JP2861938B2 - Head positioning servo method for magnetic disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk drive, and more particularly to a servo control system for positioning a head in a magnetic disk drive.

2. Description of the Related Art In a magnetic disk drive, a head positioning servo control for a seek operation for positioning a head on a desired track is performed in an initial operation.

[0003] In the head positioning servo system of a magnetic disk drive, the dispersion of response waveforms due to external force, environmental changes, individual differences, etc. is suppressed, overshoot and undershoot during settling are improved, and the settling time is reduced. It is necessary to shorten it.

[0004]

2. Description of the Related Art In a magnetic disk drive, digitization of a positioning control device has been advanced. Particularly, in a system having a long sampling time, a servo compensator is not always provided with a sufficiently wide band. Has become a problem. As a method of shortening the seek time by improving the settling characteristic in the digital system, a method of appropriately resetting the internal state of the digital controller when switching from the seek operation to the follow operation is used.

For example, Japanese Patent Application Laid-Open No. 2-244467 discloses that at the end of the speed control system, a part of the calculation of the digital filter of the position control system is processed in parallel so that the internal variables of the digital filter when the control system is switched are not changed. Techniques for reducing continuity and improving transient characteristics are described.

[0006] Also, in Japanese Patent Application Laid-Open Nos. 3-288913 and 4-335272, when switching from the speed control system to the position control system, the state quantity of the positioning control system is determined by the difference from the steady state. A technique for resetting the evaluation value to a minimum and improving the transient characteristics is described.

Furthermore, Japanese Patent Application No. 7-58962 (Japanese Patent Application Laid-Open No. 8-255502) and Japanese Patent Application No. 7-67955 (Japanese Patent Application Laid-Open No. 8-273313) evaluate the difference between a reference trajectory and a position signal. A technique for shortening the settling time by a trajectory-following initial value compensation method that minimizes the value as a value is described.

FIG. 8 is a block diagram showing a basic configuration example of a conventional head positioning servo system of a magnetic disk drive to which the present invention is applied. FIG. 9 is similar to FIG.
FIG. 13 is a block diagram showing a configuration example in the case where a track following initial value compensation mechanism is added to the servo system of FIG.

In FIG. 8, a servo compensator 1 stabilizes a head positioning servo system and generates a servo compensator output 10 such that a head 5 moving on a rotating disk 4 follows a target trajectory 9. . This compensator output 10
Are amplified by the amplifier 2 and input to the actuator 3 to move the head 5. The head position on the disk surface is detected by a head position detector 6 and input to the servo compensator 1 as a head position signal 8.

FIG. 9 is a block diagram showing a servo system to which a trajectory-following type initial value compensation mechanism is added to the servo system shown in FIG. 1 shows an example of a servo system to which a trajectory tracking type initial value compensation method described in Japanese Patent No. 58962 is applied. By the head velocity signal 14 which is estimated by the head position signal 8 and the speed estimator 12, when it becomes less than a certain value the head position error in the trajectory tracking type initial value setting mechanism 13, a servo compensator 1 internal state x _c Reset.

FIG. 10 is a diagram showing the effect of improving response characteristics by the trajectory tracking type initial value compensation method. For a servo system which cannot obtain a sufficiently wide band and shows the response waveform 17 of FIG. 10 during settling, the initial value setting mechanism 13 of FIG.
By designing using the method described in Japanese Patent Application Laid-Open No. 58962/1995 or Japanese Patent Application Laid-Open No. 7-67955, it is possible to achieve a head response waveform 18 that follows the reference trajectory 16 in FIG.

On the other hand, a transient response at the time of head positioning may be disturbed by various factors, and it is not always possible to perform high-speed positioning with the same characteristics for all tracks.

[0013] Such factors include the following. 1) A change in the current-to-force conversion gain of a voice coil motor (VCM) used as an actuator for driving the head varies between the inner and outer circumferences of the disk. 2) The elastic force of the flexible wiring cable (FPC) works. 3) Individual differences at the time of manufacturing the magnetic disk device.

As means for estimating and canceling the magnitude of these external forces, external force compensators such as a robust compensator and a disturbance observer are used. For example, 1986, Comptrol; Vol. Pages 13, 53 to 58 describe a technique called robust model matching that improves only the frequency characteristic from an external force without changing the transfer characteristic from the target value of the control system to the control amount.

In the application of a disturbance observer to a magnetic disk drive, for example, in 1994, Transactions of the Society of Instrument and Control Engineers, Vol 1.30, No. 7, pp. 828-835, a disturbance observer is used to follow from a seek operation. A technique for reducing variation in switching to operation is described.

[0016]

The first problem in the prior art is as follows.
The problem is that in the trajectory-following initial value compensation method, a response waveform close to the reference trajectory can be achieved when the dispersion is small and the influence of external force is small, but the difference in target track position, environmental change, and individual difference For example, the magnitude of the external force is not constant. Even if an initial value for minimizing the evaluation value is set, settling without overshoot or undershoot is not necessarily obtained, and the settling time is not shortened.

A second problem in the prior art is that the response waveform improved by the external force compensator is a response waveform without external force. For this reason, in a control system with an external force compensator, it is necessary to design the controller so that the response waveform has no overshoot or undershoot. Is limited, and a method for improving the nominal waveform under long samples is required.

An object of the present invention is to solve such a problem of the prior art. In a magnetic disk drive, an external force suppressor reduces the effect of the deterioration of settling characteristics due to an external force. It is an object of the present invention to set an initial value to follow a reference trajectory at a switching point, to remove an overshoot and a vibration component from a settling characteristic, and to reduce a time required for positioning.

[0019]

SUMMARY OF THE INVENTION An external force applied to a head positioning mechanism is estimated and removed by adding an external force suppressor to a head positioning servo system for setting an initial value.
Thus, the apparent external force is reduced, and the internal state of the servo compensator is reset by setting the trajectory following type initial value, thereby improving the settling characteristics and speeding up the seek operation.

Hereinafter, specific means for solving the problems of the present invention will be described.

(1) A magnetic head (hereinafter simply referred to as a head) 5 for reading from and writing to the data surface of the magnetic disk 4
And an actuator 3 for moving the head 5 in the radial direction of the magnetic disk 4, an amplifier 2 for driving the actuator 3, and a head position detector 6 for detecting the position of the head 5 on the data surface. 7
On the other hand, by driving the amplifier 2 in accordance with the error between the detected head position and the target trajectory 9, the head positioning of the magnetic disk drive including the servo compensator 1 for causing the head 5 to follow the target trajectory 9 is performed. In the servo system,
Based on the position and speed of the head 5, some or all of the internal state of the servo compensator 1 is initialized so as to minimize the evaluation function consisting of the difference between the reference trajectory of the position or speed of the head 5 and the head position or speed. Orbit follower type initial value setting mechanism 23, and an external force suppressor for estimating an external force applied to the head 5 from the position of the head 5 and the input of the amplifier 2 and applying a signal to the input of the amplifier 2 to cancel the external force. 24
Are provided.

(2) In the case of (1), the external force correction table 35
By adding the external force correction table value 36 to the input of the amplifier 2, the effect of the external force on the head position is corrected.

(3) In the case of (1) or (2), the servo compensator 38 performs the following operation with the head position 8 and the head speed 14 as inputs.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to a positioning servo mechanism capable of observing the position and speed of a head. In such a servo mechanism, when the deviation value between the head position and the target position becomes smaller than an arbitrary external force compensator operation start value, the external force compensator is operated, and thereafter, the deviation between the head position and the target position. However, at the switching position that is smaller than the arbitrary initial value setting start value, the evaluation function consisting of the difference between the reference trajectory of the position or speed arbitrarily set independently of the feedback characteristics and the head position or head speed is minimized. So that the internal state of the digital controller is initialized.

First, the head positioning servo system shown in FIG. 9 will be discussed. In this configuration example, a case will be described in which the closed-loop system of the entire head positioning servo system is an n-order digital system including the head position signal 8, the head speed signal 14, and the servo compensator 1 . After setting the initial value, if the target trajectory 9 is set to 0, the head position signal 8
The closed loop state equation of the entire control system including the head speed signal 14 and the servo compensator 1 is expressed by equation (1), and the output equation is expressed by equation (2).

X (k + 1) = A · X (k) (1) y (k) = C · X (k) (2) where A is a system matrix (n × n), and C is an output matrix (N × m). However, the internal state quantity of the closed loop is
It is shown by the following equation (3).

[0027]

(Equation 2)

At this time, the suffix c is the state quantity of the servo compensator, and the suffix p is the state quantity of the head position and the head speed. As a state variable, the head position signal 8 to x _1, a head velocity signal 14 assigned to x _2. Further, the servo compensation means is, for example, a PID controller or the like and can be variably set.
This state variable is assigned to x ₃ , x ₄ ,..., X _n .

In the following description, the final equilibrium point of n internal states will be described as zero. However, when the equilibrium point is not zero, the difference between the non-zero equilibrium point and the internal state is considered. And similar results are obtained.

Next, at the initial value setting start position _xr ,
When n internal states are x (0), initial value setting is started with w (k) = ^AK × x (0) (k = 0, 1,..., m) (4) as a reference trajectory. head position at the position, the head _{speed, [x r x 2 (0} )] the response waveform from ^T, which can be reconfigured to follow the norm trajectory w (k),
The internal state of the servo compensator 1 is set. Hereinafter, a method for setting the internal state of the servo compensator 1 will be described.

The difference between the state quantity and the reference trajectory is given by η (k) = x
(K) -w (k), and the internal state of the servo compensator 1 that minimizes the evaluation function of the equation (4) is obtained.

[0032]

(Equation 3)

Where η (k + 1) = A · η (k) (k = 0, 1,..., N) (6)

First, η _c , which is a function of the internal state of the servo compensator 1 that can be variably set, and the state quantity η of the head position signal 8 and the head speed signal 14 measured for initial setting.
_{If p} is divided into _pd and Q is a weight matrix in which all elements are non-negative, equation (5) is rewritten as equation (7).

[0035]

(Equation 4)

Next, the evaluation function, Equation (7), becomes Equation (9) using the discrete time Lyapunov equation, Equation (8). A ^T・ P ・ A−P = −Q (8)

[0037]

(Equation 5)

Further, since the evaluation function, equation (9), is a quadratic function of the internal state of the servo compensator 1, equation (9) has a minimum value and is minimum. Η _c (0) at which Expression (9) is minimized is Expression (10).

[0039]

(Equation 6)

Therefore, the initial value of the servo compensator 1 that follows the reference trajectory w (k) is given by equation (11).

[0041]

(Equation 7)

Where w (0) = x _r · [1c ₂ ... C _n ] ^T (12)

As a result, as shown in FIG. 10, the head response waveform 17 which causes an overshoot from the target track center follows the reference trajectory of the waveform 16 by such a trajectory-following type initial value setting. To be improved.

FIG. 11 shows the positional relationship of the cylinders on the disk surface, as viewed from above the disk surface. The magnitude of the external force applied to the head positioning mechanism changes depending on where the target cylinder 19 of a certain seek is located from the outermost circumference to the innermost circumference.

FIG. 12 is a diagram showing the relationship between the cylinder position and the external force applied to the head positioning mechanism, and shows the change in the external force 21 applied to the head positioning mechanism with respect to the position of the target cylinder 19. As shown in FIG. 12, as a result of the change of the external force, the head position and the head speed at the time of setting the initial value have variations when the target cylinder and the moving seek distance are different.

FIG. 13 shows variations in the head position and the head speed at the start of the initial value setting due to the target cylinder difference and the moving seek length difference. For this reason, in the servo system in which the initial value is not set, the head position signal waveform changes, and the settling time deteriorates.

FIG. 14 is a block diagram showing a head positioning servo system to which an external force is applied, and shows a servo system in which initial values are not set. FIG. 15 shows an example of the deterioration of the response waveform due to the external force applied to the servo system shown in FIG.
However, the waveform changes from the waveform 17 to the waveform 22, and the settling time deteriorates as indicated by 23.

When the variation shown in FIG. 13 and the external force shown in FIG. 12 are small to some extent, only the initial value setting method can realize a small overshoot and a short settling time characteristic. And external force is large,
As shown in FIG. 15, the servo system whose settling time has deteriorated may not be sufficiently improved.

In the present invention, the disturbance of the waveform due to the external force is reduced by the external force suppressor, and the settling characteristic is improved by the trajectory following type initial value setting mechanism.

FIG. 1 shows an embodiment (1) of the present invention, and shows a servo control system to which an orbit-following type initial value setting mechanism and an external force suppressing mechanism are added. An external force suppressor 24 estimates an external force applied to the head from an input to the amplifier 2 and the head position signal 8, and generates an external force suppressor output signal 28 for canceling the external force applied to the head. Reference numeral 25 denotes an external force correction start determination mechanism, which outputs a signal 29 for determining the start of external force correction by the external force suppressor 24. Reference numeral 26 denotes an external force suppressor output on / off switch which is operated by an external force correction start determination signal 29 to control the addition of the external force suppressor output signal 28 to the servo compensator output signal 10,
As a result, a head positioning mechanism input signal (amplifier input signal) 27 is generated.

In the present invention, as shown in the block diagram of FIG. 1, after the disturbance of the waveform due to the external force is reduced by the external force suppressor 24, the trajectory following type initial value setting mechanism 13
Improves settling characteristics.

When the head positioning mechanism input signal 27 is u,
Let the head position 8 be y and let the transfer function from u to y be

[0053]

(Equation 8)

Assume that Further, the external force signal 16 is set to d, and the transfer function up to the head position 8 is

[0055]

(Equation 9)

Then,

[0057]

(Equation 10)

Can be expressed as follows.

As an example of an external force suppressor, a low-pass filter F for performing zeroing is added to the external force suppressor to obtain a signal

[0060]

[Equation 11]

Is the output 28 of the external force suppressor. This output 2
8 is added to the servo compensator output 10 only when necessary by the external force correction start determination mechanism 25.

FIG. 2 shows the effect of improving the settling characteristic by removing the influence of external force as shown in FIG. 13 by the servo system shown in FIG. It is shown that the settling characteristic 18 disturbed by the external force can be improved to a response waveform 30 that follows the reference trajectory 12 by combining the external force suppressor 24 with the settling characteristic 18.

When the head positioning servo system has an external force correction table, the use environment may change due to individual differences.

FIG. 3 shows an example of a change in the external force value due to individual differences. When the head positioning servo system has an external force correction table, the external force value 32 may change from the table value 31 due to individual differences, as shown in FIG.

FIG. 4 shows an example of a change in the external force value accompanying a change in the device temperature. When the head positioning servo system has an external force correction table, as shown in FIG.
The external force value 33 may change with respect to the table value 31 due to a temperature change.

FIG. 5 is a diagram showing a difference between the external force table reference value and the external force value, and shows an error 34 between the external force table reference value and the external force value when the external force value changes.

FIG. 6 shows the embodiment (2) of the present invention, and shows an example in which the present invention is applied to a servo control system having an external force correction table.

In FIG. 6, reference numeral 35 denotes an external force correction table (d _tbl ). By adding the output 36 to the amplifier input signal 27 of the head positioning mechanism 7, the settling characteristic deterioration due to the influence of the error 34 is improved. be able to.

In some cases, the servo compensator 1 operates using not only the head position 8 but also the head speed 14 as an input. Even in such a servo system, when there is a change in the external force value due to individual differences or the like, the deterioration of settling characteristics can be improved by adding an external force correction table.

FIG. 7 shows an embodiment (3) of the present invention, and shows an example in which the present invention is applied to a servo compensator for performing speed feedback.

In FIG. 7, the servo compensator 38 includes not only the head position determined by the state quantity 15 of the servo compensator reset by the trajectory tracking type initial value setting from the trajectory tracking type initial value setting mechanism 13, but also A head speed signal 14 from the speed estimating mechanism 12 is also input and an output signal 1
In this case as well, the external force correction table 35 is added, and the output 36 is added to the amplifier input signal 37 of the head positioning mechanism 7 to improve the settling characteristic deterioration due to the influence of the error 34. be able to.

[0072]

As described above, according to the present invention, the external force applied to the head positioning mechanism is estimated and removed by adding an external force suppressor to the head positioning servo system for setting the initial value. After reducing the above external force, the internal state of the servo compensator is reset by the trajectory-following initial value setting mechanism, so the settling characteristics can be improved and the seek operation can be speeded up. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment (1) of the present invention.

FIG. 2 is a diagram showing an effect of improving settling characteristics by removing an influence of an external force as shown in FIG. 13 by the servo system shown in FIG. 1;

FIG. 3 is a diagram illustrating an example of a change in an external force value due to an individual difference.

FIG. 4 is a diagram illustrating an example of a change in an external force value according to a change in device temperature.

FIG. 5 is a diagram illustrating a difference between an external force table reference value and an external force value.

FIG. 6 is a diagram showing an embodiment (2) of the present invention.

FIG. 7 is a diagram showing an embodiment (3) of the present invention.

FIG. 8 is a block diagram showing a basic configuration example of a conventional head positioning servo system of a magnetic disk drive to which the present invention is applied.

9 is a block diagram showing a configuration example in a case where a trajectory following initial value compensation mechanism is added to the servo system of FIG. 8;

FIG. 10 is a diagram showing the effect of improving response characteristics by the trajectory tracking type initial value compensation method.

FIG. 11 is a diagram showing a positional relationship of cylinders on a disk surface.

FIG. 12 is a diagram showing a relationship between a cylinder position and an external force value applied to a head positioning mechanism.

FIG. 13 is a diagram showing variations in head position and head speed at the start of initial value setting, due to a target cylinder difference and a movement seek length difference.

FIG. 14 is a block diagram showing a head positioning servo system to which an external force is applied.

FIG. 15 is a diagram illustrating an example of deterioration of a response waveform due to an external force applied to the servo system illustrated in FIG. 14;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Servo compensator 2 Amplifier 3 Actuator 4 Magnetic disk 5 Magnetic head 6 Head position detector 7 Head positioning mechanism part 8 Head position signal 9 Target trajectory 10 Servo compensator output signal 11 Amplifier output signal 12 Speed estimation mechanism 13 Initial value setting mechanism 14 Head speed signal 15 State quantity of servo compensator reset by trajectory tracking type initial value setting 16 Reference trajectory 17 Settling waveform without trajectory tracking type initial value setting 18 When trajectory tracking type initial value setting Settling waveform of 19 Cylinder 20 External force applied to head positioning mechanism 21 External force at each cylinder position 22 Settling waveform when external force of FIG. 12 is applied to servo system of FIG. 14 23 Settling time deterioration 24 External force suppressor 25 External force correction start judgment mechanism 26 External force suppressor output n / off switch 27 Amplifier input signal 28 External force suppressor output signal 29 External force correction start determination signal 30 Servo settling waveform when initial value is set in FIG. 1 31 External force correction table value 32 External force value due to individual difference 33 External force value after temperature change 34 Error between external force correction table value and external force value 35 External force correction table 36 External force correction table value 37 Amplifier input signal 38 Servo compensator at speed feedback

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-265079 (JP, A) JP-A-2-89264 (JP, A) JP-A-2-232875 (JP, A) JP-A-4- 232676 (JP, A) JP-A-59-117759 (JP, A) JP-A-57-82257 (JP, A) JP-A-63-9083 (JP, A) JP-A-3-30156 (JP, A) JP-A-4-40677 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 21/10

Claims (3)

(57) [Claims] A magnetic head for reading and writing data on a data surface of a magnetic disk (hereinafter, simply referred to as a head); an actuator for moving the head in a radial direction of the magnetic disk; an amplifier for driving the actuator; By driving the amplifier in accordance with an error between the detected head position and a target trajectory, the head is moved to a head positioning mechanism unit including a head position detector that detects a position on a data surface of the head. In a head positioning servo system of a magnetic disk drive including a servo compensator for following a target trajectory, the head position and speed include a difference between a reference trajectory of the position or speed of the head and the head position or speed. so as to minimize the evaluation function shown by the following formula (7), the internal state of the servo compensator A trajectory-following type initial value setting mechanism for initializing a part or the whole; and estimating an external force applied to the head from the position of the head and the input of the amplifier, and applying a signal for canceling the external force to the input of the amplifier. A head positioning servo system for a magnetic disk drive, comprising an external force suppressor. (Equation 1) However, η _c is variably set inside the servo compensator.
A function of state, η _pd is measured to make the initialization
State quantity of the head position signal and the head speed signal, q _pd
Is the weight of the head position signal and the head speed signal
T is a symbol representing the transposition of a vector. 2. The head positioning servo system for a magnetic disk drive according to claim 1, further comprising an external force correction table, wherein the external force correction table value is added to an input of said amplifier, so that an influence of the external force on said head position is reduced. A head positioning servo method for a magnetic disk drive, wherein the correction is performed. 3. The magnetic disk drive according to claim 1, wherein the servo compensator performs the following operation by inputting a head position and a head speed. Head positioning servo system for the device.