Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1997-08-19
2001-05-29
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S025000
Reexamination Certificate
active
06239936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to information storage systems and, more particularly, to a method and apparatus for calibrating a thermal response of a magnetoresistive (MR) element employed in an information storage system.
BACKGROUND OF THE INVENTION
A typical data storage system includes a magnetic medium for storing data in magnetic form and a transducer used to write and read magnetic data respectively to and from the medium. A disk storage device, for example, includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute. Digital information is typically-stored in the form of magnetic transitions on a series of concentric, spaced tracks comprising the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors, with each sector comprising a number of information fields, including fields for storing data, and sector identification and synchronization information, for example.
The actuator assembly typically includes a plurality of outwardly extending arms with one or more transducers and slider bodies being mounted on flexible suspensions. A slider body is typically designed as an aerodynamic lifting body that lifts the transducer head off of the surface of the disk as the rate of spindle motor rotation increases, and causes the head to hover above the disk on an air-bearing produced by high speed disk rotation. The distance between the head and the disk surface, typically on the order of 50-100 nanometers (nm), is commonly referred to as head-to-disk spacing.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the transducer assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals, commonly referred to as read back signals, in the read element.
Conventional data storage systems generally employ a closed-loop servo control system for positioning the read/write (R/W) transducers to specified storage locations on the data storage disk. During normal data storage system operation, a servo transducer, generally mounted proximate the read/write transducers, or, alternatively, incorporated as the read element of the transducer, is typically employed to read information for the purpose of following a specified track (track following) and locating (seeking) specified track and data sector locations on the disk.
Within the data storage system manufacturing industry, much attention is presently being focused on the use of an MR element as a read transducer. Although the MR element would appear to provide a number of advantages over conventional thin-film heads and the like, it is known by those skilled in the art that the advantages offered by the MR element are not fully realizable due to the present inability of data storage systems to accommodate a number of undesirable MR element characteristics.
In particular, MR element transducers introduce a distortion in the sensed magnetic signal, which typically represents data or servo information stored on a magnetic storage disk. The distortion to the magnetic signal is caused by many factors, including a number of undesirable characteristics inherent in the MR element and the specific configuration and orientation of the MR element when incorporated into a transducer assembly. Notwithstanding such undesirable characteristics, the data storage system manufacturing community continues to expend resources to develop improved MR element transducers.
Several techniques have been developed to convert the magnetic signal induced in an MR element transducer to a spacing signal that varies as a function of head-to-disk spacing changes. For example, the magnetic spacing signal has been used in defect screening procedures in an effort to detect the presence of anomalous disk surface features. Such surface defects are typically associated with excessively large head-to-disk spacing changes or disk surface contact events.
In order to conduct a survey of a disk surface using such a conventional approach, magnetic information must first be written to the disk surface from which the magnetic spacing signal is subsequently produced. It is appreciated by those skilled in the art that writing magnetic information to a disk surface for purposes of conducting defect screening is a time consuming and costly process. By way of example, a conventional high capacity data storage system may include ten data storage disks, each of which has two data storing surfaces. Associated with each of the twenty data storing disk surfaces is an R/W transducer. Although twenty write elements may be used to write magnetic information to the twenty disk surfaces, such a conventional data storage system includes only a single write channel which must be multiplexed, or time-shared, across the twenty transducers. As such, the magnetic information is written to each of the twenty disk surfaces one surface at a time.
Assuming that each of the twenty data storing surfaces is formatted to include 6,000 tracks per inch (TPI), and the disks are rotated at a rate of 7,200 revolutions per minute (RPM), and further assuming typical delays associated with actuator and MR transducer positioning, it will take approximately one minute to write the magnetic information to each of the twenty data storing surfaces, or approximately twenty minutes to process all of the-twenty disk surfaces. Only after the magnetic information is written to the twenty disk surfaces can a conventional disk surface surveying procedure be performed.
Further, it is known that a magnetic spacing signal incorrectly indicates the presence of certain surface features, such as magnetic voids, as variations in the topography of a disk surface. Moreover, contact between the MR element and the disk surface can result in wearing of the magnetic film provided on the disk surface, thereby producing a magnetic void at the abraded disk surface location.
There exists a keenly felt need in the data storage system manufacturing community for an apparatus and method for reducing the cost and time currently expended when conducting a survey of a disk surface using an MR element transducer. There exists a further need to provide such an apparatus and method which is not compromised by the undesirable characteristics inherent in an MR element transducer. The present invention is directed to these and other needs.
SUMMARY OF THE INVENTION
The present invention generally provides a method and apparatus for calibrating a thermal response of an magnetoresistive (MR) element. The disclosed calibration technique may, for example, be used for the detection of surface defects on a storage medium.
In accordance with one embodiment of the invention, a thermal spacing signal is read using an MR element spaced apart from a surface of a moving storage medium. From the thermal spacing signal,a signal value and calibration value are produced. Using the signal value and the calibration value,a calibrated signal value is produced. The calibration value may, for example, be indicative of the surface roughness of a portion of the storage medium over which the MR element traverses and the signal value may, for example, be indicative of the largest bump on the surface of the portion of the storage medium. The calibrated signal value may, for example, be compared against a pre-determined threshold to detect surface defects on the storage medium.
In accordance with one aspect of the invention, the thermal spacing signal is a signal induced in the
Abraham David William
Chainer Timothy Joseph
Etzold Karl-Friedrich
Ottesen Hal Hjalmar
Smith Gordon James
Hollingsworth Mark A.
Hudspeth David
International Business Machines - Corporation
Merchant & Gould P.A.
Wong K.
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