Robust servo demodulation filtering method

Details Robust servo demodulation filtering method Robust servo demodulation filtering method

2001-03-30

2004-01-13

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S029000, C360S030000, C360S039000

Reexamination Certificate

active

06678110

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods for determining a transducer head position in a mass storage system, and more particular to systems for accurately interpreting positional information received from transducer heads.
BACKGROUND OF THE INVENTION
Information handling systems have undergone explosive growth over the past several years. New technologies are allowing today's common components to outperform state-of-the-art components of five years ago. In disc drives, for example, areal density has doubled each year for the past several years. This has been made possible, in part, by the development of better transducers than previously existed. Not surprisingly, most modern transducers are highly sophisticated and temperamental.
Most modern disc drives include one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in many thousands of concentric circular tracks by an array of transducers mounted to a radial actuator for movement of the transducers relative to the discs. Typically, such radial actuators employ a voice coil motor to position the transducers with respect to the disc surfaces. Sliders carrying the transducers are mounted via flexures at the ends of arms which project radially outward from a rotary actuator body. The actuator body pivots about a shaft mounted to the housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the transducers each move in a respective plane parallel with the surfaces of the discs.
The actuator voice coil motor includes a coil mounted on the side of the actuator body opposite the transducer arms so as to be immersed in the magnetic field of an array of permanent magnets. When controlled DC current is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnets and causes the coil to move in accordance with the well-known Lorenz relationship. As the coil moves relative to the magnets, the actuator body pivots about the pivot shaft and the transducers are moved across the disc surfaces.
Typically, the transducers are supported over the discs by actuator slider assemblies which include air-bearing surfaces designed to interact with a thin layer of moving air generated by the rotation of the discs, so that the transducers are said to “fly” over the disc surfaces. Generally, the transducers write data to a selected data track on the disc surface by selectively magnetizing portions of the data track through the application of a time-varying write current to the transducer. In order to subsequently read back the data stored on the data track, the transducer detects flux transitions in the magnetic fields of data track and converts these to a signal which is decoded by read channel circuitry and servo channel circuitry.
Transducers in other data storage systems operate differently, but many are similarly vulnerable to mechanical disturbances or other noise sources. Existing methods of determining a transducer position rely upon retries and error correction methods that may not be effective alone. Without accurate position detection, accurate positioning is often impossible. These noise sources can thus cause performance losses and user data recovery failures. Thus, there is a need for more effective approaches to determining transducer head position accurately.
SUMMARY OF THE INVENTION
The present invention is a robust and efficient method for determining the location of a transducer head in a mass storage system. A position-indicative signal characterized by a fundamental frequency F is received from a data path including the transducer head. Energy in the signal at frequencies smaller than F/10 is substantially attenuated by a special filter, which may be an analog or digital differentiator. (As used herein, an attenuation is “substantial” if it reduces a signal component by several decibels or more.) A sequence of bits indicative of the transducer head position is then extracted from the digitized, filtered signal.
Other features and advantages of the present invention will become apparent upon a review of the following figures and their accompanying description.


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