JPS6255227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo signal written on a servo surface of a disk for head positioning in a magnetic disk device, and more specifically, to a servo signal written on a servo surface of a disk for head positioning in a magnetic disk device. The present invention relates to a method for correcting the difference in position sensitivity between the outer circumferential side and the inner circumferential side when writing servo signals.

In recent magnetic disk drives, a servo signal is written on one side of the disk to position the head positioner, and the head is positioned based on this signal.The patterns used as this servo signal are so-called tri-bit patterns and di-bit patterns. Patterns or patterns based on them are the mainstream. Each pattern has its own characteristics, but the di-bit pattern has more complicated circuits for servo bit detection and sync bit detection than the tri-bit pattern. It is possible to make the position sensitivity constant between the two positions. On the other hand, with tri-bit patterns, correcting the magnetization reversal distance tends to destroy the symmetry of the waveform, which is undesirable due to the nature of the pattern, so it is currently difficult to correct variations in position sensitivity between the inner and outer circumferences of the disk. It is.

A tri-bit pattern basically consists of an even pattern and an odd pattern, which are written alternately in the radial direction. FIG. 1 shows the state of magnetization reversal in these patterns and the waveform when it is read out by a head. As the head moves over these patterns written at alternating radial pitches, even and odd bit outputs are obtained depending on the position of the head. The position signal is obtained by detecting the peak values of even bits and odd bits and taking the difference between them, and is a triangular waveform signal having one cycle every two tracks. In the control circuit of an actual magnetic disk device, in order to correct the output difference between the outer and inner sides of the disk, for example, the circuit gain is controlled in proportion to the size of the sync bit of the servo pattern, or The circuit gain is controlled in proportion to the sum of even bits and odd bits. The magnitude of the position signal obtained in this way is fairly uniform from the outer circumference to the inner circumference of the disk. However, as the track pitch becomes narrower, this method alone cannot achieve uniformity, and the difference in output between the outer and inner peripheries of the disk becomes quite large.

On the other hand, in recent disk drives, closed-loop control is performed in which moving speed and position information are fed back to move and position the head. Many devices do not have mechanical speed detectors. Therefore, the speed signal must be electrically extracted from the position information, that is, the position signal. In other words, the speed signal is obtained by extracting the portion of the position signal that is proportional to the position and differentiating it with respect to time. Figure 2 shows this situation. Therefore, in order to obtain an accurate speed signal, the portion of the position signal that is proportional to the position must be constant over the inner and outer circumferences of the disk. In other words, when the head passes a track at a constant speed, the level of the position proportional portion of the position signal relative to the positional displacement (this is called position sensitivity) must be constant over the inner and outer circumferences of the disk. If this position sensitivity differs between the inner and outer circumferences of the disk, the actual speed and the electrically obtained speed when controlling the actuator will differ between the outer and inner circumferences, for example, from the outer circumference to the inner circumference. If the access time is different from the access time from the inner circumference to the outer circumference, or because the speed at which the head rushes in at the time of final head positioning is different, a problem occurs in which positioning cannot be performed.

To solve this problem, various improvements have been made to the control circuit. For example, it has been considered to correct the difference in position sensitivity by obtaining information about the head position on the disk surface and the position to be moved, but this would complicate the control circuit of the device and be disadvantageous in terms of cost. be.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a servo signal writing method that can obtain constant position sensitivity over the inner and outer circumferences of a disk without causing the problems described above. A feature of the servo signal writing method of the present invention is that the track pitch of the servo signal is made larger toward the outer circumference of the disk.

Hereinafter, the present invention will be explained in detail in the case of a servo signal with a tri-bit pattern, but it goes without saying that the present invention can also be applied to servo signals with other patterns.

Now, if we consider the difference in position sensitivity depending on the position on the disk surface, it is the magnitude of the data signal on the track where the servo head is located when reading the signal written on the disk surface, and the magnitude of the data signal from the adjacent track. This is due to the fact that the ratio of the magnitude of the wafting signal is different between the inner and outer circumferential sides of the disk. In other words, when a servo signal is written for one track on the disk surface using a servo head with an appropriate core width at a certain track pitch, and this track is read by moving the head in the track direction, the magnitude of the signal obtained is the third. As shown in the figure, even if the head completely moves to the next track position, the signal level does not become zero. Here, V _A is the signal level read when the head is directly above the track, and V is the signal level read when the head is completely above the adjacent track.
If _B , then the variation in position sensitivity means that the ratio of V _A to V _B is different at the inner and outer circumferences of the disk. The reason for this is that the leakage magnetic flux density in the circumferential direction and the radial direction at the magnetization reversal point changes depending on the track position because the magnetization reversal distance changes between the inner and outer peripheries of the disk.

Based on the above considerations, the servo signal writing method of the present invention makes the ratio of V _A to V _B constant over the inner and outer circumferences of the disk by changing the track pitch of the servo signal depending on the radial position of the disk. The basic idea is to try. below,
The relationship between track pitch and the ratio of V _A to V _B will be explained with reference to FIGS. 4 and 5.

By using a head with a certain appropriate core width W, track pitches T are formed on the disk surface in the order of odd pattern, even pattern, and odd pattern.
When data is written and the signal is read out, the change in the readout signal is as shown in FIG. In the same figure, the even signal output when the head is directly above the even pattern is V _E , and the side-to-side signal outputs from the adjacent odd tracks are V _OL and V , respectively.
If _OR , then track pitch T and V _E , V _OL , V _O
A relationship as shown in FIG. 5 is found between _R. As is clear from FIG. 5, when V _E becomes smaller than a certain track pitch, it suddenly begins to be influenced by adjacent tracks and decreases. Similarly, V _OL is affected and decreases when adjacent even patterns are written, but V _OR is hardly affected by writing of other patterns. The actual servo pattern is a repetition of signals written in this way, so if the head is directly above a certain even track, the even signal output is _VE , and the side output from the adjacent odd track is ( _VOL +
V _OR ). The ratio of V _E to (V _OL +V _OR ), which is involved in position sensitivity, changes greatly by changing the track pitch when writing a servo pattern.

On the other hand, as mentioned above, what is extracted as a position signal is V _E - (V _OL + V _OR ), and the position sensitivity S _P is within a certain range of track width T: S _P = V _E - (V _OL + V _OR )/T It was found from the experimental results that it can be expressed as Therefore, when changing the track pitch on the inner and outer circumferences, including the conventional gain control, we can express it in the formula:
The position sensitivity S _P at the inner and outer circumferences is as follows.

S _{P OUT} = {V _E − (V _OL + V _OR )} OUT/T (OU
T) x 1 (outer circumference side) S _{P io} = {V _E − (V _OL + V _OR )}in/T (in)
×G _C (Inner circumference side) However, G _C = {V _E + (V _OL + V _OR )}in/{V
_E (V _OL + V _OR )} OUT OUT means the outer track, and in means the inner track.

In the conventional servo signal recording method, T _(io) = T _(OUT
) , the position sensitivity is S _P OUT < S _P in , that is, {V _E − (V _OL + V _OR )} _OUT < {V _E − (V _OL + V _OR )} in × G _C It has been confirmed that there is a difference in position sensitivity of approximately 15% between the outermost circumference and the innermost circumference.

According to the present invention, by increasing the track pitch on the outer circumferential side of the disk and decreasing the track pitch on the inner circumferential side, {V _E (V _OL +V _OR )} _OUT > {V _E -(V _OL +V _OR )}in×G _C can be done. As the denominator of the equation for position sensitivity S _P changes, the numerator also changes in the same direction, but since the rate of change of the numerator is greater, it is possible to satisfy S _{P OUT} > S _{P io} .

According to experiments, the track pitch on the outer circumference side of the disk T _OUT = 1.5W, and the track pitch on the inner circumference side Tin =
By setting it as 1.35W (where W represents the core width of the head) and changing the middle in 4 stages,
The 15% difference in position sensitivity between the inner and outer peripheries, which could not be corrected in the past, could be completely corrected, and the actuator could be controlled well without the need for a special correction circuit. The range of the track pitch is indicated by diagonal lines in FIG. Furthermore, even if the track pitch of the servo signal is changed in this way, the data track pitch becomes the same track pitch as the servo track pitch, so there is no adverse effect on the write/read characteristics to the data track (i.e., the servo track pitch does not change). (The data track is written at the same track pitch.)

As is clear from the above explanation, although the servo signal writing method of the present invention is characterized by increasing the track pitch of the servo signal toward the outer circumference of the disk, This does not mean that the track pitch must be changed continuously, but also includes changing the track pitch stepwise as in the above experimental example.

The present invention, as described above, has the effect of easily making the position sensitivity constant over the inner and outer circumferences of the disk.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a tri-bit pattern servo signal and its readout signal waveform, Fig. 2 is a diagram showing a position signal obtained from a tri-bit pattern servo signal and a speed signal electrically generated from it, and Fig. 3 is a diagram showing a position signal obtained from a tri-bit pattern servo signal and a speed signal electrically generated from it. The figure illustrates the leakage of signals due to magnetic flux leakage from a single track, Figure 4 illustrates the readout signal when multiple servo signal tracks are adjacent, and Figure 5 illustrates the relationship between the track pitch and the readout signal. It is a relationship diagram.

Claims (1)

[Claims] 1. A servo signal writing method characterized in that, when writing a servo signal as a head positioning scale onto a magnetic disk, the track pitch of the servo signal is made larger toward the outer circumference of the magnetic disk.