Dynamic magnetic information storage or retrieval – Head – Plural gaps
Reexamination Certificate
1999-12-30
2002-12-17
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Plural gaps
C360S122000, C360S125330
Reexamination Certificate
active
06496328
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to magnetic recording heads and more particularly to a structure for a ferrite driven, surface thin-film magnetic recording head wherein a substantial portion of the ferrite core has been replaced with a magnetically impermeable material and an optimal back-bar arrangement which reduces the inductance and increases the efficiency of the head.
BACKGROUND OF THE INVENTION
while variety of data storage mediums are available, magnetic tape remains a preferred forum for economically storing large amounts of data. In order to facilitate the efficient use of this media, magnetic tape will have a plurality of data tracks extending in a transducing direction of the tape. Once data is recorded onto the tape, one or more data read heads will read the data from those tracks as the tape advances, in the transducing direction, over the read head. It is generally not feasible to provide a separate read head for each data track, therefore, the read head(s) must move across the width of the tape (in a translating direction), and center themselves over individual data tracks. This translational movement must occur rapidly and accurately.
In order to facilitate the controlled movement of a read head across the width of the media, a servo control system is generally implemented. The servo control system consists of a dedicated servo track embedded in the magnetic media and a corresponding servo read head (which is usually one of the standard read heads, temporarily tasked to servo functions) which correlates the movement of the data read heads.
The servo track contains data, which when read by the servo read head is indicative of the relative position of the servo read head with respect to the magnetic media in a translating direction. In one type of traditional amplitude based servo arrangement, the servo track was divided in half. Data was recorded in each half track, at different frequencies. The servo read head was approximately as wide as the width of a single half track. Therefore, the servo read head could determine its relative position by moving in a translating direction across the two half tracks. The relative strength of a particular frequency of servo signal would indicate how much of the servo read head was located within that particular half track. The trend toward thinner and thinner magnetic tape layers causes amplitude modulation problems with this and other amplitude based heads. That is, as the thickness of the magnetic layer decreases, normal variations on the surface represent a much larger percentage variation in the magnetic layer, which will dramatically affect the output signal.
Recently, a new type of servo control system was created which allows for a more reliable positional determination by reducing the amplitude based servo signal error traditionally generated by debris accumulation, media thickness non-uniformity and head wear. U.S. Pat. No. 5,689,384, issued to Albrecht et al. on Nov. 19, 1997, introduces the concept of a timing based servo pattern on a magnetic recording head.
In a timing based servo pattern, magnetic marks (transitions) are recorded in pairs within the-servo track. Each mark of the pair will be angularly offset from the other. For example, a diamond pattern has been suggested and employed with great success. The diamond will extend across the servo track in the translating direction. As the tape advances, the servo read head will detect a signal or pulse generated by the first edge of the first mark. Then, as the head passes over the second edge of the first mark, a signal of opposite polarity will be generated. Now, as the tape progresses no signal is generated until the first edge of the second mark is reached. Once again, as the head passes the second edge of the second mark, a pulse of opposite polarity will be generated. This pattern is repeated indefinitely along the length of the servo track. Therefore, after the head has passed the second edge of the second mark, it will eventually arrive at another pair of marks. At this point, the time it took to move from the first mark to the second mark is recorded. Additionally, the time it took to move from the first mark (of the first pair) to the first mark of the second pair is similarly recorded.
By comparing these two time components, a ratio is determined. This ratio will be indicative of the position of the read head within the servo track, in the translating direction. As the read head moves in the translating direction, this ratio will vary continuously because of the angular offset of the marks. It should be noted that the servo read head is relatively small compared to the width of the servo track. Ideally, the servo head will-also be smaller than one half the width of a written data track. Because position is determined by analyzing a ratio of two time/distance measurements, taken relatively close together, the system is able to provide accurate positional data, independent of the speed (or variance in speed) of the media.
Of course, once the position of the servo read head is accurately determined, the position of the various data read heads can be controlled and adjusted with a similar degree of accuracy on the same substrate. Namely, the various read heads are fabricated on the same substrate with a known spacing between them. Hence knowing the location of one allows for a determination of the location of the remainder of the read heads.
When producing magnetic tape (or any other magnetic media) the servo track is generally written by the manufacturer. This results in a more consistent and continuous servo track, over time. To write the timing based servo track described above, a magnetic recording head bearing the particular angular pattern as its gap structure, must be utilized. As it is advantageous to minimize the amount of tape that is dedicated to servo tracks, to allow for increased data storage, and it is necessary to write a very accurate pattern, a very small and very precise servo recording head element must be fabricated.
Two types of servo recording heads having a timing based pattern are known. The first is a pure thin film head, such as that disclosed by Aboaf et al. in U.S. Pat. No. 5,572,392, issued on Nov. 5, 1996. With a pure thin film head, all of the components of the head are created from layering different materials, as thin films, on an inert substrate. For example, the magnetic core, the windings and any barrier materials are formed by producing thin films. Such a head has very low inductance, however, it is extremely difficult to manufacture. To date, pure thin film heads are generally not utilized for time based servo heads and are not seen as a practical way to produce such a magnetic head.
A very different type of recording head is taught by Albrecht et al. in the '384 patent. This second type of head is referred to herein as a surface film or surface thin film head and is illustrated as
100
, in FIG.
18
. The surface film head
100
includes two C-shaped ferrite blocks
110
,
112
that are bonded to a ceramic member
114
that extends the entire width of the head
100
. A surface is then polished flat or contoured and prepared for this film deposition. A magnetically permeable thin film
116
is deposited over an upper surface of the ferrite blocks
110
,
112
and the exposed upper portion of the ceramic member
114
. The thin film I
16
is shown much larger than it would actually be, respective to the other elements. Gaps
118
are formed in the thin film
116
, in an appropriate timing based pattern. Windings
120
are wrapped and are electrically driven to drive flux around the ferrite core and through the thin film
116
(in the direction of arrow A). The flux leaks from the gaps
118
and writes media passing over it.
Such a surface film head has a high inductance due to the large volume of ferrite forming the core and a high reluctance “back-gap”, due to the separation of the ferrite block
110
,
112
by the ceramic member
114
, on the underside of the head (i.e., opposite the th
Advanced Research Corporation
Dorsey & Whitney LLP
Klimowicz William
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