System and method for determining head-disk contact in a magnetic recording disk drive having a fly-height actuator

A system for detecting head-disk contact in a magnetic recording disk drive having a fly-height actuator comprising:

• a rotatable magnetic recording disk having a plurality of generally equally angularly spaced topographic regions extending across the 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 head-disk spacing sensor responsive to changes in spacing between the slider and the disk and capable of providing an output signal at a frequency corresponding to the frequency of topographic regions when the disk is rotating;
• a harmonic frequency detector for detecting, from the head-disk spacing sensor output signal, at least one of the second and higher harmonic frequencies of topographic regions when the disk is rotating;
• a fly-height actuator for changing the spacing between the read/write head and the disk;
• and
• a digital processor configured to signal the fly-height actuator to move the read/write head toward the disk as the disk is rotating, process the signal from the harmonic frequency detector, identify an inflection point of the signal from the harmonic frequency detector, and record the fly-height actuator control signal corresponding to said inflection point as the fly-height control signal head-disk contact (HDC) value.

A magnetic recording disk drive comprising:

• a rotatable bit-patterned media (BPM) magnetic recording disk having a plurality of generally equally angularly spaced servo sectors extending generally radially across the disk, the servo sectors having a topography different from the topography of non-servo sector regions of the 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 thermal head-disk spacing sensor on the slider responsive to changes in spacing between the head and the disk and capable of providing an output signal at a frequency corresponding to the frequency of servo sectors when the disk is rotating;
• an analog-to-digital converter (ADC) for digitizing the spacing sensor output signal;
• a thermal fly-height actuator on the slider for changing the spacing between the read/write head and the disk;
• machine-readable memory containing a program of instructions;
• and
• a digital processor capable of reading and executing the program of instructions, the processor being configured to signal the fly-height actuator to move the read/write head toward the disk as the disk is rotating, digitally filter the digitized spacing sensor output signal to pass at least one of the second and higher harmonic frequencies, identify an inflection point in the filtered at least one of the second and higher harmonic frequencies, and record the fly-height actuator control signal corresponding to said identified inflection point as the fly-height control signal head-disk contact (HDC) value.