Optical methods of the head positioning in magnetic disk systems

This paper reports a new method of head positioning by applying optics to magnetic disk systems. To increase the accuracy of head positioning, several methods in which a servo disk is not used have been investigated. Until now these methods were unsuccessful because of interference between the head positioning signal and the data signal, both of which were recorded on the same data surface. In the method explained here, the head can be positioned on the disk by an optically detected positioning signal without disturbing operation of the magnetic disk system. A unique structure for both the disk and head was investigated. Optical patterns depicting position of the data tracks were formed by coloring the anode oxidized surface layer of an aluminum substrate, and by forming a magnetic film over that. Three optical fibers were imbedded in a hole in the central rail of a Winchester-type ferrite head and were used to read the optical pattern. A stable positioning signal was optically detected from the rotating disk. By using the signal to assemble a simple servo loop, the head could be positioned with ±3 μm accuracy. Potential accuracy was found to be ±0.7 μm.