JP2655511B2 - 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 for reducing overshoot and undershoot of a head positioning servo system of a magnetic head.

[0002]

2. Description of the Related Art In a conventional magnetic disk drive, (1) a current-to-force conversion gain of a voice coil motor (VCM) used as an actuator for driving a head changes on the inner and outer circumferences of the disk; (2) Transient response at the time of head positioning is disturbed due to various factors such as the elastic force of the flexible cable for wiring (FPC) and (3) individual differences at the time of manufacturing the magnetic disk drive, and all tracks have the same characteristics. High-speed positioning cannot be performed. In recent years, digitization of a positioning control device has been advanced, and such a phenomenon has become a problem particularly in a system having a long sampling time.

Conventionally, several devices have been known to solve such a problem. For example, Japanese Patent Application Laid-Open No. 2-24
As disclosed in Japanese Patent No. 4467, a device for reducing the discontinuity of a digital filter internal variable at the time of control system switching by performing a part of the calculation of the position control system digital filter in parallel at the end of the speed control system. Or
JP-A-3-288913 and JP-A-4-335
As disclosed in Japanese Patent No. 272, there is an apparatus for resetting an initial value of a positioning control system when switching from a speed control system to a position control system.

[0004]

The above-mentioned conventional device is
An attempt was made to improve the transient characteristics by eliminating the discontinuity of the digital filter or minimizing the square integral of the state quantity of the controlled object. However, in the conventional apparatus, the transient response of the head positioning control system is not designed, or overshoot is performed in order to minimize the area integral value of the deviation of the state quantity between the fixed target and the control target from the switching point. In some cases, a solution that causes an overshoot or an undershoot may be obtained, and does not necessarily shorten the settling time required for head positioning.

An object of the present invention is to provide a magnetic disk drive capable of reducing the time required for positioning the magnetic head.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides one or more magnetic disks fixed on a rotating spindle, and reads and writes data from and to a data surface on the magnetic disks. Magnetic head, actuator for driving the magnetic head, drive amplifier for driving the actuator, head position detecting means for detecting the position of the magnetic head with respect to the data surface, and head for detecting the speed of the magnetic head Speed detecting means, and servo compensating means for controlling the drive amplifier so that the position of the magnetic head follows a target position, and obtains an eigenvalue and an eigenvector of the entire head positioning servo system of the magnetic head. From one eigenvector or a linear combination vector of the eigenvectors to the initial value state of the entire servo system. When a free response as a vector is used as a reference trajectory, an area error obtained by integrating the difference between the reference trajectory and the output signal of the servo system in a discrete time domain from an arbitrary state quantity of the control target is minimized. And an initial value setting means for initializing a part or all of the internal state of the servo compensation means.

[0007]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. As shown in FIG. 1, in a magnetic disk drive of the present invention, a composite head 106 as a magnetic head reads a signal recorded on a data surface 103 of a thin-film magnetic disk 102 fixed to a rotating spindle 101, A position error signal 109 is generated. The composite head 106 includes a thin-film inductive head for reading / writing data from / on the data surface on the magnetic disk 102 and an MR head.
(Magnetoresistive effect).

A servo head 105 reads a signal recorded on a servo surface 104 of a magnetic disk 102 fixed to the rotating spindle 101, and generates a servo head position error signal 110. The head position detecting device 111 includes:
Based on the data head position error signal 109 and the servo head position error signal 110, the number of times the servo head 105 has traversed the track including its direction is counted, and the position of the composite head 106 with respect to the data surface 103 is determined. The head position signal 1 is continuously detected from the innermost circumference to the outermost circumference of the magnetic disk 102 regardless of the traveling direction of the magnetic disk 102.
12 is generated. The head speed detection device 113 includes a head position signal 112 and an input signal 123 to the drive amplifier 108.
The head speed signal 114 is generated by detecting the speed of the composite head 106 with respect to the data surface 103.

[0010] The target trajectory generator 115 comprises a mathematical approximation model of the actuator 107 composed of one of a low-pass filter and a band-eliminated filter and a VCM. In consideration of the effect of the back electromotive force of the actuator 107, the output of the mathematical approximation model of the actuator 107 is used as the target trajectory signal 116 of the target position of the composite head 106, the target trajectory signal 117 of the target speed, and the target trajectory signal 118 of the target acceleration. Generate.

The feedforward compensator 119 generates an input signal 120 for driving the actuator 107 according to the target trajectory in advance using the target trajectory signal 118 of the target acceleration, and supplies the input signal 120 to the drive amplifier 108. The feedforward compensator 119 has a device for estimating the loop gain of the actuator 107, and adjusts the internal gain according to the individual difference of the disk device.

The servo compensator 121 is of a trajectory following type, and has a head position signal 112 and a head speed signal 11.
4 is an input signal 122 for following the target trajectory signal 116 of the target position and the target trajectory signal 117 of the target speed.
Is generated and given to the drive amplifier 108 to output the composite head 10
6 is performed. The servo compensator 121 has a device for estimating the loop gain of the actuator 107, and adjusts the internal gain according to the individual difference of the disk device.

The calculation delay is the time required from when the head position signal 112 is captured to when the input signal 123 to the drive amplifier 108 is generated. The initial value setting device 124 sets an initial value of the servo compensation device 121.

Next, the initial value setting device 124 will be described.

In this embodiment, the entire closed loop system of the control system having an operation delay of one sample is the head position signal 11
A case will be described in which an nth-order digital system is included as part of the internal state, including an input signal 123, which is 2, a head speed signal 114, and an operation delay state quantity. After setting the initial values, if the target trajectory signal 116 of the target position, the target trajectory signal 117 of the target speed, and the target trajectory signal 118 of the target acceleration are set to 0, the control including the head position signal 112, the head speed signal 114, and the servo compensator 121 is performed. The whole closed-loop state equation of the system is expressed by the following equation (1), and the output equation is expressed by the following equation (2).

[0016]

(Equation 1)

[0017]

(Equation 2) However, the internal state quantity X of the closed loop is expressed by the following equation (3).

[0018]

(Equation 3) At this time, the suffix c is the state quantity of the servo compensator 121, the suffix d is the state quantity of the operation delay, and the suffix p is the state quantity of the head position signal 112 and the head speed signal 114. As a state variable, the head position signal 112 is assigned to x _1, a head speed signal 114 is assigned to x _2. The state quantity that models the operation delay assigned to x _3. Further, the servo compensator 121 is, for example, a PID controller or the like, and can be variably set.
_4, x _5, ..., assigned to x _n. Also, in the following, a description will be given by taking the final equilibrium point of the n internal states as an example. However, even when the equilibrium point is not an example, a similar result is obtained by considering the difference between the non-zero equilibrium point and the internal state. Is obtained.

The eigenvalues of the system matrix A are obtained in advance, and among the eigenvalues, the eigenvalue of the fastest real root within a range that does not exceed the following characteristic of the actuator 107 is selected, and the eigenvector for the selected eigenvalue is obtained. Specifically, an eigenvalue near the control band of the servo system is selected, and an eigenvector corresponding to this eigenvalue is set as an initial value vector of the state of the closed loop system. Then, the eigenvector is converted to the head position signal 1
The coefficient corresponding to 12 is normalized so as to be 1, and n coefficients [1, c ₂ ,..., C _n ] are obtained in the same order as the n internal states. If there is no proper eigenvalue, n eigenvectors [v ₁ , v ₂ ,..., V _n ]
A vector that generates a response without overshoot or undershoot is obtained from the following equation (4), which is a linear combination of, and is set as an initial value vector of the state of the closed loop system.

[0020]

(Equation 4) Further, the vector v is normalized such that the coefficient corresponding to the head position signal 112 is 1, and is set to n coefficients [1, c ₂ ,..., C _n ] in the same order as the n internal states. .

Next, at the switching position x _r, n x (0) the internal state of the number _{= x r · [1, c} 2, ..., c n] and norms track number 5 of the following when the ^T .

[0022]

(Equation 5) Using this equation 5 as a reference trajectory, the response waveform from the position, speed, and operation delay state quantity [ _xr x ₂ (0) x ₃ (0)] ^T at the switching point follows the reference trajectory w (k). Thus, the internal state of the servo compensator 121 which can be reset is set. A method for setting the internal state of the servo compensator 121 will be described below.

The difference between the state quantity and the reference trajectory is given by η (k) = x
(K) −w (k), and the internal state J of the servo compensator 121 that minimizes the evaluation function of Expression 5 is obtained by Expression 6 below.

[0024]

(Equation 6) First, η _c , which is a function of the internal state of the servo compensator 121 that can be variably set, and the state amount of the head position signal 112 and the head speed signal 114 measured for performing the initial setting, the state amount of one sample operation delay A certain drive amplifier 1
08 is a function of the input signal 123 to η _pd = [η _p ^T
η _d ] ^T , and when Q is rewritten as a weight matrix in which all elements are non-negative, the following equation 7 is obtained.

[0025]

(Equation 7) Next, Expression 7 as an evaluation function becomes Expression 9 using Expression 8 which is a discrete-time Lyapunov equation.

[0026]

(Equation 8)

[0027]

(Equation 9) Further, Equation 9 which is an evaluation function is a quadratic function of the internal state of the servo compensator 121, and therefore Equation 9 has a minimum value and is minimum. Η _c (0) at which Equation 9 is minimized is expressed by Equation 10.

[0028]

(Equation 10) Therefore, the initial value of the servo compensator 121 that follows the reference trajectory w (k) is represented by the following equation (11).

[0029]

[Equation 11] The initial value setting device 124 calculates −p ₂₂ ⁻¹ · p ₁₂ and [1,
c ₂ ,..., c _n ] are stored in advance as a coefficient matrix.

Next, the initial value setting operation of the initial value setting device 124 will be described with reference to the flowchart of FIG.

The initial value setting device 124 first takes in the position signal 112 during the head positioning operation (step 2).
01). Subsequently, it is calculated whether the head position signal 112 has become smaller than an arbitrary value ε (step 202).
When the condition of step 202 is satisfied, the head speed signal 114 and the input signal 123 to the drive amplifier 108 are fetched (step 203), and the internal state quantity of the servo compensator 121 is obtained only once according to equation 11 (step 203). (Step 204), and output the initial value to the servo compensator 121 (Step 205).

By setting the initial value, the subsequent transient response of the control system can follow the reference trajectory obtained from the eigenvectors of the closed loop system. As a result, high-speed head positioning without overshoot or undershoot can be achieved. realizable.

FIG. 3 is a diagram showing a reference trajectory of a position referred to when setting an initial value according to the present invention. In FIG. 4, a curve A1 shows a transient response characteristic at the time of head positioning when an initial value is set to follow the reference trajectory according to the present invention, and a curve B1 shows a transient response at the time of head positioning without initial value compensation. The response characteristics are shown.

In order to obtain the transient response characteristics shown in FIG. 4, the initial head position is -5 μm and the head speed is 0.0
25 m / s. The input signal to the drive amplifier was 0.5 V. In the weight matrix in Equation 7, the value applied to the head position is set to 1, the value applied to the head speed is set to 10 ^-7, and the value applied to the drive amplifier 108 is set to 10 ^-11 . In the example of the curve B1 in which the initial state is not set and the internal state of the servo compensator 121 is set to zero, overshoot occurs.
In the example of the curve A1 according to the present invention, almost no overshoot or vibration occurs, and the settling time required for the head positioning of the magnetic head is reduced to about １ ／.

Even when individual differences or aging of the magnetic disk device exist, the internal gain adjustment by the loop gain estimating device of the servo compensator 121 and the feedforward compensator 119 can be performed to obtain the magnetic disk according to the present invention. The apparatus can realize high-speed head positioning without overshoot or undershoot.

Further, when the operation delay can be ignored, X _d is removed from the state quantity of the equation (3). X _p was added with internal state of the mechanical vibration removing device, overshoot or undershoot by the initial value setting unit 124 is not fast head positioning can be realized in.

[0037]

According to the present invention, in the conventional magnetic disk drive, the initial value setting which has not been determined in advance in consideration of the closed loop characteristics of the control system can be changed to an initial value for following the closed loop eigenvector at an arbitrary switching point. By setting the value, the vibration component can be removed from the transient characteristics, so that the time required for head positioning of the magnetic head can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of setting an initial value in the embodiment of FIG. 1;

FIG. 3 is a diagram showing a reference trajectory of a position referred to when performing initial value setting according to the present invention.

FIG. 4 is a diagram for explaining a transient response characteristic at the time of head positioning according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 101 rotating spindle 102 magnetic disk 103 data surface 104 servo surface 105 servo head 106 composite head 107 actuator 108 drive amplifier 109 data head position error signal 110 servo head position error signal 111 head position detecting device 112 head position signal 113 head speed detecting device 114 Head speed signal 115 Target trajectory generator 116 Target trajectory signal of target position 117 Target trajectory signal of target speed 118 Target trajectory signal of target acceleration 119 Feedforward compensator 120 Input signal to drive amplifier 108 121 Servo compensator 122 Drive amplifier 108 Input signal 123 to the drive amplifier 108 input signal 124 initial value setting device 125 initial setting value

Claims (2)

(57) [Claims] 1. A magnetic disk fixed on a rotating spindle, one or more magnetic disks, a magnetic head for reading and writing data from and on a data surface on the magnetic disk, an actuator for driving the magnetic head, and the actuator A drive amplifier for driving the magnetic head, a head position detecting means for detecting a position of the magnetic head with respect to the data surface, a head speed detecting means for detecting a speed of the magnetic head, and a position of the magnetic head following a target position. Servo compensating means for controlling the drive amplifier so as to determine the eigenvalues and eigenvectors of the entire head positioning servo system of the magnetic head. When the free response as the initial state vector of A part or all of the internal state of the servo compensating means is adjusted so that an area error obtained by integrating a difference between the reference trajectory and the output signal of the servo system in a discrete time domain from an arbitrary state quantity of the object is minimized. A magnetic disk drive comprising an initial value setting means for initializing. 2. The magnetic disk drive according to claim 1, wherein a head position signal indicating the position of the magnetic head and a head speed signal indicating the speed of the magnetic head are included as part x ₁ and x ₂ of the internal state. Based on the eigenvectors of the entire closed-loop system of the n-th order control system, a response without overshoot or undershoot is set as a reference trajectory, and the initial state quantity at this time is normalized with respect to the head position signal and n [1, c ₂ , ..., in the same order as the internal state
c _n ], and the initial value setting means stores the head position signal, the head speed signal, and the drive amplifier when the initial value setting position is reached during the head positioning operation of the magnetic head. A magnetic disk drive, wherein an internal signal of the servo compensating means is set to a value that minimizes an area error from a reference trajectory.