HP Labs Technical Reports
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Track Linearity Measurements of DDS Helical-Scan Data Recorders
Abstract: This paper presents the method used to measure and adjust Hewlett-Packard s DDS helical-scan tape recorders so that the recorded tracks deviate from a straight line inclined at 6.3776 degrees by less than 5 microns over their 23.5 mm length. The shape of the recorded tracks is primarily determined by the adjustment of various guide pins. The adjustment is performed in real-time while the mechanism reads a magnetically encoded position sensing tape which has a resolution better than 0.040 microns. These tapes are themselves recorded on ordinary production mechanisms but are calibrated by decorating the magnetic tracks with a ferrofluid to make them visible. They are then calibrated optically using a correlation based algorithm with an accuracy of 0.100 microns.
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