JPH03122877A - Controller for magnetic disk device - Google Patents

Abstract

PURPOSE:To make a settling time required for leading in a target track short and to control over-shooting from the target track to be small by properly setting a cut-off frequency, a phase margin, a gain margin or the like. CONSTITUTION:A switching controller 8, a seeking controller 9, a settling controller 10, a following controller 11 or the like are included in a device and the digital filter 19 of the settling controller 10 serially connects primary phase- lead filters 17 for low-pass and for high-pass. Due to that, the respective filters 17 can properly select phase-lead. Besides, since the lower bent point of the high-pass filter is situated on the low frequency side of the upper bent point of the low-pass filter, the extent of the superposition can be properly selected. As a result, since the phase margin can be properly selected as a whole and the cut-off frequency, the gain margin and steady-state deviation can be properly selected at the same time, the degree of freedom of design for making a transit characteristic excellent is high. Thus, the settling time required for leading in the target track is made short and the over-shooting from the target track is checked.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention aims to improve magnetic heads in magnetic disk drives.
The present invention relates to a control device for settling control of pulling into a rack.

[Conventional technology]

The following three examples can be given as settling control methods in conventional control devices.

(1) Regarding a magnetic disk device that positions a magnetic head on a target track, for example, Japanese Patent Laid-Open No. 57-12455
There are some that are listed in the publication. According to this document, the magnetic head is comprised of seek control for moving the magnetic head to a target track, settling control for pulling the magnetic head into the target track, and following control for following the target track, and each control method is described. Among these, settling control uses a feedback signal for transient control created from a position signal and a speed signal. This is considered to be an attempt to improve the transient characteristics by aiming at the phase advance caused by the speed signal.

(2) Also, in Proceedings of the Ninth International Combination Onside Negotiations (1980), pp. 397-411,
There is a description of settling control. Here, in order to improve the transient characteristics of settling control and prevent overshoot 1, an integrator or a phase delay element is not used, and only a one-stage phase lead filter is used. After pulling into the target trunk through settling control, an integrator or phase delay element and phase advance filter are used.

(3) Also, 1981 IEICE General National Conference 1
554 (1981), pages 6-143, there is a description of a two-stage phase lead filter in which the same phase lead filter is doubled. Although this is described as being used for following control rather than settling control, it is presumed that residual vibration can be suppressed even when used for settling control since the phase lead can be large. .

[Problem to be solved by the invention]

The above conventional technology can also be applied to a control device for a magnetic disk drive that positions the magnetic head to a target trunk using a sector servo method, but each method has the following drawbacks and is not suitable as a settling control method. isn't it.

(1) In the sector servo method, position signals can only be obtained discretely. Therefore, when a speed signal is generated from now on, there will be a large time delay from the actual speed.

Therefore, good phase lead characteristics cannot be achieved by the feedback signal for transient control generated from the position signal and the speed signal. For this reason, excessive cl in settling control
There was a problem that the marking characteristics could not be improved.

(2) In the sector servo method, control operations are performed in discrete time, so the calculation time for determining the amount of operation is
A large phase delay occurs due to the delay time due to the manipulated variable being held between sectors. therefore,
In order to obtain a sufficient phase lead with a one-stage phase lead filter, it is necessary to widely separate the low-frequency break point and the high-frequency break point. However, since there is a sampling frequency determined by the sector interval, the high-frequency side bending point cannot be made unnecessarily high. In addition, steady-state deviation occurs due to the decrease in low-frequency gain, so
The low-frequency side bending point cannot be made unnecessarily low. Therefore, there was a problem in that the transient characteristics of settling control could not be improved.

(3) Compared to the one-stage phase lead filter, the two-stage phase lead filter can obtain a sufficient phase lead without having to separate the low-frequency break point and the high-frequency break point so widely. However, when this filter is used, there are only two design parameters, a low-frequency break point and a high-frequency break point, so there is less freedom in designing to improve transient characteristics. Furthermore, if the range of phase lead is widened, the phase margin increases, but the gain margin decreases, so the cutoff frequency changes with a slight change in physical parameters. From these points of view, there was a problem in that the transient characteristics of settling control could not be improved as much as expected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device comprising a filter that has a high degree of freedom in design and has good transient characteristics as a filter for settling control of a sector servo type magnetic disk drive.

[Means to solve the problem]

In order to achieve the above object, a magnetic disk control device includes seek control for moving the magnetic head to the target 1-rack using a sector servo method, settling control for pulling the magnetic head into the target track, and following control for causing the magnetic head to follow the target track. In the above, the digital filter for settling control is a combination of first-order phase advance filters for low-pass and high-pass in series, and the lower bend of the high-pass filter is placed on the low frequency side of the upper bend of the low-pass filter. It was designed so that the points would arrive.

[Effect]

In the magnetic disk drive control device of the present invention, since the digital filter for settling control is a combination of a low-frequency first-order phase lead filter and a high-frequency first-order phase lead filter in series, the phase lead can be appropriately selected for each. Further, since the lower bending point of the high-pass filter is on the low frequency side of the upper bending point of the low-pass filter, the degree of overlap can be appropriately selected.

This allows the overall phase margin to be appropriately selected. At this time, the cutoff frequency is also set.

Since the gain margin and steady-state deviation can be appropriately selected, there is a large degree of freedom in design for achieving good transient characteristics. As a result, the settling time for pulling into the 1'' mark track can be shortened, overshoot from the target trunk can be suppressed, and the transient characteristics of settling can be improved.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the overall configuration of a magnetic disk device to which the present invention is applied. Reference numeral 1 designates a disk disk for magnetic recording, and each surface is divided into a plurality of fan-shaped sectors 2 at equal intervals for recording data signals. A sector servo signal portion 3 is provided at the boundary of the sector, in which a sector servo signal consisting of a track number and a position signal for positioning the magnetic head 4 at a specific position in the radial direction of the disk is recorded in advance. This disk l is rotated at a constant rotation speed by a spindle motor (not shown). A magnetic head 4 is provided which flies opposite the disk 1, and reads data signals and sector servo signals from predetermined tracks. Since this sector servo signal is discretely written on the disk 1 every several hundred μs, the signal read by the magnetic head 4 is a discrete time signal that exists only at each sample time.

This signal is demodulated by a track number demodulation circuit 5, a position signal demodulation circuit 6, and an AD converter 7 to determine the position of the current sample time. In the switching control 8, seek control 9. is performed according to the deviation between the current position and the target 1-rack. Control operations are switched in the order of settling control 1o and following control 11.

First, seek control 9 moves the magnetic head near the target track by speed control. Next, the settling control 10 pulls into the target track by position control. Finally, the following control 11 performs positioning to follow the target track while reading and writing data. The manipulated variables calculated in these controls are switched by a changeover switch 12.

f) Output from the A converter 13. This output is amplified by the back amplifier 14, and the voice coil motor 15
to drive and control. This moves the carriage 16,
The magnetic head 4 is positioned on the target track.

FIG. 2 is a block diagram of the settling time in FIG. 1. Reference numeral 17 is a model representing the inertia of the positioning mechanism, and its output represents the current position of the magnetic head. In settling control, the positional deviation between the current position of the magnetic head and the one-track position is obtained like a subtracter 18, and position feedback control is performed so that this becomes zero.

A phase lead filter 19 is inserted in series in this loop, and the manipulated variable m is outputted to I! & Stabilizes the system by compensating for the phase delay of the structure. Furthermore, this phase lead filter 1
By selecting filter characteristics No. 9, it is possible to appropriately determine the coordination, damping characteristics, and steady-state characteristics of the settling control determined by this loop. Phase lead filter 19
In the present invention, it is assumed that the transfer function is expressed by the following equations (1), (2), and (3). G1 is a -order phase advance filter for low frequencies.

G2 is a high-frequency phase advance filter, and Gc is a combination of these in series.

Gc(S)=Kc-Gt-G2-(1)
T a S + 1 T4S+1 where Kc... Gain Tz... Time constant of this filter T3... Time constant of this filter Tz... Time constant of this filter T4... Time constant of this filter Figure 3 shows a phase advance filter 19 expressed by equation (1).
This is the frequency characteristic of Partially overlap between 1/T2 and 1/T8 so that the lower bending point 1/T2 of the high-pass filter G2 is on the low frequency side of the upper bending point 1/T3 of the low-pass filter G+. are connected in series, and the phase advance filter G
Configure c. Looking at the gain characteristics of this phase lead filter Gc, as a -order phase passing filter, the gap between the upper and lower bending points is wide, and unlike the -order phase passing filter, the gap between the upper and lower bending points is wide. There is a part with a large slope in between.

Therefore, looking at the 1st phase characteristics, as a -order phase passing filter, there is a wide region where the phase lead is large, and unlike a -order phase passing filter, the phase lead is sufficiently large between the upper and lower bending points. There are parts.

These characteristics have a high degree of freedom since the four constants T1 to T4 of the filter can be selected, and appropriate characteristics can be realized.

FIG. 4 is an open-loop frequency characteristic of the settling control loop shown in FIG. 2. The solid line is the frequency characteristic of the inertia 16.17 portion of the positioning mechanism in FIG. 2, and since the phase delay is 1180°, it is an unstable element. On the other hand, if the phase advance filter 19 with the characteristics shown in FIG. 3 is inserted in series to stabilize the system by compensating for the phase delay of the mechanism, an open loop frequency characteristic as shown by the broken line will be obtained. At this time, the gain Kc of the phase advance filter Gc is determined so that the maximum value of the phase advance is near the cutoff frequency fc where the gain of the open loop frequency characteristic is zero. Looking at the gain characteristics, there is a region of zero gain near the cutoff frequency fc, but it is not very wide, and a region with a gentle slope of the gain spreads on this low frequency side and high frequency side, and furthermore, on this low frequency side The gain on the high frequency side has a slope equal to the inertia of the positioning mechanism.

Therefore, looking at the phase characteristics, the cutoff frequency fc
The phase advance is large in a wide area centered on , and a sufficient phase margin is obtained. Also, the gain at the frequency f, where the phase is 1180' is:

It is sufficiently small, and sufficient gain margin is obtained.

Such good open-loop frequency characteristics suggest good closed-loop frequency characteristics, which in turn can improve the performance of closed-loop transient response.

That is, in settling control, the vehicle can quickly approach the target track, have little overshoot, and have good damping, so settling time can be shortened.

However, the transfer function expressed by equation 1) is a transfer function of a phase lead filter in the continuous time domain.

The sector servo method uses a discrete time domain phase lead filter, a so-called digital filter, which performs processing at a sampling period determined by the sector interval. For this reason,(
1) It is necessary to transform the equation from the continuous time domain to the discrete time domain, but this can be done mechanically, for example, by bilinear transformation expressed by equation (4).

As a result, the phase advance filter 19 expressed by equation (1) can be expressed as follows.

Here, al+82. a3, bz+ba are constants of this filter.

This can be easily converted into software using a microcomputer or the like.

〔Effect of the invention〕

According to the present invention, the degree of freedom of the phase advance filter for settling control is high.

Therefore, it is possible to appropriately set the cutoff frequency 1 phase margin, gain margin, etc. to improve the transient characteristics of settling control, so it is possible to shorten the settling time to easily pull in the target 1 to easily, and to prevent overflow from the target track. Shoots can be kept small.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a control device for a magnetic disk drive according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a settling control system of the control device of the present invention, and FIG. 4 through 4 show frequency responses for explaining the characteristics of the control device of the present invention.

Claims (1)

[Claims] 1. In a control device for a magnetic disk drive, which consists of seek control to move the magnetic head to a target track using a sector servo method, settling control to pull the magnetic head into the target track, and following control to follow the target track, the settling control The digital filter is a combination of first-order phase advance filters for low-pass and high-pass in series, and the lower bending point of the high-pass filter is on the low frequency side of the upper bending point of the low-pass filter. A control device for a magnetic disk device, characterized in that: