Slider-disk clearance measurements in magnetic disk drives using the readback transducer

Abstract

A new method id described for non-invasively measuring the mechanical clearance between a head slider and the recording medium in magnetic storage devices. The method is based on detection of the pulse width of the output signal of the readback transducer (read head). It is shown that a variation in clearance produces a proportional variation in pulse width. The proportionality factor (measurement sensitivity) can be determined by simulating the effect on the (varying) spacing loss on a digitized isolated impulse response typical for the head-disk combination under investigation. Instrumentation is presented that provides an analogue output voltage which is a measure for the ratio (PWx/T) of the pulse width at the x% level (PWx) and the repetition period (T) of the readback signal. With this instrumentation the absolute slider-disk clearance can be determined by evacuating the air from the head-disk interface (pump down). The bandwidth (0 -125 kHz) of the instrumentation is such that clearance dynamics can also be measured. This allows the detection of glide defects (undesirable slider-disk interactions), in situ, in a fully operational storage device. Examples of these clearance and glide measurements are given for hard disk drives.