Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1998-06-23
2001-03-20
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S076000, C360S029000, C360S077080
Reexamination Certificate
active
06204991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a head position signal demodulator and a head positioning unit utilizing the demodulator, and more particularly to a head position signal modulator which generates a position signal of the head from a servo pattern and outputs the signal, and a head positioning unit utilizing the demodulator, in a magnetic disk unit which positions a magneto-resistance effect head by a rotary actuator.
2. Description of the Related Art
There is a type of a magnetic head where a record head and playback head are equipped at a specified interval along the tangential direction of a disk. For the playback head, a magneto-resistance effect head (MR head) is frequently used, and for the record head, an inductive head (ID head) is used. A magnetic disk unit has a type which positions a magnetic head in such a configuration by a rotary actuator. In this case, an inclination in the disk tangential direction occurs to the magnetic head depending on the position of the magnetic head on the disk. Because of this, a locus of the record head during recording and a locus of the playback head during playback may not match even if the magnetic head is scanning the same track. This is not good for regenerating data. Ideally the locus of the record head during recording and the locus of the playback head during playback should match.
Micro jogging is used for this control. Micro jogging is an operation for delicately adjusting the position of the magnetic head for recording and for playback, so that the locus of the record head during recording and the locus of the playback head during playback match on the same track. The magnetic head is positioned by regenerating a servo pattern which has been recorded on the magnetic disk, and controlling the actuator so that a position signal of the magnetic head which is generated according to the playback signal is maintained at a constant level. If micro jogging is performed here, the position where the magnetic head is supposed to be positioned differs for recording and for playback. Therefore in prior art, a value of the position signal to be maintained is different for recording and for playback.
This means that in a positioning control system, a control target value must be switched for recording and for playback, which made the configuration of the control system complicated. Also the relationship between the correction amount by micro jogging and the change of the position signal had to be measured for presetting the control target, which increased the number of manufacturing processes. An MR head also has such problems as thermal aspirity (TA), Barkhausen noise (BHN), baseline shift (BLS), asymmetric waveform (WA), output value fluctuation (PCOV), and asymmetric off track profile, and these problems sometimes interfere with the correct playback of servo patterns.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to fix the value of the position signal even after micro jogging, so that the positioning control system can control positioning with the same control target value all the time.
Another object is to simplify the configuration of the positioning control system by fixing the value.
Another object is to generate a correction position signal even if a servo pattern could not be regenerated correctly due to a problem of the MR head.
As a consequence, in accordance with the present invention, a head position signal demodulator that demodulates a position signal indicating the position of the magnetic head in the disk radius direction based on a servo pattern recorded on the magnetic disk, comprises: a waveform shaping circuit which shapes an input signal obtained from the magnetic head according to the servo pattern; a phase comparison circuit which compares a phase of an output signal of the waveform shaping circuit and a phase of a reference signal. and outputs a phase difference signal. The head position signal demodulator also includes a position signal generation circuit that generates a position signal of the magnetic head based on the phase difference signal, and a phase shifter which changes the phase of the reference signal during micro jogging, for an amount of the phase which has been set according to the amount of the micro jogging.
Here the waveform shaping circuit may include a band pass filter.
The waveform shaping circuit may include a positive side shaping circuit which extracts and shapes the positive side waveform of an input signal obtained from the magnetic head according to the servo pattern, and a negative side shaping circuit which extracts and shapes the negative side waveform of the input signal obtained from the magnetic head according to the servo pattern. In this case, the phase comparison circuit comprises a positive side comparison circuit which compares the phase of an output signal of the positive side shaping circuit with the phase of a positive side reference signal and outputs a phase difference signal, and a negative side comparison circuit which compares the phase of an output signal of the negative side shaping circuit with the phase of a negative side reference signal and outputs a phase difference signal. The position signal generation circuit includes a synthesizer which synthesizes an output signal of the positive side comparison circuit and an output signal of the negative side comparison circuit. The waveform shaping circuit may include a pulsing circuit which converts an input signal obtained from the magnetic head into pulses, and a ½ dividing circuit which converts an output signal of the pulsing circuit to a pulse signal with ½ frequency and 50% duty.
The phase comparison circuit may include a reference oscillator which outputs the positive side reference signal, and a 90° phase shifter which changes a phase of an output signal of the reference oscillator 90° to be the negative side reference signal.
The positive side shaping circuit may include a positive side detection circuit which extracts the positive side waveform of an input signal obtained from the magnetic head, and a positive side pulsing circuit which converts an output signal of the positive side detection circuit into pulses.
A positive side ½ dividing circuit which converts an output signal from the positive side pulsing circuit to a pulse signal with ½ frequency and 50% duty and outputs the pulse signal may also be included. The negative side shaping circuit, on the other hand, may include a negative detection circuit which extracts the negative waveform of an input signal obtained from the magnetic head, and a negative side pulsing circuit which converts an output signal of the negative side detection circuit into pulses. A negative side ½ dividing circuit which converts an output signal from the negative side pulsing circuit to a pulse signal with ½ frequency and 50% duty and outputs the pulse signal may also be included.
The servo pattern may include the first field and third field which has recorded phase patterns where a phase shifts with the &pgr;/4 deviation in the disk tangent direction each time ¼ of one track pitch shifts in the disk radius direction, and the second field which has recorded phase patterns where a phase shifts with the &pgr;/4 deviation in the opposite direction from the first and third fields each time ¼ of one track pitch shifts in the disk radius direction. The waveform shaping circuit may include a positive side shaping circuit which extracts the positive side waveform of an input signal obtained from the magnetic head according to the servo pattern and shapes the positive side waveform, and a negative side shaping circuit which extracts the negative side waveform of the input signal obtained from the magnetic head according to the servo pattern and shapes the negative side waveform. In this case, the phase comparison circuit comprises a positive side comparison circuit which compares the phase of an output signal of the positive side shaping circuit wi
NEC Corporation
Sniezek Andrew L.
Wong K.
Young & Thompson
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