JPS6249665B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a head position signal on a servo disk surface of a magnetic disk drive with high track density and good linearity.

A dibit pulse having both positive and negative polarities as shown in FIG. 1 is used as a head position detection signal in a conventional magnetic disk device. This signal consists of two types of position detection pulses at different positions in the circumferential direction.
ODD pulse and EVEN pulse to servo track 1
This is a method in which the layers are formed alternately on top. in this case,
The position detection servo head 10 has a servo track width.
It has almost the same core width as TW. The head position signal is expressed as the difference in amplitude between the ODD pulse and the EVEN pulse, and the servo head is located on the ODD track.
When located on the boundary of the EVEN track, the ODD pulse and the EVEN pulse have the same amplitude, and the position signal shows zero voltage, and shows the maximum value at each off-track. Figure 2 shows the detected waveforms in the radial direction in this case. The position is identified by counting the number of on-cylinders.

In such a conventional system, firstly, the linearity of the position signal deteriorates in an off-track state due to the influence of crosstalk between tracks. Secondly, as the track density increases, a servo head with a narrower core width becomes necessary, but as a result, there are drawbacks such as a poor S/N ratio and a large dependence on the quality of the medium.

In order to eliminate this drawback, a position signal detection method using four types of position detection pulses having different phases as shown in FIG. 3 has been proposed.

In the same figure, between clock pulse groups C ₁ and C _2, track T ₁ contains an O1 pulse, an E2 pulse, and a track T 1.
O1 pulse and O2 pulse for T ₂ , track T ₃
The E1 pulse and the O2 pulse are sequentially formed every four tracks, with one being common and the other being shifted, such as the E1 pulse and E2 on track _T4 . The servo head 10' for detecting this signal has a core width approximately twice the servo track width Tw, and the position signal detected thereby is as shown in the radial direction detection signal in FIG. The 1-phase position signal shown by the solid line and the 2-phase position signal shown by the dotted line are the track width Tw.
The four-phase track is identified by the pulse amplitude and phase as shown by the waveform with zero point at the track boundary (on-cylinder). The 1-phase position signal is the position error signal PES detected by the amplitude difference between the O1 pulse and the E1 pulse.
1, the two-phase position signal is positioned by the position error signal PES2 detected by the amplitude difference between the O2 pulse and the E2 pulse. The phase of this position signal is shifted by one track width Tw in the radial direction, which makes the head width wider and alleviates the above-mentioned drawbacks, but this position signal detection method also has the following drawbacks. .

That is, as shown in FIG. 5A, since this method of creating the position detection signal is performed by writing in the track direction, if a phase shift as shown by the dotted line in A in the figure occurs, the signal amplitude will fluctuate. Furthermore, during writing, disturbances in the magnetic field occur in the transition area as shown in Figure B, causing fluctuations in the signal amplitude as shown in Figure B, B', which deteriorates the linearity of the position detection signal. Become.

SUMMARY OF THE INVENTION An object of the present invention is to provide a head position signal detection system that increases the width of the servo head and improves the linearity of the position detection signal.

In order to achieve the above object, the head position signal detection method of the present invention is a head position signal detection method in which a head position detection signal is written on a predetermined surface of a plurality of disks of a magnetic disk device as a servo disk, and the head position is detected based on the signal. In this case, the position detection signal is written to the servo track by repeating four detection pulses with different phases in the circumferential direction for each track every four tracks, and the position detection servo head is written at two of the servo track width. It is characterized by having a core width that is more than twice as wide.

The present invention will be described in detail below with reference to examples.

FIG. 6 is an explanatory diagram showing the configuration of an embodiment of the present invention.

In the figure, between the clock pulse groups C ₁ and C _2, position detection pulses having different phases are written in each track from T ₁ ' to T ₄ '. That is, the T ₁ ′ track uses only the O1 pulse, the T ₂ ′ track uses only the O2 pulse, the T ₃ ′ track uses only the E1 pulse,
The T ₄ ' track is formed only by E2 pulses.
Also, a servo head 20 for detecting this signal.
The core width is made wider than twice the servo track width Tw, for example, about three times the servo track width Tw.

7a to 7d show the phase relationship of amplitude changes due to O1, O2, E1, and E2 pulses when the servo head 20 is moved in the radial direction x in the track configuration of FIG. 6, and this is detected by the servo head 20. This becomes the head position signal.

Difference between the amplitude of the O1 pulse and the amplitude of the E1 pulse V _O1
-V _E1 becomes the first phase position error signal PES1,
The amplitude difference V _O2 -V _E2 between the O2 pulse and the E2 pulse becomes the second phase position error signal PES2.

FIG. 8 shows the one-phase position error signal PES1 and the two-phase position error signal PES2 using solid lines and dotted lines.Similar to FIG. At the boundary (on-cylinder), four-phase tracks are identified by selecting the pulse amplitude and phase with corresponding gates, as shown by the waveforms of zero points, .

FIG. 9 is an explanatory diagram showing the configuration of another embodiment of the present invention. In the conventional examples and embodiments described above, the position detection pulse was formed by a dibit pulse of both positive and negative polarities, whereas in this embodiment, a unipolar pulse was used, the clock was set to N, and the position detection pulse was set to S. , by detecting this with the servo head 20 and identifying it by polarity, it is possible to easily perform the same operation as the embodiment shown in FIG.

FIG. 10 shows an example of a detection circuit used in the head position signal detection method of the present invention.

In the figure, the position signal shown in FIG. 7 detected by the radial movement of the servo head 20 is
The gain is automatically adjusted by the AGC circuit 21,
Level differences due to the head or medium, or level differences between the outside and inside of the disk, etc. are compensated for.

This output is input to the gate generation circuit 22 and the peak amplitude detection circuit 23, and the gate generation circuit 22 detects the clock pulse in the position signal from the servo head 20, and uses a phase synchronization circuit etc. to select each position detection pulse. Create a gate pulse.

In the peak amplitude detection circuit 23, the gate creation circuit 2
Each position detection pulse is detected by the gate pulse from 2.
Detect the peak values of O1, E1, O2, and _E2 , and
Two types of position error signals are detected as _E1 = PES1 and V _O2 -V _E2 = PES2.

As an application example of the present invention, when it is desired to shift the phase of two types of position error signals by a half track pitch, the servo track width Tw on the servo disk surface is
By setting the width to 1/2 and setting the core width of the servo head to 1.5Tw, the purpose can be easily achieved.

As explained above, according to the present invention, the position detection signal is written to the servo track by repeating four detection pulses with different phases in the circumferential direction for each track every four tracks. The detection servo head has a core width that is wider than the binary value of the servo track width. This makes it possible to effectively identify the boundaries of the four tracks, and
Since the core width of the servo head is wide, the S/N ratio is good and it is less affected by other factors such as the medium. In particular, since the position detection pulse of the present invention does not need to be formed by repeating, a position signal with good linearity can be obtained without fear of amplitude fluctuations caused by this.

[Brief explanation of the drawing]

Figures 1 to 5 a and b are explanatory diagrams of the conventional system and its drawbacks, Figures 6 to 8 are diagrams that explain the system and principle of the embodiment of the present invention, and Figure 9 is an explanatory diagram of the method and drawbacks of the conventional example. A schematic explanatory diagram of an embodiment. FIG. 10 is an explanatory diagram of an example of a detection circuit used in an embodiment of the present invention. In the figure, 1 is a servo track, 20 is a servo head, 21 is an AGC circuit, and 22 is a gate creation circuit. , 23 indicates a peak amplitude detection circuit.

Claims (1)

[Scope of Claims] 1. In a head position signal detection method in which a head position detection signal is written on a predetermined surface of a plurality of disks of a magnetic disk device as a servo disk, and the head position is detected using the signal, the position detection signal is transmitted to each track. Four detection pulses with different phases in the circumferential direction are written to the servo track every four tracks, and it is confirmed that the servo head for position detection has a core width wider than twice the servo track width. Characteristic head position signal detection method. 2. The head position signal detection method according to claim 1, wherein two types of head position signals having different phases in the disk radial direction are obtained from the four position detection pulses.