JPH0792986B2 - Tracking control device for magnetic head - Google Patents

Description

The present invention relates to a track following control device for a magnetic head in a magnetic disk device using a sector servo system.

[Prior Art] In a magnetic disk device, a magnetic head control method called a sector servo method has been put into practical use. The sector servo system divides the data track on the surface of the magnetic disk into a plurality of sectors, arranges information (servo information) for controlling the magnetic head in each sector, and reads the servo information. This is a method for controlling the magnetic head. Figure 4 shows, for example, IEEE TRANSACTION ON MA
GNETICS, VoL.MAG-17, NO.4, JULY 1981, p.1396-1402, `` HIGH TRACK DENSITY FOR MAGNETIC DISK
DRIVES WITH AN “EMBEDDED SERVO” POSITIONING SYSTE
FIG. 5 is an explanatory diagram showing servo information in the conventional sector servo system disclosed in “M”, and FIG. 5 is a block diagram showing a conventional track following control device for a magnetic head described in the same paper.

In FIG. 4, (1) is a data track area on the magnetic disk surface, which is divided into n sectors of S ₀ , S ₁ , ... S _{n-1 in} a fan shape. S _i indicates that the sector has sector number i. (2) is an area in which data to be stored in each sector is stored (hereinafter referred to as a data area), (3) is an area in which information for magnetic head positioning control is recorded (hereinafter referred to as a servo area), The arrow R indicates the rotation direction of the magnetic disk. (4) is a write / read gap (hereinafter referred to as a head gap) of a magnetic head that is movable in the radial direction of the magnetic disk, and the portion immediately below it is sequentially read.
Each sector indicated by S _i passes, and at that moment, writing or reading of each information is performed. (5) is the data track, (6) is its center line, data track (5)
Are formed in concentric circles with a substantially uniform width, and the center point of the head gap (4) may follow the center line (6) of the data track (5) with a small error when writing and reading data. desirable. The servo area (3) is a servo area detection marker (ZB), synchronization and gain adjustment unit (ZP).
A), a track address section (ZAD) and a position error detection section (ZPOS). At the time of track following control, the magnetic head and the track Position error X _E is detected. In FIG. 5, X _T is the track displacement, X _H is the displacement of the magnetic head in the radial direction of the magnetic disk, and (7) is the position error X _E.
Is a signal processing circuit for converting to an electric signal e _p , (8) is a compensation circuit for performing phase compensation on the position error signal e _p for stabilizing the system and converting it to a drive signal e _D , and (9) is a magnetic head The drive mechanism for positioning moves the magnetic head toward the inner circumference side or the outer circumference side in the radial direction of the magnetic disk according to the drive signal e _D.

Since the servo area (3) is provided for each sector, the track length direction (magnetic disk circumferential direction)
Are formed discontinuously. Therefore, the position error signal e _p is (i + 1) after detecting the i-th sector information.
This must be held until the second sector information is input, and the position error detector (10) including the signal processing circuit (7) shown in FIG. 5 includes a sample hold function. Yes, the control system of FIG. 5 is a sampled value control system. In the sample value control, it is said that it is desirable to set the sampling frequency f _S to about 10 times or more with respect to a predetermined servo band f _C. Therefore, if an attempt is made to expand the servo band in order to improve track following performance, the sampling frequency must be increased, but this cannot be increased so much due to the limitation on the data recording photomat.

In order to expand the servo band without increasing the sampling frequency, a track follow-up control device that uses auxiliary control information in addition to the servo information for each sector described above is disclosed in, for example, JP-A-59-175070. It is disclosed in JP-A-52-15309.

The former uses an optical encoder as an auxiliary means for obtaining the position information of the magnetic head, and the latter uses one of a plurality of magnetic disk surfaces as a dedicated servo information surface. FIG. 6 is a block diagram showing these conventional track following control devices. In the figure, (11) is a magnetic head position sensor, which is combined with an optical encoder or servo information dedicated surface (not shown) to form a magnetic head. The displacement X _H is electrically detected as a displacement signal e _H. The displacement signal e _H is a continuous signal unlike the position error signal e _p . Therefore, by using the high frequency component of this displacement signal e _H , it is possible to broaden the band of the track following control loop, and the position error signal e _p after passing through the low pass filter (13) and the displacement signal The signal after passing e _H through the high-pass filter (12) is combined at the addition point (14) and sent to the compensation circuit (8).

In the track following control device shown in FIG. 6, the magnetic head displacement
X _H to magnetic head position sensor (11), high-pass filter (1
Although the path passing through 2) is configured as a minor loop, it is necessary to consider the external input to the track following control system due to the recent trend toward miniaturization and weight reduction of magnetic disk devices. That is, there occurs a situation in which the optical encoder itself, which should be used as a reference reference for the magnetic head position, is displaced by external vibration or the like and affects the track following performance. FIG. 7 shows such an optical encoder displacement
A block diagram showing a conventional track following control device considering X _{O. In} the figure, there are two systems of input, track displacement X _T and optical encoder displacement X _O. It is necessary to secure it. 8 and 9 show the loop transfer characteristics between the track following control systems. Track displacement when the optical encoder displacement X _O is relatively large (for example, when vibration is applied to the device)
Since X _T can be seen to be approximately equal to the optical encoder displacement X _O , the path including the position error detector (10) and low pass filter (13) and the magnetic head position sensor (11) and high pass filter (12) FIG. 8 shows the open-loop transfer characteristic at that time, which is synthesized with the path including. On the other hand, when the optical encoder displacement X _O is small, it can be ignored and considered, resulting in a track following control system including a minor loop as shown in FIG. 6 and an open loop transfer characteristic shown in FIG. To get In terms of the design of the control device, it is desirable that the two characteristics match, but as a result of adjusting each part to satisfy the required performance, the two characteristics may not match. In this case, the design is advanced with one of them as the main and the other as the sub, and the characteristics of the compensation circuit (8) are set according to the main one. The open-loop transfer characteristics shown in FIGS. 8 and 9 are set to match the characteristics of FIG. 8, that is, the track following control characteristics when the optical encoder displacement X _O is large.

[Problems to be Solved by the Invention] Since the conventional track-following control device for a magnetic head is configured as described above, there are two _types in consideration of the displacement X _O of the magnetic head displacement detection means itself such as an optical encoder. There is a problem that it is difficult to realize sufficient transfer characteristics at the same time in both track following control systems.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a track following control device for a magnetic head having a sufficient transfer characteristic for both of two assumed track following control systems. And

[Means for Solving the Problems] A track following control device for a magnetic head according to the present invention is
Position error signal e _p between track displacement X _T and magnetic head position X _H
The position error detecting means for detecting the position error signal and the adding means for combining the low frequency component of the position error signal e _{p and} the high frequency component of the magnetic head displacement signal e _H with each other. In addition to the compensating circuit, a second compensating circuit for compensating the phase of the position error signal is inserted.

[Operation] In the track following control device for the magnetic head according to the present invention, by providing the second compensation circuit as described above,
The two types of track following control systems as described above are set so as to independently provide phase lead compensation, and sufficient transfer characteristics are realized.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. First
The figure is a block diagram showing an embodiment of the present invention. In the figure, (7) is a signal processing circuit, (8) is a first compensating circuit corresponding to a compensating circuit of a conventional example, and (9) is a magnetic head. A drive mechanism, (10) a position error detector that constitutes a position error detecting means, (11) a magnetic head position sensor that constitutes a magnetic head displacement detecting means in combination with an optical encoder (not shown), and (12) The high-pass filter, (13) is a low-pass filter, and (14) is an addition point which constitutes an addition means. The above is the same as the conventional example shown in FIG. Reference numeral (15) is a second compensation circuit that is inserted between the position error detector (10) and the low-pass filter (13) and performs phase compensation of the position error signal e _p .

That is, in the present invention, two compensating circuits, that is, the first compensating circuit (8) and the second compensating circuit (15) are used, each of which is one after the addition point (14) and the position error X _E is generated. Between the partial position error detector (10) and the addition point (14)
The feature is that they are arranged.

2 and 3 are open loop transfer characteristic diagrams in the track following control device for the magnetic head according to this embodiment.
The figure shows the case where the optical encoder displacement X _O is relatively large,
FIG. 3 shows a case where the optical encoder displacement X _O is negligibly small. The two angular frequencies (ω
_O , ω _E ) and the first compensation circuit (8) and the second compensation circuit
Phase compensation is provided by each of the compensation circuits (15).

In the open-loop transfer characteristic shown in FIG. 2, the loop gain becomes 0 decibel at the angular frequency ω _O , so that the first compensation circuit (8 ) Provides the phase compensation. However, in the open-loop transfer characteristic shown in FIG. 3, since the gain characteristic is different, the loop gain becomes 0 dB when the angular frequency is ω _E. Therefore, a sufficient phase margin cannot be secured only by the compensation by the first compensating circuit (8), so that the second compensating circuit (15) provides the phase lead compensation to secure a sufficient phase margin.

In the above embodiments, the auxiliary magnetic head displacement detecting means is described as an optical encoder, but other auxiliary means, such as a dedicated servo surface or a magnetic scale, may be used.

According to the present invention as described above [Effect of the invention], using two compensating circuit with respect to the track following control apparatus 2 input system magnetic head, a generation point of one of the position error X _E position Since it is installed in the path between the error detecting means and the adding means for the magnetic head displacement signal and the other one is installed after the adding means, the transfer characteristics are adjusted to be sufficient for the two types of track following control systems. There is an effect that a possible track following control device of the magnetic head can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 and FIG. 3 are open loop transfer characteristic diagrams in one embodiment of the present invention, FIG. 4 is an explanatory diagram showing servo information in a conventional sector servo system, and FIGS. 5, 6, and 7 are conventional magnetic fields. FIG. 8 and FIG. 9 are block diagrams showing a head track following control device, and are open loop transfer characteristic diagrams in a conventional example. In the figure, (1) is a data track area, (2) is a data area, (3) is a servo area, (8) is a compensation circuit (first compensation circuit), (9) is a drive mechanism, and (10) is Position error detector (position error detecting means), (11) magnetic head position sensor (magnetic head displacement detecting means), (12) high-pass filter, (13) low-pass filter, (14) addition point ( Adder means) and (15) are second compensation circuits. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A position error detecting means for detecting an error between a magnetic head displacement and a track displacement based on servo information obtained from a servo area for each sector on a magnetic disk data surface.
Auxiliary magnetic head displacement detecting means for detecting displacement of the magnetic head, which is installed at an arbitrary place other than the magnetic disk data surface, and a low-pass filter for taking out a low frequency component of the position error signal from the position error detecting means. A wide-range filter for extracting a high frequency component of the magnetic head displacement signal from the magnetic head displacement detection means, an addition means for inputting signals from both filters and outputting a combined signal thereof, and a combined signal from the adding means for input In a track following control device for a magnetic head including a compensating circuit for compensating the phase of a servo system, and a magnetic head driving means for moving the magnetic head according to a signal from the compensating circuit, A second compensating circuit for compensating the phase of the position error signal is inserted in the path between the adding means. Click follow-up control apparatus.