JPS639084A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To reduce the variance of transient response by switching a speed following control to a position following control after a fixed time has passed since a magnetic head passed through a prescribed position before a seek target track. CONSTITUTION:Every time a speed reference signal passes through the center of each track or the in between of adjacent tracks while the magnetic head is seeking, said signal is updated and applied to a servo circuit. A position A detector detects a position A a 1/2 track is almost continuously dropped to zero after a time counter built-in a CPU counts about 200musec. Since the operation is switched to the position following control the moment said signal comes to zero, the overshoot and variance of the transient response after control switching are small even if a following error is great in the speed following control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic head positioning servo for a magnetic disk device.

[Summary of the invention]

The present invention provides a magnetic head positioning servo for a magnetic disk device in which the magnetic head passes through a position A in front of the seek target track when switching from velocity follow-up control during magnetic head seek to position follow-up control in which the magnetic head is positioned on the target track. Then, by switching to position follow-up control after a certain time interval, variations in transient response after control switching are reduced.

[Conventional technology]

Conventional magnetic tisf devices, when a magnetic head leaks,
This is speed tracking control that drives the voice coil motor by converting the difference between the seek speed signal of the magnetic head and the speed reference signal into a current in the voice coil motor drive circuit.
Position tracking control is performed on the target track using methods such as PID control and precision compensation of position signals. 1/
The switch was made two tracks before (hereinafter referred to as position B).

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, the tracking error in speed tracking control usually varies by several cTrL/sec due to gain variations in the speed signal reproducing circuit, variations in the external force applied to the magnetic head, variations in the force constant of the voice coil motor, etc. must be expected. Considering the transient response after control switching, the speed of the magnetic head at the time of control switching should be as small as possible. However, if the design value of the magnetic head speed at the time of control switching is designed to be small at and b, due to the above-mentioned variations, There are problems in that the speed is too slow and it takes a long time to reach the switching position B, and when the design value is increased, overshoot in the transient response increases and settling time becomes longer. The present invention is intended to solve these problems, and its purpose is to improve the transient response after control switching by taking into account variations in follow-up error in speed follow-up control.

[Means to solve the problem]

The magnetic disk device of the present invention includes at least one servo head, at least one magnetic disk having a servo surface, and at least one voice coil motor for driving the magnetic head. When switching from velocity follow-up control during magnetic head seek to position follow-up control in which the magnetic head is positioned on a target track, a function is provided to detect that the magnetic head has passed a certain position A in front of the seek target track. The magnetic head has a function of detecting a fixed time interval after the magnetic head passes the position A, and is characterized in that the control is switched to the position following control after the fixed time interval.

[Effect]

According to the above configuration of the present invention, since the control is switched after a certain time interval after the magnetic head passes the position A before the center of the target track, the speed is changed due to variations in the tracking error in the speed tracking control. If the variation is large,
Control is switched near the center of the target track, and if the speed fluctuates on the small side, control is switched at a location far away. Considering transient response, the closer the switching position is to the center of the target track, the better, and the lower the speed, the better. However, if the speed varies in the large direction, the switching position will be better than when switching at position B in the prior art. Since speed follow-up control is performed up to a point close to the center of the target track, the position and speed at the time of switching are smaller than in the prior art, and the transient response is improved. If the speed varies in the smaller direction, the position and speed at the time of switching will be larger than in the prior art, which will be worse, but this will not be a problem because the transient response will be better compared to a pigeon house in which the speed varies in the larger direction. Further, when the speed varies toward the smaller side, there was a problem in the prior art that it took a long time to reach the switching position B-1, but this invention eliminates this concern.

〔Example〕

FIG. 1 is a block diagram in an embodiment of the present invention,
In speed follow-up control, switch 4.5 is on and switches 1 and 2.3 are off.

The gain of the speed signal is Qv, and the difference between the speed signal and the speed reference signal is converted into a current in the voice coil motor drive circuit (gain) (a), and the voice coil motor (force running number K r /M) is Drive. The multiplication table position information written on the servo surface is reproduced (gain Kpd), and a speed signal is obtained by differentiating the position signal.

Switching from speed follow-up control to position follow-up control involves detecting the position A from the position signal with a position A detector, detecting a fixed time interval with a built-in counter (shown as a time counter) of the CPU, and then Switches 1 to 51r in the figure: 1st
I always turn it on and off according to the table.

Table 1 The position tracking control uses PrD control, and the gains of the proportional (P signal), integral (engine signal), and differential (D signal) signals of the position signal are expressed as Gp1Gx%GD, and the gains of the three signals are expressed as follows: The sum is input to the voice coil motor drive circuit. The speed reference signal is updated and added to the servo circuit each time the magnetic head passes through the center of each track and between adjacent tracks during leakage, and from 1/2 track before the center of the target track, the speed reference signal Using a counter, the value is reduced from a certain value to zero almost continuously over a period of approximately 200 μsec (see Figure 2).
. The control is switched at the point where the aforementioned speed reference becomes zero, so in the end, the control is switched 1 from the center of the target track.
After the magnetic head passes the position before the /2 track (corresponding to the position AK), the control is switched approximately 200 μsea after the magnetic head passes the position before the /2 track (corresponding to the above-mentioned position AK), as counted by the built-in counter of the CPU.

FIG. 2 shows the magnetic head speed signal and the speed reference signal as a function of time, and shows two tracks before and after the target track. Normally, the speed reference signal is not added to the servo circuit in a stepped manner as shown in Figure 2, but is smoothed by passing it through a low-pass filter or interpolating with a position signal, but for simplicity, it is shown in Figure 2. I did it like this. Although the speed signal does not necessarily decelerate in a straight line, it is shown in Fig. 2 for simplicity. The solid line in Figure 2 shows the speed signal and speed reference signal under standard conditions (design conditions) IC, and the position and speed at the time of control switching are -
Xfi, υ. The dotted line shows the case where the tracking error is the largest, and it can be seen that since the speed is fast, the time to cross between tracks is short and the speed reference signal is updated quickly. Position and speed when switching control is 5-X1ls
υh, and of course 'Xh1<1x31, there is a sekiho of υ6 x υh. The one-point parallel line is the case where the tracking error is the smallest, and the position and speed at the time of control switching are -XL,
It is υL. The above three conditions (-X8+υS), (-X
FIG. 3 shows a transient response when control is repeatedly switched at htυh), (-XL, υL), and the time axis starts at the time of control switching. The vertical axis represents the position signal, where zero is the center of the target track, and it can be seen that the signal is settling while overshooting. As can be seen from Figure 3, the worst condition for the transient response is (
Xh+υh), and the problem arises when the following error in speed control is maximum. FIGS. 4 and 5 illustrate the case of the conventional example, in which control switching is performed when the target track passes a position (-Xs) slightly before the center of the target track. In this case, under standard conditions (−X8pυS
), and in the minimum case, it is switched at (-X3.υLL). As can be seen by comparing Figures 2 and 4, when the tracking error is maximum, it takes less than 200 μsec to move from 1/2 track before to -X8, so the switching speed υhh is I like dogs more than υh. That is, the transient response is improved under the condition υh υhh p Xh<Xs, as can be seen by comparing FIGS. 3 and 5 (dotted lines in each figure).

When the tracking error is the minimum, the transient response is worse compared to the conventional example, but it is still good compared to the standard condition, so there is no problem. In addition, in the conventional example, if υLL becomes too small, it takes a long time to reach the control switching position (Xs), and it becomes susceptible to disturbances, etc., but in this example, the control passes just before 1/2 track. After that, the control is switched at a certain time (approximately 200μ5ec), so υL
No problem occurs even if it becomes small.

〔Effect of the invention〕

As described above, according to the present invention, when switching from speed tracking control to position tracking control, the control is switched after a fixed time interval after the magnetic head passes position A in front of the seek target track. Even if the tracking error in speed tracking control is large, the overshoot in the transient response after control switching does not become very large, and even if the tracking error is small and the seek speed of the magnetic head decreases, the seek time does not become too long. have an effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the magnetic disk device of the present invention. FIG. 2 is a diagram showing a speed signal and a speed reference signal in speed follow-up control of an embodiment of the magnetic disk device of the present invention. FIG. 5 is a diagram showing a transient response after control switching of an embodiment of the magnetic disk device of the present invention. FIG. 4 is a diagram showing a speed signal and a speed reference signal in conventional speed follow-up control. FIG. 5 is a diagram showing a transient response after control switching in a conventional example. Applicant Seiko Epson Co., Ltd. Serious (forceful customer φ1 Figure 1 Figure 2 Paddle fA4 Figure 3

Claims (1)

[Claims] (1) When a magnetic head leaks in a magnetic head positioning servo of a magnetic disk device having at least one servo head, at least one magnetic disk having a servo surface, and at least one voice coil motor for driving the magnetic head. When switching from speed tracking control to position tracking control in which the magnetic head is positioned on the target track, it is detected that the magnetic head has passed a certain position (hereinafter referred to as position A) in front of the seek target track. a magnetic disk device having a function of detecting a fixed time interval after the magnetic head passes the position A, and switching to the position tracking control after the fixed time interval. .