JPH0311027B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a head positioning system, and more particularly to a method for forming a track positioning signal for a movable head of a magnetic disk drive having a movable head and a control system therefor.

(b) Prior Art and Problems Conventionally, in small flexible disk devices having a movable head, rough positioning of the head has been performed by open loop control using a step motor. These are 100 to 200 TPI (tracks per inch)
It has achieved a track density of This is 250 to 120 μm in track pitch. When attempting to further increase the track density, the media is affected by deformation due to temperature and humidity, making it impossible to accurately position the head relative to the track. For example, room temperature 0
The medium deforms by about ±20 μm when the humidity changes at ~30°C and humidity from 30% to 80%.

Furthermore, in small flexible disk devices, the recording capacity has been significantly increased through development and improvement of recording media and recording methods such as perpendicular recording. Under these trends, it is strongly desired to further improve head positioning accuracy.

(c) Object of the Invention An object of the present invention is to provide a head positioning method that enables more accurate positioning in a small disk device having a movable head.

(d) Structure of the Invention A feature of the present invention is that in the servo signal area of tracks provided concentrically on a magnetic disk, the positions in the width direction of the tracks are set to 1/N of the track width across a plurality of adjacent tracks. (N is a positive integer) to form a written servo signal, sample the servo signal multiple times in the circumferential direction with a magnetic head, detect the servo signal, and detect the servo signal in one period of the servo signal. Each signal belonging to the magnetic head is binarized at a predetermined slice level, the bit distribution of the pulse train corresponding to the binarized signal is determined, the bit distribution is compared with a standard distribution, and the track of the magnetic head is determined based on the distribution deviation. The purpose is to know the amount of positional deviation relative to the position.

(e) Embodiment of the Invention An embodiment of the present invention will be described below with reference to the drawings.

Figures 1 to 3 are diagrams for explaining the principle of one embodiment, and Figures 1 and 2 show the configuration of servo signals and position error pulse trains formed on even and odd tracks. FIG. 3 is a distribution diagram showing the probability of appearance of pulses for each bit number in the position error pulse train. In addition, Figure 1a
In FIG. 2A, the vertical direction in the figure is the radial direction of the magnetic disk, for example, the top is the outer circumferential direction, the bottom is the central direction, and the horizontal direction is the circumferential direction.

In Figures 1 to 3, 1 is a servo head;
2 and 3 are even and odd numbered tracks, 4
is a servo signal.

In this embodiment, the servo signals are shown in Fig. 1a and Fig. 2a.
As shown in FIG. 2, the servo signals to be written in the servo signal area A are shifted in the radial direction by 1/N of the track width (N=4 in this embodiment).

An example in which the servo signals thus formed are detected by heads located on even-numbered and odd-numbered tracks will be explained with reference to FIGS. 1 and 2, respectively.

As shown in FIG. 1, when the head 1 passes over an even numbered track 2, a detection signal as shown in FIG. 1B is obtained as the head output at each magnetization reversal position. As shown in the figure, the magnitude of the head output signal is maximum where the radial position of the servo signal 4 coincides with the trajectory of the head 1.
When the center line of head 1 coincides with the center line of even-numbered track 2, the servo signal 4 becomes maximum where it coincides with the even-numbered track 2, and decreases as it deviates from track 2. .

This head output signal is selected by a gate signal as shown in FIG. If this operation is repeatedly performed with the slice level set to about 50% of the maximum amplitude, the radial resolution becomes 1/N, or in this example, 1/4. Therefore, the first two cycles of one cycle shown in the diagram
The first and last two pulses will be “0”, and the three in the center will be “1”, but the third pulse from the beginning and the third pulse from the end will be “0” or “1” with a probability of approximately 1/2. 1”. Therefore, the binary signals “000111000”, “001111100”, “000111100”,
There is a possibility that four types of pulse trains of "001111000" are output.

Next, as shown in FIG. 2a, when the center of the head 1 passes over the center line of an odd-numbered track 3, a head output as shown in FIG. 2b is obtained.
When this is binarized using a slice level of approximately 50% of the maximum amplitude as described above, the first and last two pulses are "1" and the three in the center are "0".
Therefore, the first and third pulses from the end each become "0" or "1" with a probability of approximately 1/2.
Therefore, in this case, the binary signals are "111000111", "110000011", "111000011", etc.
11000111" four types of pulse trains may be output.

When the operations in Figures 1 and 2 above are repeated multiple times, each bit of the resulting pulse train is set to "1".
The probabilities of occurrence of are shown in FIGS. 3a and 3b, respectively.

Figure 3a shows the probability distribution when the radial position of head 1 exactly matches an even numbered track, the horizontal axis shows the bit number, and the vertical axis shows the probability that "1" appears. . As seen in the figure, in this case, a convex distribution is formed with the fifth bit as the median value and tails symmetrically on both sides.

When the radial position of head 1 exactly coincides with the odd-numbered track, contrary to the previous case, as shown in Fig. It exhibits a concave distribution.

Now, suppose that the radial position of head 1 is slightly offset from the center of the track. For example, if head 1 is shifted slightly downward from the position shown in FIG. Move to the 6th bit. If the position of the head 1 is shifted toward the outer circumference, the center of distribution moves in the opposite direction.

Therefore, by using the distributions shown in Figure 3 a and b as the standard and knowing the amount and direction of movement of the center position of the distribution of the actually detected binarized output with respect to the standard, it is possible to accurately determine the position of head 1. I can do it. In other words, the binary output can be used as a position error pulse for detecting the position of the head 1.

In this embodiment, the head 1 is positioned using this principle.

FIG. 4 is a block diagram showing the configuration of a demodulation circuit which is a main part of the above embodiment. In the same figure, 1
1 is a servo head, 12 is a preamplifier, B is a demodulator, which includes an AGC (automatic gain adjuster) 13, an amplifier 14,
It consists of a logic circuit 15, a position error detector 16, and a level sensor 17, and 18 is a shift register.

The output signal of the head 11 is amplified by a preamplifier 12 and sent to an amplifier 14 and a logic circuit 15 via an AGC 13. The logic circuit 15 generates a gate signal for demodulation (see FIG. 1c and FIG. 2c),
This signal is sent to a position error detector 16. On the other hand, the head output amplified by the amplifier 14 is serially input to the position error detector 16, and a specific signal is selected and pulsed by the gate signal. The result is then latched by shift register 18. Note that the preamplifier 13 performs gain control based on the output of the level sensor 17.

FIG. 5 is a circuit diagram showing the main part of the position error detector 16, in which head outputs are sequentially selected and sent to the comparator 19 by gate signals. 20 is a slice level setting circuit, which allows the slice level to be set to a desired value. The comparator 19 sequentially binarizes the input head output by comparing it with this slice level, and sends it to the shift register 18 as a pulse train of "1" and "0". Note that +E ₁ and −E ₁
is the operating power supply.

FIG. 6 shows that using the position error signal which is the parallel output from the shift register 18 of this embodiment,
FIG. 2 is a block diagram of main parts showing the configuration of a positioning circuit for positioning the head.

In the figure, 22 is a demodulator (the part indicated by the dashed line B in FIG. 4), 23 to 25 are I/O ports, 26 is a digital-to-analog converter (DAC), 27 is a power amplifier, and 28 is a Step motor, 29 is clock generator (CLK), 30
3 is a central processing unit (CPU), 31 is a main memory consisting of RAM, and 32 is a ROM in which a program for executing the present embodiment is written.

The position error signal stored and latched in the shift register 18 as described above is stored in the RAM 31 via the I/O port 23, and this storage operation is repeatedly performed multiple times. and
The CPU 30 calculates these averages and determines the position of the head 11 with respect to the track as described above. Next, a signal indicating the amount and direction of positional deviation of the head 11 detected by comparison with the standard distribution is outputted to the DAC 26 via the I/O port 24 as a control signal. This signal is DAC2
After analog conversion by 6, power amplifier 2
For example, a four-phase step motor 28
The coil is applied to drive the motor 28 and adjust the position of the head 11.

The program for executing the above operations is stored in the ROM 32 in advance as described above. Note that the I/O port 25 is for interfacing with other external devices.

As described above, in this embodiment, the position of the head can be accurately detected and the position of the head can be controlled with high precision.

In the above embodiment, a step motor 28 is used, but instead of this, a linear motor using a voice coil may be used.

(f) Effects of the Invention As explained above, according to the present invention, highly accurate head positioning in a small disk device having a movable head can be realized.

[Brief explanation of drawings]

FIGS. 1 to 3 are diagrams for explaining the principle of the present invention, and FIGS. 1a and 2a are diagrams showing servo signal patterns, FIGS. 1b, c, and 2b, 3c is a waveform diagram, FIGS. 3a to 3c are distribution diagrams, FIGS. 4 and 5 are diagrams showing an embodiment of the present invention, and FIG. 4 is a block diagram showing a demodulator of the above embodiment, FIG. 5 is a circuit diagram showing the main parts of the demodulator, and FIG. 6 is a block diagram showing the main parts of the positioning circuit according to the embodiment. In the figure, 1 and 11 are servo heads, 2
and 3 are even-numbered and odd-numbered tracks, 4 is a servo signal, 12 is a preamplifier, B and 22 are demodulators, AGC (automatic gain adjuster) 13, amplifier 1
4, consisting of a logic circuit 15, a position error detector 16, and a level sensor 17; 18, a shift register;
9 is a comparator, 20 is a slice level setting circuit, 23 to 25 are I/O ports, 26 is a digital-to-analog converter (DAC), 27 is a power amplifier, 28 is a step motor, 29 is a clock generator (CLK), 30 is the central processing unit (CPU), 31
32 is a main memory consisting of RAM, and 32 is a ROM in which a program for executing the present embodiment is written.

Claims (1)

[Claims] 1. In the servo signal area of tracks provided concentrically on a magnetic disk, the positions in the width direction of the tracks are shifted by 1/N of the track width (where N is a positive integer) across multiple adjacent tracks. A written servo signal is formed, the servo signal is sampled multiple times in the circumferential direction by a magnetic head, the servo signal is detected, and each signal belonging to one cycle of the servo signal is divided into two values according to a predetermined slice level. A head positioning system characterized in that the bit distribution of a pulse train corresponding to the binary signal is determined, and the amount of positional deviation of the magnetic head with respect to the track is determined from the deviation of the distribution.