Patent ID: 8804275

Claim:
A method for determining head-disk contact in a magnetic recording disk drive having 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 rotating disk, a write head on the slider, a head-disk spacing sensor, 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: signaling the fly-height actuator to move the write head toward the disk as the disk is rotating; detecting an output signal from the spacing sensor at a fundamental frequency corresponding to the frequency of topographic regions detected by the spacing sensor; filtering the spacing sensor output signal to detect at least one of the second and higher harmonic frequencies; identifying an inflection point in the detected at least one harmonic frequency; and recording the fly-height actuator control signal corresponding to said inflection point value as the fly-height control signal head-disk contact (HDC) value.