the related art, the track deviation is measured, and the measured track deviation is subjected to feedforward control to perform positioning along a rotating circle locus (for example, see Patent Document 1).

  FIG. 16 is an explanatory view of a problem of the conventional technique (part 1), and FIG. 17 is a problem of the conventional technique (part 2). When the track pitch is reduced, the size of the core width of the magnetic head affects the demodulated output. There is a limit to reducing the core width of the magnetic head. For this reason, the sensitivity of the detection portion of the magnetic head varies.

  Accordingly, as shown in FIG. 16, the demodulation displacement does not show a linear characteristic with respect to the displacement of the magnetic head. That is, when the magnetic head is located at the track boundary, the servo demodulation displacement becomes discontinuous. This is because when the track pitch is reduced, the sensitivity of the detection portion of the magnetic head varies.

In particular, there is a case where a read / write head such as an MR head is used to correct a core position shift between the write head and the read head so as to correct the core position shift. In this case, the magnetic head is easily located at the track boundary. The discontinuous portion of the servo demodulation displacement indicates a position error of a high frequency component. Further, when the feedforward control is performed by the track eccentricity, as shown in FIG. 17, the eccentric component is compensated, but the high frequency component is emphasized. Therefore, as shown in FIG. 17, the magnetic head vibrates with respect to the track center. As a result, the magnetic head is over-vibrated, causing a reduction in positioning accuracy.
International Publication WO93 / 06595

  An object of the present invention is to provide a magnetic disk device for improving the positioning accuracy while correcting eccentricity of a magnetic disk.

  Another object of the present invention is to provide a magnetic disk device for preventing the magnetic head from vibrating while correcting the eccentricity of the magnetic disk.

  Still another object of the present invention is to provide a magnetic disk drive for removing a high-order frequency component of a position error while correcting eccentricity of a magnetic disk.

  In order to achieve this object, the present invention provides a magnetic disk having servo information and rotating about a rotation center, a magnetic head for reading information on the magnetic disk, and positioning the magnetic head in a radial direction of the magnetic disk. Positioning means, a position error is calculated according to the servo information read by the magnetic head, a control current is created from the position error, and a control means for feedback-controlling the positioning means is provided. A correction table for storing a rotational frequency component of the disk and a higher-order frequency component higher than the rotational frequency; Then, the control means adds the rotation frequency component of the correction table to the position error or the control current, and subtracts the higher-order frequency component of the correction table from the position error or the control current, and The positioning means is feed-forward controlled so as to follow the frequency component and eliminate the higher-order frequency component.

  According to the present invention, since the control is performed in accordance with the rotational frequency component, the eccentricity of the magnetic disk can be accurately corrected. Further, since control is performed by eliminating higher-order frequency components generated at discontinuous portions of the servo demodulation displacement, vibration of the magnetic head at track boundaries can be prevented.

  In addition, since the correction table stores the rotational frequency component and the higher-order frequency component measured separately, the correction table can accurately follow the rotational frequency component and accurately eliminate the higher-order frequency component. Therefore, eccentricity control with improved positioning accuracy can be performed.

  FIG. 1 is a configuration diagram of a magnetic disk drive according to an embodiment of the present invention, FIG. 2 is a control block diagram of a servo circuit of FIG. 1, and FIG. 3 is an operation flow diagram of an embodiment of the present invention. 4 is an explanatory diagram of a control operation of the configuration of FIG. 2, and FIG. 5 is an explanatory diagram of a higher-order eccentricity compensation operation of the configuration of FIG.

  As shown in FIG. 1, the magnetic disk device 12 includes a magnetic disk 14 and a spindle motor 15 that rotates the magnetic disk 14. A plurality of magnetic disks 14 are mounted on a spindle motor 15. As shown in FIG. 4, a servo track Y is written on the magnetic disk 14 in advance.

  The track Y is divided into a plurality of (for example, 128) sectors. Each sector has a servo area on which servo information is written and a data area for writing data. The magnetic disk 14 is attached to the spindle motor 15 after the servo information has been written. Due to the eccentricity of the magnetic disk 14, the circular locus of the servo track Y differs from the rotational circular locus Z about the rotation center B of the magnetic disk 14, as shown in FIG.

  Returning to FIG. 1, the magnetic head 13 is provided at the tip of the arm 17. The arm 17 is moved by a rotary actuator (VCM) 10, and the magnetic head 13 is positioned at a position on the magnetic disk 14 in the radial direction.

  The read / write channel 3 converts a detection signal of the magnetic head 13 into a read signal and converts write data into a write signal of the magnetic head 13. The hard disk controller 4 controls data transfer with the host. The RAM 5 is a memory used by the hard disk controller 4.

  The microprocessor (MPU) 6 controls the entire magnetic disk device. The servo circuit 7 has a digital signal processor (DSP) and peripheral circuits. The servo circuit 7 servo-controls the VCM 10 according to a position signal from the magnetic head 13. The servo circuit 7 controls the rotation of the spindle motor 15.

  The memory 8 stores eccentricity data at each time in one round of the magnetic disk 14. The eccentricity data in the memory 8 is given to the servo circuit 7.

  As shown in FIG. 2, the position signal detection unit 20 detects a head position from a read signal of the magnetic head 13. The amplifier 23 drives the VCM 10 by amplifying the control current from the DSP 7.

  The memory 8 stores an eccentric component R0 and a high-frequency deviation component R1. The eccentric component is a rotational frequency component of the magnetic disk in the radial direction, and is stored in the first area 81 of the memory 8. The high-frequency deviation component is a higher-order frequency component having a frequency higher than the rotation frequency of the magnetic disk, and is stored in the second area 82 of the memory 8.

  In the DSP 7, the first calculation unit 70 subtracts the detected position from the target position and calculates a position error. The second calculation unit 71 subtracts the high-frequency deviation component R1 of the memory 8 from the position error. Thereby, the high frequency deviation component is excluded from the control system. The control calculation unit 72 performs a control calculation (PID calculation) on the position error from which the high-frequency deviation component has been removed, and calculates a control current.

  The third arithmetic unit 73 adds the eccentric component R0 of the memory 8 to the control current. Thus, the eccentricity is controlled so as to follow the eccentricity component R0.

  The measuring unit 74 measures the eccentric component R0 from the control current and stores it in the first area 81 of the memory 8, as described later. The measuring unit 74 measures the high-frequency deviation component R1 from the position error and the control current, and stores the high-frequency deviation component R1 in the second area 82 of the memory 8.

  Each of the arithmetic units 70, 71, 73, the control arithmetic unit 72, and the measuring unit 74 is a block diagram illustrating the processing performed by the DSP 7.

  The operation will be described with reference to FIG.

  (S1) The measuring unit 74 measures the eccentric component R0 from the control current and stores the eccentric component R0 in the first area 81 of the memory 8.

  (S2) The measurement unit 74 measures the high-frequency deviation component R1 from the position error and the control current, and stores it in the second area 82 of the memory 8.

  (S3) The DSP 7 performs servo control by following the eccentric component and excluding the high-frequency deviation component. That is, the first calculation unit 70 calculates the position error by subtracting the detected position from the target position.

  The second calculation unit 71 subtracts the high-frequency deviation component R1 of the memory 8 from the position error. Thereby, the high frequency deviation component is excluded from the control system. The control calculation unit 72 performs a control calculation (PID calculation) on the position error from which the high-frequency deviation component has been removed, and calculates a control current. The third arithmetic unit 73 adds the eccentric component R0 of the memory 8 to the control current. The control current to which the eccentric component R0 is added is given to the amplifier 23 and drives the VCM 10.

  As described above, in order to control to follow the eccentric component R0, the position of the magnetic head 13 is controlled along the rotation circle locus Z as shown in FIG. Therefore, even if the magnetic disk is eccentric, the position error can be reduced. Thereby, the position control of the magnetic head can be kept stable.

  Further, the demodulation displacement at the track boundary is discontinuous, and a higher-order frequency component is generated. Since high-frequency deviation components, which are higher-order frequency components, are eliminated, transient response due to higher-order frequencies can be prevented. In addition, since the high-frequency deviation component is eliminated, high-frequency emphasis of the control system can be prevented. Therefore, as shown in FIG. 5, vibration of the locus of the magnetic head 13 can be prevented.

  In this example, an eccentric component is added to the control current. There is also a method of adding an eccentric component to the position error. However, the position error is compressed by the control calculation of the control calculation unit 72. Therefore, the eccentric component cannot be accurately followed. In this example, since the eccentric component is added to the control current after compression, it is possible to directly follow the eccentric component. Further, even if the eccentric component is large, it is possible to control to follow the eccentric component.

  Further, the high-frequency deviation component is measured while following the measured eccentric component. Therefore, since the high-frequency deviation component is measured from the position error from which the eccentric component has been removed, the high-frequency deviation component can be accurately measured.

  Further, a high-frequency deviation component is removed from the position error. Since unnecessary high frequency deviation components are eliminated at the input stage of the control system, it is possible to prevent adverse effects on the control system due to high frequency deviation components.

  6 is a block diagram at the time of eccentricity measurement, FIG. 7 is a characteristic diagram of the inverse notch filter of FIG. 6, and FIG. 8 is a control block diagram at the time of high-frequency deviation measurement.

  The measurement process of the eccentric component will be described with reference to FIGS.

  As shown in FIG. 6, an inverse notch filter 74-1 is provided in series with the control operation unit 72. As shown in FIG. 7, the open-loop characteristic of the inverse notch filter 74-1 has a high gain g at the rotational frequency (fundamental frequency) f1 of the magnetic disk. Since the gain of only the fundamental frequency component of the position error is high, the control system follows the eccentricity.

  The averaging unit 74-2 of the DSP 7 averages the driving current output from the control calculation unit 72.

  Thereby, the eccentric component of the drive current is detected. Next, the Fourier transform unit 74-3 of the DSP 7 performs Fourier transform of the drive current. Assuming that the discrete Fourier transform value of the discrete time function X (x) is Y (x), the discrete Fourier transform value is represented by the following equation (1).

  Note that Re (Yk) is the real part of the discrete Fourier transform, and Im (Yk) is the imaginary part of the discrete Fourier transform.

  The fundamental wave extracting unit 74-5 extracts a fundamental wave component from the discrete Fourier transform. At this time, if the sampling frequency of the control system is Fs, the frequency of the fundamental wave is F1, and N is the number of sectors, the frequency Fk of the discrete Fourier transform Yk is expressed by the following equation (2).

Fk = Fs · k / N = k · F1 (2)
According to equation (2), Fk indicates a fundamental wave or a harmonic. That is, when the measurement cycle is set to one rotation of the magnetic disk and the number of samples is set to the number of sectors and Fourier transform is performed, the frequency of each Fourier coefficient becomes a fundamental wave or a harmonic. Therefore, the fundamental wave component can be extracted by using the Fourier coefficient Y1 (Y (1)) of the fundamental wave frequency F1.

  Next, the inverse Fourier transform unit 74-6 performs inverse Fourier transform using the fundamental wave component to reproduce an eccentric component (drive current). The inverse Fourier transform is represented by the following equation (3).

  Re (Xk) is the real part, and Im (Xk) is the imaginary part.

  The inverse Fourier transform value for each sample is stored in the first area 81 of the memory 8. Here, the inverse notch filter 74-1, the averaging unit 74-2, the Fourier transform unit 74-3, the fundamental wave extractor 74-5, and the inverse Fourier transform unit 74-6 block processing performed by the DSP 7. It is.

  In this way, an eccentric component is extracted from the drive current by Fourier transform. Since the fundamental wave is extracted by the Fourier transform, a sharp characteristic is not required for the inverse notch filter.

  Next, the measurement processing of the high-frequency deviation component will be described with reference to FIG.

  Assuming that the transfer function of the control operation unit 72 is “C” and the transfer function of the VCM 10 is “P”, the inverse characteristic of the disturbance compression characteristic of the control system is (1 + CP). Therefore, the eccentric component A is represented by the following equation (4).

A = (1 + CP) × position error (4)
In the equation (4), since (C × position error) is a drive current, the equation (4) is modified to obtain the equation (5).

A = Position error + P × Drive current (5)
When the calculation is performed by the equation (5), the calculation amount is reduced and the calculation error due to the cancellation of the digit is small as compared with the equation (4).

  As shown in FIG. 8, the control system includes a first calculation unit 70, a control calculation unit 72, and a third calculation unit 73. That is, the first calculation unit 70 calculates the position error. The control calculation section 72 calculates the drive current from the position error. The third calculation unit 73 adds the eccentric component R0 to the drive current. Therefore, the VCM 10 follows the eccentric component.

  In this state, the averaging unit 75-1 of the DSP 7 averages the driving current output from the control calculation unit 72. The averaging unit 75-2 of the DSP 7 averages the position error output from the first arithmetic unit 70. Next, the Fourier transform unit 75-3 of the DSP 7 performs Fourier transform of the drive current. The Fourier transform unit 75-4 of the DSP 7 performs Fourier transform of the position error.

  The Fourier transform unit 75-6 of the DSP 7 performs a Fourier transform on the transfer function (filter function) P of the VCM 10. The multiplier 75-7 of the DSP 7 multiplies the Fourier transform value of the drive current by the Fourier transform value of the transfer function. The adder 75-8 of the DSP 7 adds the Fourier transform value of the position error and the multiplication result. Next, an inverse Fourier transform unit 75-9 performs an inverse Fourier transform on the addition result to reproduce a high-frequency deviation component (position error) R1.

  The inverse Fourier transform value for each sample is stored in the second area 82 of the memory 8. Here, the averaging units 75-1, 75-2, the Fourier transform units 75-3, 75-4, 75-6, the multiplying unit 75-7, the adding unit 75-8, and the inverse Fourier transform unit 75-9 are: The processing performed by the DSP 7 is a block.

  In this way, a high-frequency deviation component is extracted from the driving current and the position error by the Fourier transform. Since the higher-order deviation component is measured while controlling to follow the eccentricity, the higher-order deviation component can be measured without being affected by the eccentricity. Since the higher-order deviation component is measured using the inverse model of the control system, the higher-order deviation component can be extracted by calculation.

  Further, since the Fourier transform is performed, an initial value is not required. Because of Fourier transform, the influence of transient response is small. Therefore, the higher-order deviation component can be accurately measured.

  In this example, the higher-order deviation component is measured from the above equation (5), but the above equation (4) may be used.

  FIGS. 9A and 9B are control block diagrams of another embodiment of the present invention.

  As shown in FIG. 9A, the memory 8 stores a position feedforward value obtained by subtracting the higher-order deviation component R1 from the eccentricity component R0. Then, the second calculation unit 71 adds the position feedforward value of the memory 8 to the position error of the first calculation unit 70. The control calculation unit 72 converts the corrected position error into a drive current.

  Also, as shown in FIG. 9B, the memory 8 stores a current feedforward value obtained by subtracting the high-order deviation component R1 from the eccentric component R0. Then, the third calculation unit 73 adds the current feedforward value of the memory 8 to the drive current of the control calculation unit 72.

  Even if the control system is configured in this manner, position control that follows the eccentric component and eliminates the higher-order deviation component can be performed.

  Next, this DSP can measure the frequency characteristics of the control system. 10 (A) and 10 (B) are control block diagrams of frequency measurement, FIG. 11 is a processing flowchart for frequency measurement, and FIG. 12 is an explanatory diagram of the frequency measurement operation.

  In FIGS. 10A and 10B, the transfer function of the control operation unit 72 is “C”, and the transfer function (mechanical characteristics) of the VCM 10 is “P”. The control operation unit 72 and the VCM (control target) 10 constitute a control system. The control calculation unit 72 converts the position error Pes into a drive current Cur. The position error Pes of the VCM 10 is input to the control calculation unit 72.

  The measurement noise R is added to the control system. In FIG. 10A, measurement noise R is added to the position. In FIG. 10B, the measurement noise R is added to the current.

  The measurement method adds measurement noise to the control system. Capture the waveform at that time. The measured waveform is Fourier-transformed, a complex Fourier coefficient is calculated, and a frequency characteristic is obtained.

  The mechanical characteristics P, the open-loop characteristics Z1, the closed-loop characteristics Z2, and the disturbance compression characteristics Z3 are obtained from the waveforms R, X, Y, Pes, and Cur by the following equations.

  P = Pes / CurZ1 = Y / XZ2 = Y / RZ3 = X / R At this time, if there is a primary eccentricity and a higher-order deviation, the eccentricity and the deviation component are also included in the measurement result, and the measurement accuracy is reduced. In order to increase measurement accuracy, it is necessary to remove eccentricity and deviation components from measurement results. FIG. 11 is a process flowchart for easily removing the eccentric component.

  (S10) The measurement frequency is initialized. That is, the parameter N is set to the number of sectors, and the frequency parameter k is set to “1”.

  (S11) The n-th measurement noise waveform Sn is calculated by the following equation. The noise waveform is a sine wave as shown in FIG.

  Sn = 1 / N · G · sin (−2πn / N) where G is the amplitude added to the control system.

  Next, the averaging integrated variables PeSUMn and CurSUMn are initialized to “0”. Further, the phase shift amount P1 of the measurement noise is initialized to “0”.

  (S12) The phase of the measurement noise is shifted and added to the control system. That is, the n-th noise waveform Nn to be added is the m-th noise waveform Sm. Note that m = n-P1.

  (S13) A measurement waveform for one cycle is fetched. That is, the position PESn and the drive current CURn are taken.

  (S14) The phase of the measured waveform is returned and integrated. That is, the n-th position integrated variable PesSUMn is updated by adding the m-th measured position PESn to the n-th position integrated variable PesSUMn. Further, the m-th measured current CURn is added to the n-th current integrated variable CurSUMn to update the n-th current integrated variable CurSUMn.

  (S15) The phase shift amount P1 of the measurement noise is shifted by one sector. That is, the phase shift amount P1 is updated to (P1 + 1).

  (S16) It is determined whether the phase shift amount P1 is smaller than the number N of sectors. If the phase shift amount P1 is smaller than the number N of sectors, the process returns to step S12.

  (S17) When the phase shift amount P1 is equal to or more than the number N of sectors, it means that the measurement at all the phase shift amounts has been completed at that frequency. Therefore, the measured waveform is averaged. That is, the average measurement position PesRROn is obtained by PesSUMn / N. The average measurement current CurRROn is obtained from CurSUMn / N.

  (S18) Fourier transform the measured waveform. That is, the real part Re (PesDFTk) and the imaginary part Im (PesDFTk) of the Fourier coefficient at the measurement position are obtained from the average measurement position PesRROn. Similarly, the real part Re (CurDFTk) and the imaginary part Im (CurDFTk) of the Fourier coefficient of the measured current are obtained from the average measured current CurRROn. Here, the Fourier transform to be obtained is only the measurement frequency.

  (S19) The frequency characteristic is obtained in a complex format. That is, the mechanical characteristic P is obtained by a value obtained by dividing the Fourier coefficient PeDFTk of the position by the Fourier coefficient CurDFTk of the current. The measurement frequency Fk at that time is obtained by K / N · Fs. Note that Fs is a sample frequency.

  (S20) The measurement frequency variable k is changed. That is, the measurement frequency variable k is updated to (k + 1).

  (S21) The measured frequency variable k is compared with the number of sectors N. If the measured frequency variable k is smaller than the number of sectors N, the process returns to step S11. When the measurement frequency variable k is equal to or larger than the number of sectors, the measurement of all frequencies has been completed. Therefore, the measurement ends.

  Thus, as shown in FIG. 12A, a sine wave is used as a measurement noise wave. A sine wave whose phase is sequentially shifted is applied as noise. The measurement waveform when these sine waves are applied is as shown in FIG. When these are superimposed, the sine wave component, that is, the eccentricity (and deviation) component of the disk is removed. That is, the measurement noise wave is sequentially shifted and given, and then added to the measurement waveform of the original phase before the measurement waveform is shifted. Thereby, it becomes possible to measure the frequency characteristic from which the eccentric (and deviation) component of the disk has been removed.

  In addition to the above-described embodiment, the present invention can be modified as follows.

  (1) The method of separating and measuring the eccentric component and the higher-order deviation component has been described in the embodiment, but other methods can be used.

  (2) The method of measuring the eccentric component has been described with the configuration of FIG. 6, but the configuration of FIG. 8 is also applicable.

  Although the embodiments of the present invention have been described above, various modifications are possible within the scope of the gist of the present invention, and these are not excluded from the scope of the present invention.

  In the present invention, the control is performed following the rotational frequency component, so that the eccentricity of the magnetic disk can be accurately corrected. The vibration of the magnetic head can be prevented, the rotational frequency component can be accurately followed, and the high-order frequency component can be accurately eliminated. For this reason, eccentricity control with improved positioning accuracy becomes possible, which contributes to the performance improvement of the magnetic disk drive.

1 is a configuration diagram of a magnetic disk device according to an embodiment of the present invention. FIG. 2 is a control block diagram of the configuration of FIG. 1. FIG. 3 is an operation flowchart of the configuration of FIG. 2. FIG. 3 is an explanatory diagram of a control operation of the configuration of FIG. 2. FIG. 3 is an explanatory diagram of a higher-order deviation compensation operation of the configuration in FIG. 2. It is a block diagram at the time of the eccentricity measurement of one Embodiment of this invention. FIG. 7 is a characteristic diagram of the inverse notch filter of FIG. 6. It is a control block diagram at the time of the high order deviation measurement of one embodiment of the present invention. FIG. 13 is a control block diagram of another embodiment of the present invention. FIG. 4 is a control block diagram of frequency measurement according to the present invention. FIG. 5 is a processing flowchart of frequency measurement according to the present invention. FIG. 12 is a diagram illustrating the operation of the process in FIG. 11. It is explanatory drawing of an eccentric operation. It is explanatory drawing of a prior art. FIG. 2 is a configuration diagram of a conventional technique. FIG. 7 is a diagram (part 1) for explaining a problem of the conventional technique. FIG. 11 is a diagram (part 2) for explaining a problem of the conventional technique.

Explanation of reference numerals

3 read / write channel 4 hard disk controller 7 servo circuit 8 memory 10 voice coil motor 13 magnetic head 14 magnetic disk 15 spindle motor

Claims (2)

A magnetic disk having servo information and rotating about a rotation center,
A magnetic head for reading information on the magnetic disk;
Positioning means for positioning the magnetic head in a radial direction of the magnetic disk;
Control means for calculating a position error according to the servo information read by the magnetic head, creating a control current from the position error, and performing feedback control on the positioning means,
A rotational frequency component of the magnetic disk obtained by measurement, and a correction table that stores a higher-order frequency component of a frequency higher than the rotational frequency,
The control means adds the rotational frequency component of the correction table to the position error or the control current, and subtracts the higher-order frequency component of the correction table from the position error or the control current, A magnetic disk drive, wherein the positioning means is feedforward controlled so as to follow a component and eliminate the higher-order frequency component. The correction table controls the positioning means so as to follow the measured rotational frequency component of the magnetic disk and the measured rotational frequency component based on the position error according to the servo information of the magnetic head. 2. The magnetic disk drive according to claim 1, wherein a high-order frequency component having a frequency higher than the measured rotation frequency is stored based on the position error of the servo information of the magnetic head.

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