Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-06-28
2004-04-20
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S076000, C360S077020, C369S044370
Reexamination Certificate
active
06724561
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed to an apparatus and method for compensating for environmental effects on media. In particular, the present invention is directed to an apparatus and method for compensating for the effects of tape creep in magnetic tape media.
2. Description of Related Art
Magnetic tape recording has been utilized for many years to record voice and data information. For information storage and retrieval, magnetic tape has proven especially reliable, cost efficient and easy to use. In an effort to make magnetic tape even more useful and cost effective, there have been attempts to store more information per given width and length of tape. This has generally been accomplished by including more data tracks on a given width of tape. While allowing more data to be stored, this increase in the number of data tracks results in those tracks being more densely packed onto the tape. As the data tracks are more closely spaced, precise positioning of the tape with respect to the tape head becomes more critical as errors may be more easily introduced into the reading or writing of data. The tape head positioning may be affected by variations in the tape or tape head, tape movement caused by air flow, temperature, humidity, tape shrinkage, and other factors, especially at the outside edges of the tape.
In order to increase data track accuracy, servo tracks have been employed to provide a reference point to maintain correct positioning of the tape with respect to the tape head. One or more servo tracks may be used depending upon the number of data tracks which are placed upon the tape. The sensed signal from the servo track is fed to a control system which moves the head and keeps the servo signal at nominal magnitude. The nominal signal occurs when the servo read gap is located in a certain position relative to the servo track.
Referring to
FIG. 1
, a one-half inch wide length of magnetic tape
11
may contain up to 288 or more data tracks on multiple data stripes
12
. A thin film magnetic read head is shown in upper position
13
and lower position
14
to read data from data tracks
12
. If a tape read head has sixteen elements and, with movement of the head to multiple positions, each element can read nine tracks, then that magnetic read head could read 144 tracks. In order to read more tracks, such as 288 in the desired configuration, two data bands
15
and
16
are utilized. The tape head is movable to nine tracking positions in each of upper position
13
and lower position
14
. That is, with the tape head in position
13
it can read 144 tracks in data band
15
and in position
14
it can read 144 tracks in data band
16
. With dual data bands
15
and
16
and multiple head positions within those bands, tape head positioning is critical.
In order to achieve accurate multiple head positions it may be desirable to include up to five or more servo stripes
17
. Servo stripes
17
may utilize various patterns or frequency regions to allow precise tape to tape head positioning in multiple positions. This allows a data read head to more accurately read data from data stripes
12
. Referring to
FIG. 2
, servo stripes
17
are shown in greater detail. As is disclosed in copending U.S. Pat. No. 6,023,385, entitled TAPE SERVO PATTERN WITH ENHANCED SYNCHRONIZATION PROPERTIES issued on Feb. 8, 2000, and hereby incorporated by reference, a first frequency signal
19
is written across the width of a frame
18
in each servo stripe
17
. As is known in the art, a measurably different frequency signal such as an erase frequency is written over first frequency signal
19
in a predetermined pattern such as the checker board patterns in regions
21
and
22
. The horizontal sides of twelve rectangles
20
and
23
in each stripe
17
are substantially parallel to the direction of movement of tape length
11
. The six rectangles (12 sides) in each region
21
and
22
define five horizontal interfaces (servo tracks)
24
between frequency signal
19
. Rectangles
20
and
23
as the outside interfaces
25
along the top and bottom of each stripe
17
are ignored. In the preferred embodiment rectangles
20
are shown on the left side of areas
21
and
22
and rectangles
23
are shown on the right portion of areas
21
and
22
. A servo read element
26
in a tape read head is precisely aligned along interface
24
to read the signal frequency along interfaces
24
. That is, dotted line representing interface
24
along the horizontal sides of rectangles
20
.
23
passes through the center of servo read element
26
. If the servo pattern on the tape moves right to left, then servo read element
26
will alternate between reading frequency
19
across the full width of servo read element
26
and an erase frequency from rectangles
20
.
23
across the other half of the width of servo read element
26
. Thus, if tape
11
moves as shown in
FIG. 2
, servo read element
26
will first sense rectangle
20
above track
24
and then sense rectangle
23
below track
24
in each of regions
21
and
22
.
As is known in the art, the servo control system in a tape drive determines the position error signal (PES) by using the ratio of the difference between the signal amplitude sensed during the first (left) half of patterns
21
or
22
and the signal amplitude sensed during the second (right) half of patterns
21
or
22
divided by the sum of the signal amplitude sensed during the first half of patterns
21
or
22
and the signal amplitude sensed during the second half of patterns
21
or
22
to stay on track. For a head position precisely on track in checkerboard pattern areas
21
or
22
shown in
FIG. 2
the ratio will be zero because the signal amplitude during each half of the pattern will be the same. If servo read element
26
is above track
24
, the position error signal will be non-zero because less of the erasure area is read and thus, the amplitude of the signal is not reduced to zero. In response, the track servo will move the head (including servo read element
26
) down until the ratio is zero and servo read element
26
is precisely on track
24
. Conversely, if servo read element
26
is below track
24
, the polarity of the position error signal will be negative because more of rectangle
23
below track
24
and less of rectangle
20
above track
24
will be read. In response, the track servo will move the head (including servo read element
26
) up until the ratio is zero and servo read element
26
is precisely on track
24
. In this way the tape controller can determine the position of the tape
11
with respect to the servo read element
26
and move the tape head to keep the head servo read element
26
aligned with the servo track along line
24
. This alignment ensures precise reading of a data track in data stripes
12
by the data read head (not shown).
Over the life of a magnetic media, such as magnetic tape, the configuration of the magnetic media may become warped or otherwise changed from the original configuration of the magnetic media. For example, due to stresses applied to a magnetic tape, the tape width may begin to migrate, i.e. the tape may become bowed-in at the edges or bowed-outward. This phenomenon is known as tape creep. Because of tape creep, the servo reader elements of a read head may not be properly positioned relative to the servo tracks on the magnetic media. Hence, the data reader elements will not be properly positioned relative to the data tracks on the magnetic media. This may lead to errors in reading information from the data tracks.
Furthermore, the position of conventional servo reader elements may not be able to be adapted to compensate for the tape creep phenomenon. This is because known read head adjustment methods only reposition the position of the read head in a perpendicular direction to the magnetic tape, i.e. with reference to
FIG. 1
, in a vertical direction relative to the magnetic tape. These known adjustment methods are directed to compensating for a shift of t
Bailey Wayne P.
Carstens Yee & Cahoon LLP
Sniezek Andrew L.
Storage Technology Corporation
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