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Abstract

An optical servo head and method for reading position information on a medium, such as a magnetic disk, having a plurality of optical servo tracks in the form of relatively nonreflective regions on a reflective surface of the medium. With a magnetic disk, the nonreflective regions comprise concentric grooves etched in the disk surface and the reflective regions comprise the land areas between the grooves. The optical servo head is mounted on a carriage/head assembly of a disk drive and comprises an infrared light emitting diode, a collection lens, a routing mirror and a multicell photodetector. The method of reading position information from the magnetic disk comprises the steps of illuminating the disk with the infrared diode, focusing the image of the optical tracks on the cells of the photodetector such that a linear signal will be generated as the optical tracks pass the photodetector cells, and generating a continuous output signal from the photodetector cell output which is used to control the positioning of the carriage/head assembly. The output signal can be directed through a synchronous detection circuit to improve the S/N contrast between the reflective and nonreflective areas. Additionally, the output signal can be routed to an alignment circuit comprising a pair of digital-to-analog converters, a pair of digital signal generators, an adder and an electronic filter and which electronically compensates for imprecision in the servo head-data head separation distance. Track sweeping without leaving the position loop is also accomplished through use of the alignment circuit.

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