Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-12-04
2003-07-29
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
Reexamination Certificate
active
06600312
ABSTRACT:
RELATED PATENT APPLICATION The present patent application claims priority from a German application Application No. 01100791.1, filed on Jan. 13, 2001.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to direct access storage devices in general, and in particular to magnetic and optical storage devices. Still more particularly, the present invention relates to a method and apparatus for indexing hard disks by means of a scanning probe.
2. Description of Related Art
Severe performance problems on magnetic storage media may be caused by mechanical/magnetic defects, thickness variations of layering sequence or variations in magnetic coupling in or on top of the magnetic layers in the nanometer range of the magnetic storage media. Hence, certain techniques that enable the mapping of surface and magnetic properties of those critical areas (or areas of interest) with a very high spatial resolution are required. In addition, those techniques should be applicable in-situ in order to detect and characterize the cause of failures. Furthermore, those techniques should be incorporated within a test routine that allows critical areas to be characterized in a relatively short time frame.
One prior art approach for imaging hard disk defects is by characterizing a hard disk on a spin stand (SPST). With such approach, the magnetic and/or topographic properties of a spinning hard disk is analyzed by using test heads such as read write heads that are commonly used in hard disk drives. Some test heads may be specifically designed for test procedures that feature higher resolution, bandwidth, or cover larger tested areas. Defects on a nanometer scale detected by an SPST analysis can be mapped by a scanning probe microscope that is attached separately to the SPST. For even higher accuracy, the common co-ordinate system given by a rotating spindle on which the storage media are mounted can be used. One requirement for such test technique is that the storage media is stationary during both the writing process and the positioning process. Otherwise, the common co-ordinate system between the two measuring schemes will be lost. In other words, any deviation between the center of rotation and the center of the circular data tracks cannot be tolerated. Sometimes, such deviations may even be caused by removing a disk from the spindle and then placing the same disk back on the spindle again. Consequently, data or servo information in the storage media have to be deleted or overwritten by the test mechanism.
However, it is often not very convenient to overwrite additional magnetic information to hard disks because that would change the existing magnetic domains (or magnetic transitions) in the hard disk that might be the cause of performance problems. Another drawback of the above-mentioned overwriting approach is that, in some cases, failures of the magnetic media or magnetic failures can only be detected in a hard disk drive after a servo pattern has been written. Therefore, a nanometer level precision analysis of magnetic media as they come from the hard disk drive are very desirable. A mechanism or tool that is capable of using the existing magnetic transitions, such as the tracks of servo pattern, for exact positioning of the scanning probe is also very desirable.
Another prior art approach relies on magnetic marking techniques and detection of marked areas under an optical microscope. A typical magnetic marking technique is by using a ferrofluidic liquid that is brought on top of the magnetic media. Disadvantages of such approach include additional optical devices and many different analyzing steps are required and time consuming. In addition, not all defects can be found under an optical microscope, especially when no marking techniques are available. Furthermore, ferrofluidic liquid is often destructive to magnetic storage media.
Consequently, it would be desirable to provide an improved method and apparatus for indexing data storage media.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, a hard disk includes several essentially concentric magnetic tracks. A scanning probe is initially positioned at a first point located on a magnetic track to mark the first point as a first radial position index. Then, the scanning probe is positioned at a second point located on the magnetic track to mark the second point as a second radial position index. Next, the scanning probe is positioned at a third point located on the magnetic track to mark the third point as a third radial position index. A rotational center of a co-ordinate system is subsequently calculated according to the three radial position indexes. Finally, the coordinate system having the rotational center is utilized as a precise indexing system.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.
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Aurora Reena
Bracewell & Patterson L.L.P.
Lefkowitz Edward
Martin Robert B.
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