High Data Rate Erasable Magneto-Optic Media Tester

Abstract

A portable highly stable air bearing magneto-optic tester is described that has been used to evaluate first and second surface media. The system was designed to handle 14 and 12 inch diameter disks with inner diameter holes similar to magnetic disks. Disk substrates made of glass, plastic, or aluminum can be tested at spin rates in the range of 200 to 3600 RPM. Two electromagnets are built into the tester. One is used to saturate the media and another to supply the write and erase field. A single optical head is used to write and read out data. The disk drive system is built of heavy aluminum plates in the form of a compact cage. An air bearing spindle driven by a brushless dc motor is used to spin the disk. The disk runs over the optics module in an inverted configuration selected to minimize the problem of dust settling on first surface media and to provide the means of working with smaller diameter disks. An air bearing slide is used to move the optical head. This slide is driven by a Compumotor stepper motor through a precision V-nut and screw. The stepper motor and controller combination can achieve a resolution of 1/20 micrometer per step. The stability of the media tester with glass disks is such that it can sit on a written one micrometer wide track for onver 30 minutes without noticing any degrading effect on the output signal.