Excel Precision Corporation

Mervyn L Hopson

John C Tsai

Hubert Song

Kam-Fung Yan

Jean Chi

A servotrack writing apparatus (10) for use on computer disk drive workpieces (12). A writer controller (58) puts the writing apparatus (10) in the role of master to direct the workpiece (12) as a slave to position its read-write head (36) and to write the servotracks. A tracking section (54) provides a modulated light beam (72) from which a reflected portion is detected by a bi-cell photo sensor (70) and processed in the writer controller (58) to determine the position of a thru-hole (40) or a detection region (42) in the actuator arm (24) of the workpiece (12). The writer controller (58) may use a lock-in amplifier (102, 104) for the processing the reflected portion of the light beam (72). A reference arm (44) is locked and moved in a synchronous relationship with the actuator arm (24). A measurement section (56) determines the position of the reference arm (44), and may include an interferometer system (122) having a differential head (128) and a differential target (124), to permit increased resolution and nulling of errors. The interferometer system (122) may also use multiple frequency techniques to further increase resolution.

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Cupertino, CA, United States of America

Mervyn L Hopson