JP2008052794A - Magnetic disk unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic disk unit in which an increase of convergence time is suppressed and desired performance can be exhibited regardless of setting of an initial value. <P>SOLUTION: A circuit to control the position of a magnetic head 5 is a frequency estimator which estimates the frequency of an error signal. The magnetic disk unit includes the frequency estimator which sets an initial value for the beginning, and controls the update value of the frequency to be estimated in such a manner that the convergence rate of the frequency to be estimated with respect to the signal frequency to be removed is constant regardless of the difference between the initial value and the frequency of the signal to be removed included in the error signal, and a disturbance remover which generates and outputs a signal in reverse phase to the signal of the frequency component included in the error signal and estimated by the frequency estimator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic disk device such as a hard disk.

  In a magnetic disk device such as a hard disk, data is recorded on a circular orbit (track) formed on a disk (disk) that is a magnetic recording medium. Therefore, in order to write or read this data, positioning control for moving the magnetic head to the track position is required. In such a head positioning mechanism, various countermeasures against periodic disturbance caused by various factors are taken.

  However, these disturbances include those in which the frequency or the like is difficult to specify in advance, such as vibration received by the magnetic disk device from the outside, and disturbances in which the frequency varies with time. On the other hand, the follow-up control for maintaining the position of the magnetic head with respect to the target track is designed for the purpose of suppressing disturbance over a wide band. For this reason, there is a case where the suppression capability is not sufficient for the disturbance of a specific frequency component.

  In recent years, magnetic disk devices have come to be used in a wide range of fields such as portable computers, mobile phone devices, and car navigation systems, and there is a need for a technique that sufficiently suppresses external vibrations.

Therefore, Patent Document 1 discloses a method of removing a disturbance by using a resonance filter that removes a signal of a specific frequency component, repetitively updating the resonance frequency of the resonance filter, and gradually approaching the disturbance frequency. Yes. Non-Patent Document 1 discloses a technique of changing the update width so as to minimize the square of the position error when performing this repetitive update.
JP 2003-109335 A M. Kisaka, "FrequencyChasing Peak Filter", IEE of Japan Technical Meeting Record, No.IIC-04-70, pp.19-23 (2004)

  According to the method disclosed in Non-Patent Document 1, the resonance frequency of the resonance filter can be made closer to the target frequency as compared with the case where the update width is made constant while increasing the speed of convergence. Performance can be improved. However, even with the method disclosed in Non-Patent Document 1, since the convergence time increases as the initial value of the estimated frequency increases from the target frequency, the convergence time increases depending on the relationship between the initial value and the disturbance, and the desired performance is obtained. May not be possible.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic disk device capable of suppressing an increase in convergence time and exhibiting desired performance regardless of the setting of an initial value. To do.

  The present invention for solving the problems of the above conventional example is a magnetic disk device, wherein a magnetic disk medium in which data is recorded along a predetermined trajectory, and a relative movement with respect to the magnetic disk medium, The magnetic head for writing and reading the data and the input of an error signal indicating the positional error of the magnetic head with respect to the predetermined trajectory are received, and the position of the magnetic head is adjusted so that the magnetic head is positioned on the predetermined trajectory. A position control circuit for controlling, and the position control circuit estimates a frequency of the error signal, and initially sets an initial value and includes the initial value and the error signal. The estimation is performed so that the convergence rate of the estimated frequency with respect to the signal frequency of the removal target is constant regardless of the difference from the frequency of the signal to be removed. A frequency estimator that controls the update width of the wave number, and a disturbance eliminator that generates and outputs a signal having a phase opposite to that of the frequency component estimated by the frequency estimator, included in the error signal. .

  Embodiments of the present invention will be described with reference to the drawings. The magnetic disk device according to the embodiment of the present invention is a hard disk device as shown in FIG. 1, for example, and includes a magnetic disk medium 1, a spindle motor (SPM) 2, a magnetic head 5, a carriage 6, and a suspension 7. A flexible circuit 8, a head signal amplifier 9, a modem 10, a voice coil motor (VCM) 11, a microprocessor (MPU) 14, a storage unit 16, and a digital / analog conversion circuit (D / A conversion). Circuit) 18, drive amplifier 19, interface controller 20, and host-side controller 21. Note that the D / A conversion circuit 18, the modem 10, the MPU 14, the storage unit 16, and the interface controller 20 are connected to each other via the bus line 15.

  The magnetic disk medium 1 is rotationally driven by the SPM 2. On the magnetic disk medium 1, a plurality of concentric tracks 3 centering on the center of rotation are formed. In the present embodiment, user data is recorded on a track defined by the concentric tracks 3. A servo sector 4 for detecting the position of the magnetic head 5 is recorded on each track 3.

  As shown in FIG. 2, the servo sector 4 includes a marker part M indicating the head of the sector, an AGC (Automatic Gain Control) part G, a track number T, and burst signals A to D for detecting the position between the tracks. Is done. Based on the information of the servo sector 4 read by the magnetic head 5, the position of the magnetic head 5 on the magnetic disk medium 1 can be detected at each sampling period Ts determined by the number of rotations of the SPM 2 and the number of sectors per track. .

  The magnetic head 5 is supported by a suspension 7 disposed at the tip of the carriage 6. A signal read from the magnetic disk device 1 by the magnetic head 5 is output to the head signal amplifier 9 via the flexible circuit 8. The magnetic head 5 records information on a magnetic disk medium based on a signal input from the head signal amplifier 9 via the flexible circuit 8.

  The carriage 6 is driven to rotate about the pivot by the VCM 11. As a result, the magnetic head 5 provided at the tip of the carriage 6 moves relative to the magnetic disk medium 1 to write and read the data.

  The head signal amplifier 9 amplifies the signal read by the magnetic head 5 and outputs the amplified signal to the modem 10. The head signal amplifier 9 amplifies the signal output from the modem 10 and outputs the amplified signal to the magnetic head 5.

  The modem 10 includes an analog / digital conversion circuit (A / D conversion circuit), converts the signal output from the head signal amplifier 9 into a digital signal, demodulates it, and outputs the demodulation result to the MPU 14. The modulator / demodulator 10 includes a digital / analog conversion circuit (D / A conversion circuit), modulates data to be recorded output from the MPU 14, further converts the data into an analog signal, and outputs a head signal. Output to the amplifier 9.

  The VCM 11 is controlled by a VCM drive signal input from the MPU 14. The MPU 14 controls the VCM 11 to move the magnetic head 5 to the position of a track to be read or recorded, and to make the magnetic head 5 follow the track. The VCM drive signal output from the MPU 14 is converted into an analog signal by the D / A conversion circuit 18, amplified by the drive amplifier 19, and output to the VCM 11.

  The MPU 14 operates according to a program stored in the storage unit 16. The storage unit 16 includes a RAM (Random Access Memory) 16a and a ROM (Read Only Memory) 16b. Here, the RAM 16 a also operates as a work memory of the MPU 14. The ROM 16b stores a program executed by the MPU 14 and the like. As a specific example, the MPU 14 controls the VCM 11 in accordance with a read or write instruction input from the host side, moves the magnetic head 5 to a desired track, and controls data read or write. Do. The process of controlling the VCM 11 will be described in detail later.

  The interface controller 20 receives data read from the magnetic disk medium 1 from the MPU 14 and outputs the data to the host-side controller 21. Further, the interface controller 20 outputs data output from the host-side controller 21 and instructions for reading and writing to the MPU 14.

  The host-side controller 21 is connected to a host-side device such as a personal computer. The host-side controller 21 outputs data output from the interface controller 20 to the host-side device. Further, data and instructions input from the host side device are output to the interface controller 20.

  Here, a process of controlling the VCM 11 by the MPU 14 will be described. Functionally, the control process of the VCM 11 executed by the MPU 14 of the present embodiment includes a follow-up control compensator 22, a periodic disturbance remover 23, a first adder 24, and a first adder 24, as shown in FIG. 2 adder 25. The periodic disturbance remover 23 includes a frequency generator 31, a frequency updater 32, and a filter 33.

  The tracking control compensator 22 receives a position error signal PES, which is the difference between the desired position and the actual position of the magnetic head 5, and suppresses the position error component over a relatively wide band, thereby controlling the entire control system. Generate a control signal to stabilize. The follow-up control compensator 22 can use a circuit that is widely known as a circuit that suppresses the non-periodic component of the position error, and thus detailed description thereof is omitted.

  Similar to the follow-up control compensator 22, the periodic disturbance remover 23 receives a position error signal PES that is a difference between a desired position and an actual position, and outputs it to the filter 33 and the frequency generator 31. To do. Here, the frequency generator 31 updates and outputs a state variable of a predetermined internal model (internal model) based on the position error signal PES.

  The frequency updater 32 outputs a frequency update signal ω (k) based on the state variable output from the frequency generator 31 and the position error signal PES. The filter 33 is a resonance filter (peak filter) that generates a signal having a specified frequency component. Here, based on the update signal ω (k) output from the frequency updater 32, the position error signal PES includes ω. A signal obtained by amplifying the frequency component of (k) is output. The filter 33 generates and outputs a signal having a phase opposite to the frequency component of ω (k) in the position error signal PES. This signal is a signal that generates a canceling force and a disturbance (physical external force that affects the position of the tip of the magnetic head 5) at the tip of the magnetic head 5.

  Here, the state variable of the internal model used by the frequency generator 31 can be used as the disturbance removal signal. However, in the present embodiment, a circuit (filter 33) that generates a disturbance removal signal is provided as a circuit different from this. Thereby, it is possible to stabilize the control system without reducing the convergence speed of the estimated frequency.

  The first adder 24 subtracts the actual head position signal detected by the magnetic head 5 from the reference position signal R representing the designated position, and outputs a position error signal PES.

  The second adder 25 adds the output signal of the tracking control compensator 22 and the signal output from the filter 33 of the periodic disturbance remover 23, and further outputs a signal for moving the magnetic head 5 to a desired position. These are added and output as a VCM drive signal for controlling the position of the magnetic head 5. Here, the output signal of the tracking control compensator 22 is a signal for moving the magnetic head 5 to a desired position, and the signal output by the filter 33 is for canceling the influence of disturbance on the tip position of the magnetic head 5. Signal.

  Next, a more detailed operation of the periodic disturbance remover 23 will be described. Here, description will be given first assuming an operation in a continuous system (a system in which values obtained by observation are values observed continuously in time).

と表すことができる。 That is, the arithmetic expression of the internal model in the frequency generator 31 is expressed as a first-order differential equation with respect to time using an arbitrary gain Kf and the frequency ω of the internal model.

It can be expressed as.

と選択できる。つまり、これらの状態変数は推定された外乱の成分と、その時間微分となる。このインターナルモデルは、L.J.Brown, Q.Zhang, "Periodic disturbance cancellation with uncertain frequency," Automatica, Vol.40, No.4, pp. 631-637, 2004 などで提案されているものである。 Assuming that the unknown disturbance is a single sine wave and other disturbances and noise can be ignored, the angular velocity of the disturbance is ωc and the input signal is
e (t) = A sin (ωc t)
State variables x1 (t) and x2 (t) are the system amplitude and phase at frequency ω, respectively, as B and θ, respectively.

Can be selected. That is, these state variables are the estimated disturbance components and their time derivatives. This internal model is proposed by LJBrown, Q. Zhang, “Periodic disturbance cancellation with uncertain frequency,” Automatica, Vol. 40, No. 4, pp. 631-637, 2004, and the like.

すなわち、

と表すことができる。このようにして外乱と、その周波数との関係が得られる。 From here, the relationship between the state variables x1 (t) and x2 (t) and the frequency ω

That is,

It can be expressed as. In this way, the relationship between the disturbance and its frequency is obtained.

を

として求める。この（５）式は、アークタンジェントの微分

から求められる。ここで、

とωとの差をεとすると、このεは（１）式を用いて、

と表すことができる。すなわち、本実施の形態では推定誤差が、外乱周波数の推定値とインターナルモデルの状態変数及び位置誤差信号によって表される。 Since ωc is unknown here, it is assumed that ωc is sufficiently close to the current frequency ω.

The

Asking. This equation (5) is the arctangent derivative

It is requested from. here,

If ε is the difference between ω and ω, this ε is calculated using equation (1):

It can be expressed as. That is, in this embodiment, the estimation error is represented by the estimated value of the disturbance frequency, the state variable of the internal model, and the position error signal.

を求めることが可能であるが、現実には、系には様々なノイズがあって、

を求めるだけでは意味がない。また、

は、ωcの近似値であるので、真の周波数ωcを求めるためには、

を時間積分して求めることとする。ここでＫｅは、収束の速度を定める任意の係数である。この時間積分により、ω＝ωcの平衡点が求められる。 Under ideal conditions, immediately from this error ε and the current frequency ω

In reality, there are various noises in the system,

It doesn't make sense to just ask. Also,

Is an approximate value of ωc, so to find the true frequency ωc,

Is obtained by time integration. Here, Ke is an arbitrary coefficient that determines the speed of convergence. By this time integration, an equilibrium point of ω = ωc is obtained.

  In a stable closed-loop system, when the change in frequency expressed by the equation (7) is sufficiently slow with respect to the dynamic behavior of the object to be controlled, that is, Ke is sufficiently small, and the initial value of ω is sufficient for ωc. When close (local), it is proved that ω is stable at the equilibrium point and converges exponentially.

  As described above, in this embodiment, the disturbance frequency itself is approximately obtained in the state space, and the error due to this approximation and other errors are converged to zero by the integrator that performs the time integration described above. Thus, it is different from the one that estimates the frequency of the disturbance indirectly by minimizing the positioning error.

The equation (7) has an equilibrium point not only at ω = ωc but also at ω = −ωc and ω = 0.
cos (−ωt) = cos (ωt)
Therefore, the equilibrium point of ω = −ωc is equivalent to the equilibrium point of ω = ωc. Further, when ω converges to the equilibrium point of ω = 0, ω may be initialized to a value other than zero.

であり、その係数は

と求めることができる。 Next, in order to process the above operation by a digital controller which is a discrete system, an operation which is discretized at a constant sampling period T will be shown. In this case, the difference equation corresponding to equation (1) is

And its coefficient is

It can be asked.

と、近似できる。 In addition, the differential equation for frequency update in equation (7) is expressed using Euler's equation,

And can be approximated.

となる。 Note that the MPU 14 performs the calculation with a finite word length, and therefore, the carryover of each variable may be reduced as much as possible. That is, in order to reduce the number of operations, ω (k) x1 (k) is newly redefined as x1 (k), the value of the product of Ke and Kf is redefined as Ke, and Ke is independent from Kf. Then, the state equation of the internal model and the differential equation of the frequency update are

It becomes.

となり、これにより、

として、ｘ1（ｋ）と、ｘ2（ｋ）とに関する独立した差分式を得ることができる。 Further, when the transfer function of equation (8) is obtained,

And this

As a result, an independent difference equation for x1 (k) and x2 (k) can be obtained.

と表わすことができる。ここでは、インターナルモデルの出力ｘ2（ｋ）をそのまま外乱除去信号として用いるのではなく、フィルタ３３を介して外乱除去を行わせている。このことで、（１４）式の分子（安定性に寄与する因子）を、好適な状態に定めることができる。すなわち周波数更新のためのゲインＫｅと、系の安定性のための係数ｂ１，ｂ２，ｂ０をそれぞれ独立に設計できる。このように調整パラメータを増加させることで、系全体の安定性を確保しつつ周波数更新の効率化を図ることが可能となる。 The transfer function of the filter 33 is

Can be expressed as Here, the output x2 (k) of the internal model is not used as it is as a disturbance removal signal, but disturbance removal is performed via the filter 33. By this, the molecule | numerator (factor which contributes to stability) of (14) Formula can be defined in a suitable state. That is, the gain Ke for updating the frequency and the coefficients b1, b2, b0 for system stability can be designed independently. By increasing the adjustment parameters in this way, it is possible to increase the efficiency of frequency update while ensuring the stability of the entire system.

  According to the present embodiment, the frequency generator 31 and the frequency updater 32 estimate the disturbance acting on the positioning of the magnetic head 5 using the servo signal read from the magnetic disk medium 1 by the magnetic head 5. This estimation is performed by an internal model, and the frequency generator 31 updates the estimated value using the previously estimated disturbance and a difference equation representing the time difference. The frequency updater 32 is initially set with an initial value of the estimated disturbance frequency.

  Then, the frequency updater 32 calculates an error (approximation error) between the estimated value and the frequency to be originally removed based on the estimated disturbance and the frequency, and the frequency is increased by an amount proportional to the calculated approximation error. Update the value. When the updated frequency becomes “0”, the frequency updater 32 resets the output frequency value to a predetermined value other than zero.

  The filter 33 extracts the signal of the center frequency component from the position error signal PES with the frequency signal output from the frequency updater 32 as the center frequency, and generates an amplified signal. This signal is added to the output signal of the follow-up control compensator 22 by the second adder 25 and is output as a VCM drive signal for controlling the position of the magnetic head 5.

  In such an update method, the initial value initially set for the frequency estimator 32 and the frequency of the signal to be removed included in the error signal, regardless of the difference between the frequency of the signal to be removed. The update width of the estimated frequency is controlled so that the convergence rate of the estimated frequency is constant.

  As described above, according to the present embodiment, it is possible to guarantee a constant convergence rate regardless of the setting of the initial value, suppress an increase in convergence time, and exhibit desired performance.

  In the magnetic disk device of the present embodiment configured as described above, an experimental example in the case where disturbances with frequencies of 300 Hz and 400 Hz are applied will be described. It is assumed that the estimated frequency ω is 150 Hz as an initial value of the estimated frequency. For comparison, an example in which a method of estimating the frequency of the disturbance indirectly by minimizing the positioning error without using the configuration of the present embodiment is also shown. First, FIG. 4 shows a frequency update situation and a position error signal convergence situation when the configuration of the present embodiment is not used.

  In FIG. 4, when the configuration of the present embodiment is not used, the convergence time increases and the convergence rate decreases as the difference between the initial value and the frequency of the signal to be removed increases. It is shown.

  FIG. 5 shows the frequency update status and the convergence rate of the position error signal when the configuration of the present embodiment is used. As apparent from FIG. 5, in the configuration of the present embodiment, the convergence rate (convergence time) of the estimated frequency and the convergence rate of the position error signal are both constant regardless of the difference between the disturbance frequency and the initial value. ing.

  FIG. 6 shows a graph in which the estimated frequency shown in FIGS. 4 and 5 is normalized by the difference between the disturbance frequency and the initial value of the estimated frequency. As is clear from FIG. 6, when the method of the present embodiment is not used, convergence becomes slower as the difference between the disturbance frequency and the frequency set as the initial value increases. When the method is used, it converges in substantially the same orbit regardless of the difference between the disturbance frequency and the initial value.

It is a schematic diagram showing the example of composition of the disk unit concerning an embodiment of the invention. It is explanatory drawing showing the example of the servo signal recorded on the disc apparatus concerning embodiment of this invention. It is a functional block diagram showing the structural example which positions the magnetic head of the disk apparatus based on embodiment of this invention. It is explanatory drawing showing the operation example of the magnetic disk which does not have the structure of this Embodiment based on a comparison with the disk apparatus based on the Example of this invention. It is explanatory drawing showing the operation example of the disc apparatus which concerns on the Example of this invention. It is explanatory drawing showing another example of operation | movement of the disc apparatus based on the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Magnetic disk medium, 2 Spindle motor, 5 Magnetic head, 6 Carriage, 7 Suspension, 8 Flexible circuit, 9 Head signal amplifier, 10 Modem / Demodulator, 11 Voice coil motor, 14 Microprocessor, 15 Bus line, 16 Memory | storage part, 18 Digital / analog conversion circuit, 19 driving amplifier, 20 interface controller, 21 host side controller, 22 tracking control compensator, 23 periodic disturbance remover, 24, 25 adder, 31 frequency generator, 32 frequency updater, 33 filter.

Claims (3)

A magnetic disk medium in which data is recorded along a predetermined trajectory;
A magnetic head that moves relative to the magnetic disk medium and writes and reads the data;
A position control circuit that receives an input of an error signal representing a position error of the magnetic head with respect to the predetermined trajectory, and controls the position of the magnetic head so that the magnetic head is positioned on the predetermined trajectory;
The position control circuit is
A frequency estimator that generates an estimated value of a disturbance frequency included in the error signal, and outputs the estimated value while updating the estimated value using the estimated value with respect to the frequency of the disturbance and a time change amount of the estimated value. A frequency estimator to
A disturbance remover for generating and outputting a signal having a phase opposite to that of the frequency component signal estimated by the frequency estimator, included in the error signal;
A magnetic disk drive comprising: The magnetic disk device according to claim 1,
The disturbance remover generates a disturbance removal signal by a circuit different from the operation in the frequency estimator, and is estimated by the frequency estimator included in the error signal based on the generated disturbance removal signal. A magnetic disk drive characterized by generating and outputting a signal having a phase opposite to that of the signal of the frequency component. A magnetic disk medium in which data is recorded along a predetermined trajectory;
A magnetic head that moves relative to the magnetic disk medium and writes and reads the data;
A position control circuit that receives an input of an error signal representing a position error of the magnetic head with respect to the predetermined trajectory, and controls the position of the magnetic head so that the magnetic head is positioned on the predetermined trajectory;
The position control circuit is
A frequency estimator for estimating a frequency of the error signal, initially setting an initial value and removing the signal regardless of a difference between the initial value and a frequency of a signal to be removed included in the error signal. A frequency estimator for controlling an update width of the estimated frequency so that a convergence rate of the estimated frequency with respect to a target signal frequency is constant;
A disturbance remover for generating and outputting a signal having a phase opposite to that of the frequency component signal estimated by the frequency estimator, included in the error signal;
A magnetic disk drive comprising:

Images