Method of measuring the read-to-write offset in a disc drive...

Details Method of measuring the read-to-write offset in a disc drive... Method of measuring the read-to-write offset in a disc drive...

1995-12-21

2002-11-19

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S075000

Reexamination Certificate

active

06483658

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is a method of measuring the read-to-write offset in a disc drive system having separate read and write elements. More specifically, the present invention is a method of measuring the read-to-write offset by measuring read errors as a function of incremental offset within a track.
In the prior art, a disc drive head was typically comprised of a single thin film transducer, which performed both read and write functions. As the state of disc drive design evolved, track widths became narrower. It has became increasingly difficult to combine the read and write functions in a single thin film transducer. Accordingly, disc drive designers began to use separate read and write elements. Typically, the write element was comprised of a thin film transducer optimized to perform the write function. The read element typically comprised a magnetoresistive (MR) sensor. The MR sensor was formed from a strip of magnetoresistive material, typically Permalloy, which had a resistance which varied with the magnitude of flux passing through the sensor. The MR sensor was optimized to perform read functions, and was usually narrower than the write element.
Because the read and write elements cannot occupy the same physical space, a gap exists between the two elements. In a disc drive having a linear actuator, the effect of the gap can be minimized because the two elements can be placed in-line, and will remain in-line for every track on the disc surface. However, linear actuators are rarely used in modern disc drives because they are slower, require more space, and are not as precise as rotary actuators.
Most newer disc drives employ a rotary actuator. A rotary actuator includes an arm which is rotatably mounted to traverse an arc across the disc surface. Because the arm traverses an arc, the gap between the read and write elements results in a read-to-write offset. While the read and write elements might in-line for a single track, they typically will not be in-line for other tracks on the disc surface.
Accordingly, it is desirable to have a method for measuring and managing the read-to-write offsets for every track on disc drive surface and every pair of read and write elements in a disc drive system.
SUMMARY OF THE INVENTION
The present invention is method for measuring the read-to-write offset of a track on a disc drive system having a transducer with separate read and write elements. An “error bucket” is mapped, and actuator offsets are determined from the error bucket. The read-to-write offset is determined from the difference between the center of the error bucket and the offset at which the track was written.
In one form of the present invention, the read-to-write offset of all tracks accessed by a transducer can be calculated from a single measured read-to-write offset. In other forms of the invention, the read-to-write offsets of additional tracks are measured.


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