JPH09306125A - Servo system for magnetic disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce variation in speed control and to shorten a seeking time in a control system of a seeking operation in a servo system of a magnetic disk device. SOLUTION: In the magnetic disk device capable of performing the seeking operation by digital sampling control, a position and a speed of a servo head ahead of one sample are estimated by a state observation unit 23 from position information of a servo head and current information of a voice-coil motor, while a seeking current calculating means 47 is provided, and a current value of the next period is successively calculated in order to make a position and a speed ahead of two samples from the estimated position and speed asymptotic to an orbit of the position to the speed given from a speed orbit table 42. By repeating the successive calculation until the time when a difference between an estimated speed in a position ahead of two samples by this current value and an orbit speed falls within a preset error or the reach a predetermined number of times of calculation, a current value of the voice-coil motor 4 is decided to perform the seeking operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo system for a magnetic disk device, and more particularly to a seek operation control system for the magnetic disk device.

A magnetic disk device has a seek function of moving a magnetic head to a desired cylinder position on the disk surface by a servo system at the start of recording and reproducing operations.

In a servo system of a magnetic disk device, it is necessary to shorten the time (seek time) required to reach a desired cylinder during seek operation as much as possible.

[0004]

2. Description of the Related Art A servo system of a magnetic disk device has a function of moving a magnetic head to a desired cylinder position on the disk surface and holding the magnetic head on the center line of the cylinder. At this time, the operation of moving the magnetic head in cylinder units is called seek, and the operation of holding the position of the magnetic head at the position on the center line of the cylinder is called track follow.

In the conventional servo system of the magnetic disk device, the seek operation is feedforward control +
It was done in the form of feedback control. In this case, in feed-forward control, as a function of time,
Alternatively, a predetermined signal is added to the feedback signal as a function of the residual seek length. Further, in feedback control, as described in, for example, Japanese Patent Laid-Open No. 3-30153, there are many cases where feedback control is performed by multiplying the gain of the difference between the target speed and the estimated speed.
Alternatively, as described in, for example, Japanese Patent Application Laid-Open No. 58-194174, there is an example in which feed-packing is performed by multiplying the difference between the target position and the estimated position or the measured position by a gain.
That is, the seek operation is performed by performing the planned acceleration / deceleration assumed at the time of design by feedforward and correcting the error from the assumed trajectory by feedback.

FIG. 3 shows a general configuration of a servo system of a magnetic disk device. As a servo system of HDD (hard disk device), a servo surface servo that controls by using information of a dedicated servo surface in which only servo information is recorded, and servo information is embedded in a part of the data recording surface at regular time intervals. , There is a sector servo which performs control using sector information, but FIG. 3 assumes the case of a servo surface servo.

In FIG. 3, 1 is a disk plate, 2 is a servo amplifier, 3 is a head support system, 4 is a voice coil motor, 5 is a servo amplifier (power amplifier), 6 is a position information detection circuit, and 7 is a track crossing pulse. Detection circuit, 8 is a track counter, 9 is an AD converter (ADC), 10 is DA
A converter (DAC), 11 is a microprocessor means (M
PU) and 12 are position signals.

The servo head 2 reads the servo information recorded on the servo surface of the disk plate 1. The position information detection circuit 6 converts the read servo information into a position signal 12. Since the position signal 12 has a sine wave shape or a triangular wave shape when the servo head 2 moves, the track crossing pulse detection circuit 7 generates a track crossing pulse by comparing the position signal 12 with an appropriate voltage level. The track counter 8 counts track crossing pulses.

The microprocessor means 11 can know the number of moved tracks by reading the value of the track counter 8. Further, by reading the magnitude of the position signal 12 via the AD converter 9, the amount of displacement within one track from the center line of the track can be known. The microprocessor means 11 can recognize the position of the servo head 2 with high resolution by synthesizing both the value of the AD converter 9 and the value of the track counter 8.

In the case of the sector servo system, since the servo information cannot be obtained continuously, the track crossing pulse cannot be generated. Instead, since the track address is written as the servo information, the value corresponding to the value of the track counter 8 can be directly obtained by reading this address information. That is, except that an address decoder is used instead of the track crossing pulse detection circuit 7 and the track counter 8,
The method of servo control is the same, and the present invention can be applied to both servo surface servo and sector servo.

The microprocessor means 11 determines the voice coil motor to be controlled from the current (latest position information sampling time) and past position information of the servo head 2 and the information of the current value passed through the voice coil motor 4. The position and velocity of the servo head 2 at the next sampling time are estimated using the digital model.

This calculation method is known as a state observer or state estimator of control theory. The voice coil motor 4
Originally, the current value of
This is the result output to the DA converter 10, and the servo amplifier 5
Is normally configured as a current amp, and when the amp is not saturated, it can be calculated from the output value to the DA converter 10. However, when the amp is saturated, a circuit that outputs a current value is provided and the value is AD converter. Via 9 separate channels,
It must be incorporated into the microprocessor means 11. The output of the servo amplifier 5 is connected to the input of the AD converter 9 to indicate this current detection function.

FIG. 4 is a block diagram showing a control system in a servo system of a conventional magnetic disk device. In the figure, the servo amplifier 5 and the DA converter 10 are the same as in the case of FIG.

In FIG. 4, 21 is a controlled object, 22 is position detecting means, 23 is a state observer, 24 is a subtractor, and 25 is a subtracter.
Is the error feedback coefficient (Kf) of the state observer, 26
Is an AD converter (ADC). 27 is a head support system 3
An external force canceling value composed of a current value for canceling the external force applied to, 28 is a subtractor, and 29 is an adder. 30,
Reference numerals 31 and 34 denote the proportional coefficient Kp, the integral coefficient Ki, and the integral coefficient Ki, when performing the control known as PID control in the control theory.
It is the differential coefficient Kd.

Reference numeral 32 denotes a Z conversion storage element, and 33
Integrating operation is performed in combination with the adder shown in. 3
Reference numerals 5 and 35A denote adders, which are 3 for PID control.
Adds two control signals. A filter 36 limits the band of the signal in order to suppress the mechanical resonance of the controlled object. A delay element 37 corresponds to the time delay required for the microprocessor means 11 to perform the calculation. A switch 38 controls ON / OFF of the operation of the PID-controlled integrator.

The servo system has two operation modes, a track follow mode in which the servo head 2 follows the target track and a seek mode in which the servo head 2 is moved (seeked) to another track. ing.
Reference numeral 39 denotes a switch for switching the operation mode of the servo system. When the switch 39 is switched to the lower side of the drawing, the track follow mode is set and the position of the servo head 2 is controlled by PID control. .

In the track follow mode, 40
The result of multiplying the position error information Xe for the target (the center line of the track) from the state observer 23 by the proportional coefficient Kp shown by 30, and the speed estimation from the state observer 23 shown by 41 The value is multiplied by the differential coefficient Kd indicated by 34, and the position error information Xe indicated by 40 is integrated by the Z conversion storage element 32 and the adder 33. The position of the servo head 2 is controlled by PID control by applying a signal obtained by adding the result obtained by multiplying Ki by the adders 35 and 35A through the filter 6 for a period of time.

On the other hand, when the switch 39 is switched to the upper side, the seek mode is set, and the movement speed of the servo head 2 is controlled so that the servo head 2 is adjusted to the track. 42
Is a table (numerical table) storing velocity trajectories for the remaining seek distances to the target position.

The lower right part of FIG. 4 is a seek control section. The position error state X from the state observer 23 indicated by 40
From e (remaining distance to the target), velocity trajectory table 4
2 produces a target speed signal. Further, from this, the subtracter 43 multiplies the error obtained by subtracting the speed estimation value Vel from the state observer 23 shown by 41 by the coefficient Kv shown by 44 to determine the feedback amount.
On the other hand, 45 is a feed-forward unit, which is shown by 40 in accordance with the position error state Xe from the state observer 23.
A predetermined feedforward amount is output.
An adder 46 adds a feedback amount and a feedforward amount to generate a control amount in the seek mode.

[0020]

In a servo system of a magnetic disk device, in the case of a digital servo which performs position detection at a constant sampling cycle, information on an error from a target can be obtained discretely and only at discrete values. Therefore, the above-described conventional feedback method cannot smoothly reduce the error. Therefore,
There is a problem in that the response when reaching the target position tends to vibrate and the settling time is extended. In particular, when the sampling cycle is long, this tendency becomes remarkable, and the variation when the same seek operation is repeated becomes large.

In order to shorten the seek time,
Speed control for sudden acceleration and sudden deceleration is required, but with conventional feedforward + feedback control, individual H
If there are variations in DA (head / disk assembly) parameters, errors during rapid deceleration cannot be sufficiently absorbed, the speed at the arrival of the target track fluctuates, and it takes time to settle the position. .

The present invention is intended to solve such a problem of the prior art, and in a servo system of a magnetic disk device, it is possible to reduce variations in speed control during seek control. It is an object of the present invention to provide a new control method capable of shortening the seek time.

[0023]

In the servo system of the magnetic disk drive of the present invention, the future value of the residual seek length and the speed obtained by estimating and calculating the future value of the residual seek length and the speed in the digital servo system. The current value of the actuator (voice coil motor) is sequentially calculated so that the value relationship gradually approaches a preset trajectory pattern.

More specifically, in the digital servo system of the present invention, in the magnetic disk device, the position and velocity of one sample ahead are estimated from the position information of the head and the current information of the actuator by digital sampling control. Then, the current value in the next period is sequentially calculated so that the estimated values of the position and velocity two samples ahead are asymptotic to the position-to-velocity trajectory pattern. The current value of the actuator is calculated by repeating this sequential calculation until the error between the estimated velocity and the orbit velocity at the position two samples ahead falls within a preset error or the preset number of calculations is reached. It is determined and controlled so as to follow.

According to the method of the present invention, since the target trajectory is known in advance, by predicting the future position and speed and controlling the future control result to approach the trajectory, the current or past information is obtained. Compared with the conventional method that is controlled based only on the above, there is no control delay, and the deviation from the trajectory can be reduced as compared with the case of the conventional method.

Specific means for solving the problems of the present invention will be given below.

(1) In the magnetic disk device, the future values of the residual seek length and the velocity are estimated, and the relationship between the estimated residual seek length and the future value of the velocity is asymptotic to a preset trajectory pattern. As described above, the seek operation is performed by successively calculating and determining the current value of the voice coil motor 4 that drives the servo head 2.

(2) In a magnetic disk device which performs a seek operation of controlling the current of the voice coil motor 4 for driving the servo head 2 to move the servo head 2 to a predetermined cylinder position of the disk plate 1 by digital sampling control, From the position information of the servo head 2 and the current information of the voice coil motor 4, the state observer 23
The position and speed of the servo head 2 at the sample destination are estimated, and the seek current calculation means 47 is provided so that the position and speed at the second sample destination can be calculated from the estimated position and speed.
The current value for the next period is sequentially calculated so as to approach the position-to-speed trajectory given from the velocity-trajectory table 42, and the difference between the estimated velocity and the orbit velocity at the position two samples ahead is preset by this current value. The current value of the voice coil motor 4 is determined and the seek operation is performed by repeating the sequential calculation until the error is within the predetermined error or the predetermined number of calculations is reached.

(3) In the case of (2), the orbital velocity at the position moved by one sampling period at the estimated velocity of one sample ahead is obtained, and the current value required for a change of 1/2 of the velocity difference in this period is calculated. Then, the position and speed when this current is applied are calculated, and the current value required for a change of 1/2 of the speed difference from the speed on the orbit at this position is calculated. An asymptotic current value of the voice coil motor 4 is obtained.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention, and assumes servo surface servo as in the case of FIG. The same components as those in FIGS. 3 and 4 are denoted by the same reference numerals, and their functions and operations are similar to those in FIGS. 3 and 4, so detailed description thereof will be omitted below.

In the configuration of FIG. 1, the configuration and operation in the track follow mode are similar to those of the conventional circuit shown in FIG. Reference numeral 47 is a seek current calculation means, and 48 is a gain correction coefficient Ka.

The seek current calculation means 47 refers to the table (numerical table) in which the velocity trajectories for the remaining seek distances up to the target position in the velocity trajectory table 42 are stored, and is indicated by 40 from the state observer 23. The current value to be set in the next period is determined from the position error information Xe and the speed estimation value Vel from the state observer 23 indicated by 41. By multiplying this current value by a gain correction coefficient Ka indicated by 48, the filter 36, the delay element 37,
By correcting the gains of the adder 29, the DA converter 10, and the servo amplifier 5, the DC gain up to the servo amplifier 5 is set to 1
To

In FIG. 1, the DA converter 10, the servo amplifier 5, the controlled object 21, the position information detecting means 22,
The components other than the AD converter 26 can be realized by the calculation function of the microprocessor means 11 shown in FIG. The DA converter 10 and the servo amplifier 5 are the same as in the case of FIG. The controlled object 21 corresponds to the head support system 3 and the voice coil motor 4 shown in FIG. The position information detecting means 22 represents the combined function of the servo head 2, the position information detecting circuit 6, the track crossing pulse detecting circuit 7, the track counter 8 and the AD converter 9 shown in FIG. The AD converter 26 corresponds to one channel (for current value detection) of the AD converter 9 shown in FIG.

The seek operation of the present invention will be described below. FIG. 2 is a diagram for explaining the operation of the seek current calculation means 47, showing a trajectory curve and a seek current calculation procedure in the present invention.

In FIG. 2, the horizontal axis represents the remaining distance (remaining seek length) X to the target, and the vertical axis represents the velocity V. The curve in FIG. 2 shows the target velocity trajectory. The seek current calculation means 47 puts the position and speed one sample ahead on the target trajectory curve (or at that time) based on the distance Xe to the target and the speed estimation value Vel corresponding to that time at the latest sampling time. An electric current value that brings the state closer to each other is calculated with reference to the table (numerical table) of the velocity trajectory table 42.

An example of a concrete calculation procedure of the seek current calculation means 47 will be described below. The position (X1) and speed (V1) at the next sampling time are estimated from the current (current sampling time) position information and the voice coil current detection value (current sense). The relationship between the position and the speed is determined by the control performed in the past and can no longer be changed.

It is necessary to obtain the orbital velocity (V2) at the position X2 = X1-V1T which is advanced by one sampling cycle T with the velocity (V1) as it is, and to change the velocity by 1/2 of (V1-V2). Calculate the appropriate current value. The following equation shows the current calculation formula, which is derived from a simplified physical model. I1 = (V1-V2) / (2GT) (1) Here, G is the acceleration constant of the voice coil motor (VCM).

The position when this current is passed is as shown by the following equation. X3 = X1-V1T + (GT 2/2) · I1 ... (2) The speed at this time is as follows. V3 = V1- (GT) · I1 (3)

Next, the velocity V4 on the orbit at the position X3
And a current value for changing the speed by 1/2 of the speed difference (V3-V4) is calculated by the following equation. I2 = (V3-V4) / (2GT) (4)

Further, the position and velocity X5 and V5 when the current is applied (I1 + I2) are calculated, the velocity V6 on the orbit at X5 is calculated, and if the velocity difference (V5-V6) is not less than the specified value, the same is true. Repeat the calculation. If it is within the specified value, the current value obtained by the calculation up to that point is set as the final value, and the DA converter 10 is set to flow the current at the next current setting timing.

If the processing time exceeds the sampling cycle, the processing will not be in time and an error will occur. Therefore, the maximum number of repetitions is determined from the relationship between the calculation capacity and the sampling cycle. The number of calculation iterations is limited to a smaller number. The predicted position two steps ahead may be an intermediate value of the position values on the table of the position-to-speed trajectory, but the value of the velocity trajectory in that case is calculated by the polygonal line approximation.

The current value is determined by the above calculation method, but if the current value tends to vibrate, additional means such as adding a filter or limiting the amount of change from the previous current value is added. May be.

Further, the minimum current value candidate I of the iterative calculation is I.
As 1, the control current value by the conventional feedforward + speed feedback method may be used, or the feedforward value may be used.

[0044]

As a first effect of the present invention, the follow-up characteristic to the velocity trajectory in the seek operation is improved as compared with the conventional velocity feedback + feedforward control. This is because the feedforward control is either predetermined at the time of design or adjusted to some extent beforehand by learning, and cannot cope with the situation change during the seek that is currently being performed. This is because the feedback control can only be dealt with, but the feedback control does not predict and determine future changes in the trajectory, and can only improve the error by relying only on information that is already in the past.

As a second effect of the present invention, the variation in transient response at the end of seek is reduced. This is a natural result based on the improved tracking of the trajectory curve.

As a third effect of the present invention, since the follow-up characteristic is improved, the inclination of the deceleration curve (velocity trajectory) when approaching the target can be made steeper than in the past, and as a result, the seek time can be shortened. can do.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining the operation of a seek current calculation means.

FIG. 3 is a diagram showing a general configuration of a servo system of a magnetic disk device.

FIG. 4 is a block diagram showing a control system in a servo system of a conventional magnetic disk device.

[Explanation of symbols]

 1 disk board 2 servo head 3 head support system 4 voice coil motor 5 servo amplifier 6 position information detection circuit 7 track crossing pulse detection circuit 8 track counter 9 AD converter (ADC) 10 DA converter (DAC) 11 microprocessor means ( MPU) 12 Position signal 21 Controlled object 22 Position information detecting means 23 State observer 39 Switch 40 Position error information Xe 41 Velocity estimation value Vel 42 Velocity orbit table 47 Seek current calculation means 48 Gain correction coefficient Ka

Claims (3)

[Claims] 1. A magnetic disk device estimates future values of a residual seek length and a velocity, and makes the relationship between the estimated residual seek length and a future value of the velocity asymptotically approach a preset trajectory pattern. 2. A servo system for a magnetic disk drive, wherein the seek operation is performed by sequentially calculating the current value of a voice coil motor that drives the servo head. 2. A magnetic disk device for performing a seek operation of controlling a current of a voice coil motor for driving a servo head to move the servo head to a predetermined cylinder position of a disk plate by digital sampling control. The state observer estimates the position and velocity of the servo head one sample ahead from the position information and the current information of the voice coil motor, and a seek current calculation means is provided to obtain two samples from the estimated position and velocity. The current value in the next period is sequentially calculated so that the previous position and velocity are asymptotic to the position-to-velocity trajectory given from the velocity trajectory table, and the estimated velocity and the trajectory velocity at the position two samples ahead by the current value are calculated. Until the difference is within a preset error or a predetermined number of calculations is reached. By repeating the calculation, the servo system of a magnetic disk apparatus characterized by performing a seek operation defines the current value of the voice coil motor. 3. The servo system of the magnetic disk drive according to claim 2, wherein an orbital velocity at a position moved by one sampling period at the estimated velocity of one sample ahead is obtained, and the velocity difference of 1/2 of the velocity difference in the period is obtained. The current value necessary for the change is calculated, and the position and speed when the current is applied are calculated, and the speed difference between the position and the speed on the orbit at that position is 1
A servo system for a magnetic disk drive, characterized in that the current value of a voice coil motor asymptotic to the orbit is obtained by repeating a calculation for obtaining a current value required for a change of / 2.