Development of Head Flying Height Measuring Apparatus Using Image Processing

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A novel head-disk spacing measurement system based on Michelson laser interferometry has been developed. This system was comprised of four kinds of sub-systems: interference optical instrument, high-vision (200 million pixels) image capturing device, fringe following mechanism/circuits and disk rotation mechanism. Image processing for high-vision image operable on the Window system and a multiple fringe following technique permitted high reproducibility and high accuracy. The fringe following is the way in which interference light beam is divided into two beams: one is for CCD and the other is for PSD (Position Sensitive Detector). The output of PSD is applied to a PZT actuator to derive a reference mirror such that the fringe on CCD maintains a fixed position. Using this system, dynamic behavior of a contact-type head slider while starting was successfully clarified. Next, the fringe following technique was dualized in order to fix two fringe parameters, the position and inclination of the fringe, or the position and interval between the fringes. In this technique, the reference mirror and PZT actuator were separated into two sets, one is for parallel displacement and the other is for pitching inclination. This enabled us to fix the fringe image more accurately and thus followed to accurate ridgeline extraction after multiple image processings. Finally, the multiple fringe following technique were extended to an online measurement of two-dimensional attitudes of the target plane utilizing the fact that the output signals from PSDs were reflection of the motion of the target plane.