Rangeless servo notch optimization

Abstract

A method for placing a predetermined number of notch filters in a disc drive servo control system to attenuate noise frequencies, in order of decreasing resonance magnitudes, is disclosed. The method involves calculating an open loop response for a response spectrum of the drive, calculating a notch filter for any noise frequency that exceeds a threshold, mathematically applying the notch filter into the servo control system, recalculating the open loop response and applying another filter for a noise frequency that exceeds the threshold and repeating until no noise frequencies exceed the gain threshold; selecting another frequency range and repeating the same process until a predetermined number of notch filters has been placed in the servo control system.

Description

RELATED APPLICATIONS[0001]This application claims priority of U.S. provisional application Ser. No. 60 / 347,593, filed Jan. 11, 2002.FIELD OF THE INVENTION[0002]This application relates generally to data storage device servo control systems and more particularly to a method for optimizing notch filter placement in a servo control system such as is typically used in a disc drive to control positioning of a transducer over a rotating storage medium.BACKGROUND OF THE INVENTION[0003]Notch filters are placed in the track following and seeking control loops in conventional servo control systems to help stabilize the actuator mechanics. These notch filters are typically mathematically implemented in algorithms defined in the drive control firmware. The particular placement parameters utilized in these notch filter algorithms may be stored in the boot record on the disc or permanently stored in the firmware. To compensate for drive-to-drive variations, notch filter placement is customized fo...

AI Technical Summary

Benefits of technology

[0006]Against this backdrop the present invention has been developed. The rangeless SNO method in accordance with the present invention essentially works by creating a circular memory buffer within the SNO process. The buffer length is preferably equal to the allotted memory in the factory test system. At each frequency point contained in the memory buffer, the SNO algorithm measures the structural and compensator responses of the drive, mathematically computes the open loop response, and compares the output to a gain threshold. If the open loop response exceeds the gain threshold, a peak detect algorithm finds the resonance peak, determines the required filter parameters for this peak, and places a notch filter centered on the resonance. Once placed, the notches are mathematically applied to all frequency points in the memory buff

Problems solved by technology

Due to memory limitations, the factory test systems that perform this portion cannot acquire the necessary number of data points to optimize the entire frequency range of interest in disc drive operation.

First, it requires prior identification of the resonances that will require notch filters.

Third, as previously mentioned, the SNO process only allows for one notch per range.

The current conventional SNO process is inadequate, due to drive-to-drive frequency variations and the one notch per sub-range limitation, in the case of double peaked resonances that require two notches for appropriate coverage.