Seagate Technology Incorporated

Alan Choon Tan

Myint Ngwe

Beng Wee Quak

Joseph C Liu

Bernard Tuang Lim

Head disc interference is detected and analyzed using the standard deviation of read back signal frequency. First, the amount of longitudinal head oscillation affecting transducer read/write heads located in the hard drive is measured. Measuring the longitudinal head oscillation is achieved by determining the degree of frequency modulation associated with the read-back signal as compared with a constant frequency used to write the information. Second, this measured amount of oscillation is compared to a predefined threshold value. Finally, a head disc interference alarm is activated when the oscillation is greater than the defined threshold value.

Drive in-situ head disc interference detection using standard deviation

A method and apparatus for detecting and measuring head-disc interference, in a disc drive, for the purpose of taking preventative and corrective measures, to prevent disastrous head crashes and permanent data loss, is disclosed. The method and apparatus detect and measure the frequency modulation (FM) of a read back signal generated by longitudinal head oscillation, as a result of head-disc interference. The longitudinal head oscillation can be ascribed to the non-linear response of the air bearing supporting the head on the disk surface. The response exhibits a vibration frequency in the head in the 100 to 250 kHz range. The more severe the interference contact is, the higher the vibration amplitude which then leads to read signal frequency modulation (FM). A method and apparatus is described to detect the FM modulation and thereby to detect the severity of the head disk interference for proximity recording. A pre-written pattern on the disk can be read back to monitor for FM, and a modulation index, .beta., is generated by observing the resulting signal. By demodulating the modulated read back signal, the severity of the interference can be determined. This method can be applied as a diagnostic tool at a manufacturing test station, in a laboratory test setup, or in a disk drive using the disk drive's own read/write channel electronics, without the need for an external sensor.

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Singapore, Singapore

Alan Choon Tan