JPH0963216A - Magnetic disk device capable of canceling variation of track pitch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the accuracy of a track pitch and to improve the reliability of the device by canceling the variation of a track pitch for four track periods due to mutual interference in magnetic recording caused by a difference of a servo pattern in disposition. SOLUTION: The servo pattern to be recorded on the surface of a magnetic disk medium is composed of repetition of four continuous servo frames which are different from each another in the circumferential direction. Each servo frame consisting of one set or a plural number of dipulses in a burst form in order in the circumferential direction as positioning information of four sets of A, B, C and D is disposed in the radial direction. Each servo frame is composed of these four bits of positioning information and a synchronization pulse as periodical information of the servo frame. Since the same combined servo pattern is brought forward in identical order in any track, the variation of the track pitch can be canceled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device capable of canceling track pitch fluctuations, and more particularly to the structure of a servo pattern defining a track center line.

[0002]

2. Description of the Related Art Normally, cylinders (tracks) for recording data of a magnetic disk device are arranged in concentric circles in the order of hundreds to thousands. The magnetic head that reads and writes data is 15% of the average track pitch from the center line of this track.
If it deviates by more than a certain amount, read errors will increase rapidly, so it is necessary to design the servo system so that the magnetic head positions on the track with high accuracy.

The position signal of the magnetic disk device is generated by reading the servo pattern of the servo surface on which the positioning information is recorded by the servo head and demodulating by the demodulator. If the track pitch indicated by the position signal and the adjacent track are not uniform and the pitch fluctuates widely, the allowable off-track amount between the tracks having a narrow pitch decreases, and a read error easily occurs.

The recording density of the magnetic disk device has been improved year by year, and the track pitch is required to have higher accuracy.

Conventionally, as a typical servo pattern of a magnetic disk device, there is a two-phase modified dipulse pattern. This two-phase modified dipulse pattern is composed of a magnetization reversal pair called a dipulse (or dibit) as a basic element. An example thereof is shown in FIG. In the figure, the vertical line represents the magnetization reversal, and two adjacent lines form a dipulse.

In one servo frame, there is a sync portion composed of two consecutive dipulses in common in each track in the direction traversing the tracks, and thereafter, the A phase, B phase, C phase, and D phase.
Position information of the phase is placed. Then, the first pulse of the Sync part is called an ID pulse and the second pulse is called a sync pulse, and if two consecutive pulses exist, it is recognized as a sync signal. Further, the ID pulse is deliberately removed and the index indicating the starting point of one round is encoded and embedded.

The signal obtained when the two-phase modified die pulse pattern, which has been most widely used in the past, is read by the magnetic head, changes in amplitude due to waveform interference between the die pulse patterns on the front, back, left, and right. The baseline of the signal is also no longer linear, causing some undulations.

The demodulator separately takes out the peak amplitudes on one side of the A, B, C, and D phases in the read signal, and takes the difference between the pairs whose radial positions do not overlap with each other (that is, C -A, D-B), two sets of position signals 90 degrees out of phase with each other are generated. These position signals cause different offsets due to the amplitude change due to the above waveform interference and the waviness of the baseline,
The position of the track center may deviate from the ideal position.

There are four types of servo patterns corresponding to the track center, and they are repeated in a 4-track cycle. That is, the tracks 0, 1, 2, shown in FIG.
Although track No. 3 is different from each other, track 0 and track 4 have the same pattern arrangement. And since the waveform interference differs depending on how the patterns are arranged, the deviation amount of the track center changes,
The track pitch has a width of 4 track periods. Further, FIG. 5B shows a waveform diagram of the gate signal.

[0010]

If there is a fluctuation in the track pitch of four track periods, a read error is likely to occur between tracks with a narrow track pitch, and the reliability of the magnetic disk drive is degraded.

It is an object of the present invention to provide a highly reliable magnetic disk device which completely eliminates the fluctuation of the track pitch of four track periods due to the mutual interference of magnetic recording caused by the difference in the arrangement of servo patterns. .

[0012]

DISCLOSURE OF THE INVENTION The present invention is directed to a magnetic disk medium having a servo pattern recorded therein, which is formed by repeating four different continuous servo frames in the circumferential direction, and one set for each of the four servo frames. Or, in the form of a burst composed of a plurality of dipulses, which are arranged in the order of appearance time (circumferential direction) in a radial direction as position information of the A, B, C, and D4 phases, and are arranged in the four servo frames. It is characterized in that a sync pulse, which is synchronization information, and the above-mentioned four position information are included, and that servo patterns of the same combination appear in the same order in all tracks.

The four servo frames are arranged such that the entire radial arrangement of the position information of the A, B, C and D4 phases is shifted by 1 to 3 times the track width. It is characterized by

[0014]

Next, the present invention will be described with reference to the drawings.

FIG. 1A is a diagram of a servo pattern showing an embodiment of the present invention. Referring to FIG. 1A, the broken line in the horizontal direction indicates the center line of the track. The width of the servo head is 2 track pitches.
It is a little less than twice. Then, they are referred to as frame 1, frame 2, frame 3, and frame 4 in order from the left. Further, looking at the radial arrangement of the A, B, C, and D phases (vertical direction in the figure), the frame 2 has the frame 1 of the track numbers 0, 1, 2, 3, 4 ,. The layout is shifted in the increasing direction (downward in the figure). Similarly, frame 3 is the shifted version of frame 2 and frame 4 is the shifted version of frame 3. Then, when the frame 4 is shifted by another track width in the same direction, the same arrangement as that of the frame 1 is restored.

With such an arrangement, in the frame 1, the same pattern as that of the four track center positions that appear periodically in the radial direction appears in four consecutive frames of one track. That is, the patterns of four frames are different on one track center line, and there are four patterns. Moreover, although the start pattern is shifted, it can be seen from this figure that the same four patterns appear in the same order and are repeated on every track.

Next, FIG. 2 shows a servo signal waveform (reading waveform) when the servo head passes over the frame 1 of the track 0. From FIG. 2, it can be seen that when the servo head is located on the true track center, the A phase tends to sink more than the D phase.

Next, FIG. 3 shows a demodulator circuit for demodulating the servo signal.

Referring to FIG. 3, the servo signal read by the servo head 1 is amplified by the preamplifier 2 and input to the AGC amplifier (AGC) 3. The output of the AGC amplifier 3 is a 4-channel peak detector (PKD) 4, 5,
6 and 7 and a sync detector (SYNC DET) 10. These peak detectors 4, 5, 6, 7
The PKD4 of the channel 1 which is used in correspondence with the radial offset amount of the position information of the four phases and which has taken out the peak of the A phase in the frame 1 is the C phase in the frame 2 and the PKD4 in the frame 3
Then, the logic circuit must be configured to process the D phase and the B phase in the frame 4, respectively.

This is because the position information having the same radial offset amount appears in this order by changing the phases in the frame. Even if it seems complicated, it is easy for a person skilled in the art to judge how to replace the detection phases required for the decoding logic, assuming that the servo pattern is configured as shown in FIG. is there.

FIG. 1B shows the gate signal. FIG.
Referring to (b), G1, G2, G3 and G4 are shown in FIG.
It corresponds to the signals of the same name as shown in FIG. The outputs PD1 to PD4 of the peak detectors 4, 5, 6, 7 are the conventional 2
As with the phase modified dipulse pattern,
Combine them two by two and take the difference. That is, PD2
The operations of -PD1 and PD4-PD3 are performed by the differential amplifiers 8 and 9. Since their outputs have undulations having four consecutive frames as a cycle, the undulations are respectively cut by low-pass filters (LPF) 13 and 14, and two sets of position signals N that are 90 degrees out of phase with each other are provided. ，
Generate Q. FIG. 4 shows the waveforms of the output signals of the low pass filters 13 and 14.

Here, the cycle of the servo frame is 2 μse.
c, which is 8 μsec in four frames, so the frequency of the swell is 125 kHz or more. Therefore, the undulation can be sufficiently removed by using a second-order or higher-order low-pass filter having a cutoff frequency of about 1/10 thereof.

The sum of the four outputs of the peak detectors 4, 5, 6, 7 is fed back and compared with the reference voltage Vref to perform the AGC (automatic gain adjustment) operation, which is the same as in the conventional case.

Next, the sync detector 10 detects the sync pulse and synchronizes the clock of the PLO 11 with the servo frame. The timing generator 12 generates the gate signals G1 to G4 of the peak detector from the clock of the PLO 11 synchronized with the servo frame. The timing of G1 to G4 is
It is shown in FIG. 1 (b) corresponding to FIG. 1 (a).

Correspondence between G1 to G4 and frames 1 to 4 is possible by detecting the index embedded in the SYNC section and synchronizing with the timing as a reference. This will be apparent to those skilled in the art.

When the demodulated position signal is passed through a low pass filter, the swell component is removed and the off-track component due to waveform interference is averaged. Then, when averaged, the DC offset remains not zero, but even if it remains, the same pattern appears regardless of which track is positioned, so the remaining DC offset is equal between adjacent tracks. The track pitch doesn't go wrong.

On the other hand, Japanese Patent Application Laid-Open No. 3-207010 discloses a system similar to the present invention, and its pattern is shown in FIG.

This method attempts to cancel the offset due to waveform interference within four consecutive frames to make the average zero. However, when a track generates a track center position signal from A-B and B-A, the adjacent track generates a track center position signal from C-D and D-C. Since the phase used for signal generation differs between adjacent tracks, it seems that the track pitch fluctuations are not canceled completely.

Unlike the above, the principle of the present invention is to make the influence of waveform interference uniform and not affect the track pitch by forming the servo pattern so that the offset is the same in every track. That is, since the patterns of the same combination appear in the same order in every track, it is possible to completely eliminate the track pitch fluctuation due to the waveform interference of magnetic recording.

In addition to the waveform interference of magnetic recording, the offset of the peak detectors of the four channels due to the mutual variation also causes the track pitch to become wider or narrower.
BCD phase write the same pattern, 2 at that place
The offset can be canceled by measuring the offset between the two position signals N and Q and calibrating the offset.

Further, in the same manner as the one disclosed in the above-mentioned Japanese Patent Laid-Open No. 3-207010, G1 is set so that the position signal used for positioning is always output from the same set of peak detectors.
The circuit variation may be removed by a method of replacing the contents of G4 to G4 according to the target track.

Further, in one embodiment according to the present invention, the position information A, B, C and D is composed of one set of dipulses, but the same effect can be obtained even if the burst pattern is composed of a plurality of sets. It goes without saying that there is.

[0033]

As described above, according to the present invention, the servo pattern is formed so that the same offset is obtained in every track, and the influence of waveform interference is made uniform. There is an effect that it is possible to provide a highly reliable magnetic disk device by eliminating variations in track pitch between adjacent tracks.

[Brief description of drawings]

FIG. 1A is a diagram showing a servo pattern showing an embodiment of the present invention, and FIG. 1B is a waveform diagram of a gate signal of a demodulator circuit.

FIG. 2 is a waveform diagram of read signals in track 0 and frame 1 of the present invention.

FIG. 3 is a block diagram showing a configuration of a demodulator circuit that realizes the present invention.

4 is a waveform diagram showing an output signal of the demodulator circuit of FIG.

FIG. 5 is a waveform diagram of a conventional two-phase modified die pulse pattern and a gate signal.

FIG. 6 is a diagram showing an example of another conventional servo pattern.

[Explanation of symbols]

 1 servo head 2 preamplifier 3 AGC amplifier (AGC) 4,5,6,7 peak detector (PKD) 8,9 differential amplifier 10 sync detector (SYNC DET) 11 phase-locked oscillator (PLO) 12 timing generator 13, 14 Low-pass filter (LPF)

Claims (2)

[Claims] 1. A magnetic disk medium having a servo pattern recorded therein, which is formed by repeating four mutually different continuous servo frames in a circumferential direction, and a burst shape consisting of one set or a plurality of the four servo frames. In the order of appearance time (circumferential direction), the dipulses are arranged offset from each other in the radial direction as position information of the A, B, C, and D4 phases, the sync pulse that is the synchronization information in the four servo frames, and the A magnetic disk device capable of canceling track pitch fluctuations, characterized in that servo patterns of the same combination appearing in the same order on all tracks, including four pieces of position information. 2. The four servo frames are arranged so that the entire radial arrangement of position information of the A, B, C, and D4 phases is shifted by 1 to 3 times the track width. 2. A magnetic disk drive capable of canceling track pitch fluctuations according to claim 1.