System and method for calibrating and controlling a fly-height actuator in a magnetic recording disk drive
View Patent ↗A system and method for calibrating and controlling a magnetic recording disk drive fly-height actuator uses the signal from the magnetoresistive (MR) read head to determine head-disk contact (HDC). The MR signal is measured over a low-frequency range, with the slider out-of-contact with the disk, to develop a reference value. The MR signal is then measured over the same low-frequency range and if it exceeds the reference value by some predetermined amount, this is an indication of HDC. The fly-height actuator control signal value for HDC is recorded and thus corresponds to a head-disk spacing of zero. The calibration method also determines the sensitivity of head-disk spacing to the fly-height actuator control signal by measuring a series of MR read signal amplitudes for a corresponding series of control signals. The fly-height actuator is calibrated from the sensitivity and the value of control signal that results in zero head-disk spacing, and can then be controlled to move the head to a desired fly height and maintain it at the desired fly height.
1. A method for calibrating a fly-height actuator in a magnetic recording disk drive having a rotatable magnetic recording disk, an air-bearing slider maintained near the surface of the rotating disk, a read/write head on the slider, a digitizer for digitizing the signal from the read head, a head fly-height actuator for changing the head-disk spacing, and a fly-height controller connected to the fly-height actuator, the method comprising:
determining the fly-height control signal head-disk contact (HDC) value, comprising (a) integrating the amplitude of the digitized read-head signal over a predetermined frequency range when the slider is out of contact with the surface of the rotating disk to determine a reference value; (b) applying a control signal to the fly-height actuator to reduce the head-disk spacing; (c) integrating the amplitude of the digitized read-head signal over said predetermined frequency range as a measured value as the head-disk spacing is reduced; and (d) when said measured value is greater than said reference value by a predetermined amount, recording the fly-height actuator control signal as said HDC value;
measuring, for a series of fly-height control signal values, a corresponding series of digitized read-head signal amplitudes;
calculating head-disk spacing from said measured read-signal amplitudes; and
correlating changes in head-disk spacing with changes in fly-height actuator control signal value.
2. The method of claim 1 wherein said predetermined frequency range is between about 0.1 and 2 MHz.
3. The method of claim 1 wherein the head fly-height actuator is located on the slider and is one of a thermal actuator, an electrostatic actuator and a piezoelectric actuator.
4. The method of claim 1 wherein correlating changes in head-disk spacing with changes in fly-height actuator control signal value comprises:
calculating a generally linear function of head-disk spacing to fly-height actuator control signal value, the slope of said linear function being the change in head-disk spacing with change in fly-height actuator control signal value.
5. The method of claim 4 wherein said linear function is represented generally by the following relationship:
d =(ρ)[ Hp ( HDC )− Hp ( d )],
where d is the head-disk spacing, ρ is the slope of the linear function, Hp(HDC) is the fly-height control signal HDC value, and Hp(d) is the fly-height control signal value corresponding to a head-disk spacing of d.
6. The method of claim 5 wherein the head fly-height actuator is a thermal actuator comprising a heater located on the slider near the head and wherein Hp is heater power.
7. The method of claim 5 further comprising, after calculating said generally linear function, controlling the fly-height actuator by applying a control signal value of Hp(Dc) to maintain the head-disk spacing substantially at a desired value Dc.
8. A method for controlling the head-disk spacing in a magnetic recording disk drive having a rotatable magnetic recording disk, an air-bearing slider maintained near the surface of the rotating disk, a read/write head on the slider, a digitizer for digitizing the signal from the read head, a head fly-height actuator for changing the head-disk spacing, and a fly-height controller connected to the fly-height actuator, the method comprising:
determining the fly-height control signal head-disk contact (HDC) value, comprising (a) integrating the amplitude of the digitized read-head signal over a predetermined frequency range when the slider is out of contact with the surface of the rotating disk to determine a reference value; (b) applying a control signal to the fly-height actuator to reduce the head-disk spacing; (c) integrating the amplitude of the digitized read-head signal over said predetermined frequency range as a measured value as the head-disk spacing is reduced; and (d) when said measured value is greater than said reference value by a predetermined amount, recording the fly-height actuator control signal as said HDC value;
determining the sensitivity of head-disk spacing to fly-height control signal value, comprising measuring a series of digitized read-head signal amplitudes for corresponding fly-height control signal values; and thereafter
controlling the head-disk spacing to a desired spacing by use of the previously determined HDC value and sensitivity.
9. The method of claim 8 wherein said predetermined frequency range is between about 0.1 and 2 MHz.
10. The method of claim 8 wherein the head fly-height actuator is located on the slider and is one of a thermal actuator, an electrostatic actuator and a piezoelectric actuator.
11. The method of claim 8 wherein the head fly-height actuator is a thermal actuator comprising a heater located on the slider near the head and wherein the fly-height control signal is heater power (Hp).
12. The method of claim 11 further comprising calculating, from the measured series of digitized read-head signal amplitudes and corresponding fly-height control signal values, a generally linear function of head-disk spacing to Hp, the slope of said linear function being said sensitivity of head-disk spacing to Hp, said linear function being represented generally by the relationship:
d =(ρ)[ Hp ( HDC )− Hp ( d )],
where d is the head-disk spacing, p is the slope of the linear function, Hp(HDC) is the fly-height control signal HDC value, and Hp(d) is the fly-height control signal value corresponding to a head-disk spacing of d.
13. A system for calibrating a magnetic recording disk drive fly-height actuator comprising:
a rotatable magnetic recording disk;
an air-bearing slider maintained near the surface of the disk when the disk is rotating;
a read/write head on the slider;
a fly-height actuator for changing the spacing between the read/write head and the disk surface;
an analog-to-digital converter for digitizing the signal from the read head;
a digital signal processor for processing the digitized signal from the read head and for sending control signals to the fly-height actuator; and
a program of instructions readable by the processor for undertaking method acts comprising
(a) determining the fly-height control signal head-disk contact (HDC) value by (i) integrating the amplitude of the digitized signal over a predetermined frequency range when the slider is out of contact with the surface of the rotating disk, (ii) recording said integrated out-of-contact signal as a reference value, thereafter (iii) integrating the amplitude of the digitized signal over said predetermined frequency range as a measured value, and (iv) when said measured value is greater than said reference value by a predetermined amount, recording the fly-height actuator control signal as said HDC value; and
(b) determining the sensitivity of head-disk spacing to fly-height control signal value by (i) measuring, for a series of fly-height control signal values, a corresponding series of digitized read-head signal amplitudes, (ii) calculating head-disk spacing from said measured read-signal amplitudes, and (iii) correlating changes in head-disk spacing with changes in fly-height actuator control signal value.
14. The system of claim 13 wherein the method act of correlating changes in head-disk spacing with changes in fly-height actuator control signal value comprises:
calculating a generally linear function of head-disk spacing to fly-height actuator control signal value, the slope of said linear function being the change in head-disk spacing with change in fly-height actuator control signal value.
15. The system of claim 14 wherein the method act of calculating a generally linear function comprises calculating a linear function represented generally by the following relationship:
d =(ρ)[ Hp ( HDC )− Hp ( d )],
where d is the head-disk spacing, p is the slope of the linear function, Hp(HDC) is the fly-height control signal HDC value, and Hp(d) is the fly-height control signal value corresponding to a head-disk spacing of d.
16. The system of claim 15 wherein the head fly-height actuator is a thermal actuator comprising a heater located on the slider near the head and wherein Hp is heater power.
17. The system of claim 15 wherein said program of instructions readable by the processor includes the method act of controlling the fly-height actuator by applying a control signal value of Hp(Dc) to maintain the head-disk spacing substantially at a desired value Dc.
18. The system of claim 13 wherein the fly-height actuator is one of a thermal actuator, an electrostatic actuator and a piezoelectric actuator.
19. The system of claim 13 wherein the system is a head/disk tester.
20. The system of claim 13 wherein the system is a magnetic recording disk drive.