Slider-Disk Clearance Measurements in Magnetic Disk Drives Using the Readback Transducer

Abstract

A new method is described for noninvasively mea- suring the mechanical clearance between a recording head slider and the magnetic medium in hard-disk drives. The method is based on the detection of the pulse width of the read transducer output. A variation in clearance produces a proportional variation in pulse width. The proportionality factor can be determined by simulating the spacing loss using a digitized isolated impulse, typical for the respective head-disk combination. Instrumentation is presented that provides an output voltage proportional to the ratio {pwr/t) of the pulse width at x% of the peak amplitude PWx and the period T of the readback signal. This instrumentation measures the absolute slider-disk clearance by evacuating the air from the disk drive. The bandwidth is such that clearance dynamics can also be measured. This allows clearance measurements as well as the detection of undesirable slider-disk interactions, in situ, in fully operational disk drives. © 1994 IEEE. All right reserved.