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BACKGROUND OF THE INVENTION
The present invention relates to an improved magnetic medium particularly
adapted for use with rotating head magnetic recorders, also referred to as
"transverse" magnetic recorders.
Rotating head recorders have been used for the last several years for
recording video or television signals. Such signals are analog in
character which permits repeated signal usage to compensate for defective
recording, while not materially detracting from the quality of the
television picture presented on a television set or CRT screen.
Such video recorders employ carrier recording techniques with the carrier
at the upper portion of the frequency band of the signals being recorded.
Such video recorders have been employed for digital data recording by
modulating digital data signals on the normal video carrier. In
contradistinction, most other digital data recorders employ baseband
recording rather than heterodyne the information-bearing signals on a
carrier.
Another aspect of digital data signal recording is that any error
conditions cannot be obviated in the same manner as video recording
signals can submerge or enable errors to be ignored. In data recording,
all signals read back from a record medium must be correct. Further, tape
motions employed with digital signal recorders and that of video recorders
are quite different. Requirements of a digital signal record medium
usually require that the magnetic recorder should be able to step the
medium to any selected position along its longitudinal length and then
precisely indicate to controlling apparatus that the medium is at the
desired location. In one form of digital signal data recorders employing
rotating heads, during the recording, the magnetic medium is completely
stopped; i.e., the apparatus operates on a step-by-step or incremental
mode. That is, one record stripe is recorded while the tape is stopped.
The tape moves to the next stripe with additional data being recorded,
etc. Accordingly, any article to be employed with digital data recorders
should be capable of being operated efficiently in a step-by-step or
incremental mode, as well as in a continuous motion or slewing mode.
The history of digital data recording on magnetic tape media indicates that
as the technology advances there is a great desire on the part of users
that there be backward compatibility. The term "backward compatibility"
means that all newly designed digital data recorders have a capability of
reading all previous digital data formats. For example, in the 1/2 inch
tape area, digital data recorders employing 1,600 cpi phaseencoded
recording also usually have the capability of reading the prior 800, 556,
and 200 cpi NRZI recording. Accordingly, any improved article for use with
rotating head digital data recorders should facilitate this so-called
backward compatibility.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved article for
a digital data bearing signal, particularly a magnetic article for
recording such signals.
In accordance with the invention, an elongated magnetically coated member
has a pair of spaced-apart, longitudinally extending, servo areas adapted
to receive digital data signals laterally extending therebetween. One of
the servo areas is spaced from one longitudinal edge of the tape for
receiving identification or address signals relatable to the data signals
recorded between the servo areas. Further, the servo areas extend
longitudinally to an extent demarking beginning of tape toward the leader
end of the article and end of tape, which denotes the spool end of the
article.
Further, at the BOT end of the article, a space between the servo areas is
reserved for density and format indicating signals for facilitating
backward compatibility of recorders employing the improved article. One of
the first data stripes adjacent the BOT end of the article includes the
serial number of the article. Such serial number is also printed at the
free end of the leader extending from the BOT area. A magnetically coated
portion is reserved for recorder calibration; that is, whenever the
article is loaded onto a rotating head magnetic recording apparatus, that
apparatus will record signals in the test area and read such recorded
signals back for calibrating the recording apparatus to the readback
signals.
In a preferred constructed embodiment of the invention, the data stripe
angle with respect to the longitudinal edge is about 171/2.degree.. The
distance between two gaps of a magnetic head on a rotor adapted to be
employed with the present article has an intergap distance slightly
greater than the 171/2.degree. angled width of the servo areas. It is
preferred that such recorder will employ the leading gap as a recording
gap, but switch such gap between readback and recording circuits such that
the recording gap can sense the servo track area signals simultaneous to
the read gap, reading the identification signals adjacent the one
longitudinal edge of the article. This action facilitates switching and
stepping of the article. As the write gap leaves the tape immediately
adjacent one of the servo signal areas, the read gap is still reading the
data area; then, the tape can be simultaneously advanced to the next
stripe. A preferred arrangement is such that the periodicity of the rotor
and the transit time between two adjacent data signal receiving stripes
permits the write gap and the read gap to simultaneously read such one
servo track area and said identification signals during that portion of
the latency period required to step the article.
In accordance with another aspect of the invention, the gaps are switched
in accordance with tachometer settings of the magnetic recorder for
switching the write gap between recording and readback operations.
The foregoing and other objects, features, and advantages of the invention
will become apparent from the following more particular description of the
preferred embodiment, as illustrated in the accompanying drawing.
THE DRAWING
FIG. 1 is a diagrammatic showing of an improved article constructed in
accordance with the present invention.
FIG. 2 is a diagrammatic showing of a pair of data signal receiving
stripes, together with the servo signal areas and identification areas.
Relationship of the geometry to intergap distance of a rotor is
illustrated.
FIG. 3 is a greatly enlarged diagrammatic showing of the relationship of
the servo track area, identification area, and a signal envelope derived
from the improved article by a rotating magnetic transducer.
FIG. 4 is a diagrammatic showing of a rotating head recording apparatus
adapted to utilize the present inventive article.
DETAILED DESCRIPTION
Referring to the drawing, like numerals indicate like parts and structural
features in the various views and diagrams. The improved article of the
present invention is advantageously mounted on a single flange spool 10. A
cylindrical sleeve (not shown) fits on the spool to complete a dust-proof
enclosure for the record article. The improved article includes elongated
member 11 having a magnetic coating on one face thereof. The free end of
member 11 is tapered at 12 for facilitating automatic threading. In the
free-end portion, as at 13, a plurality of imprinted article serial
numbers reside on the coated side of the article. The imprinted serial
numbers are viewable through a covering transparent cylindrical sleeve
(not shown). Such printing enables visual inspection and identification of
various improved articles for facilitating handling and transfer. Such
serial numbers facilitate logging performance statistics about each of the
articles, as well as facilitating identification.
Immediately adjacent free end 12 is a leader area 14 which may or may not
have magnetic coating thereon. Leader 14 facilitates automatic threading
operations. Immediately adjacent area 14 is a magnetically coated test
area 15 for enabling recording and readback of signals by each digital
signal recorder employing the improved article. A test pattern of signals
recorded in area 15 is sensed by the digital signal recorder. The
amplitude, phase shift, and other characteristics of the readback signal
are analyzed by recorder circuits which then automatically adjust the
readback circuits for optimum readback of data signals recorded on the
improved article. The details of such automatic readback circuits are not
a part of the present invention.
The data recording area 16 of the improved article is completely defined
and located by a pair of servo track areas 17 and 19. Each servo track
area in a constructed embodiment of the improved article included areas
for two parallel longitudinally extending servo tracks. The servo tracks
contain signals identifying data stripe locations indicated by dashed
lines 20 in FIG. 1 and by long narrow rectangles 21 and 22 in FIG. 2.
Each of the servo tracks in areas 17 and 19 may be constructed in
accordance with U.S. Pat. No. 3,691,543, no limitation thereto intended.
In the alternative, a single servo track may be employed in each of the
areas 17 and 19.
The servo track areas 17 and 19 have precise longitudinal extents and
locations. These areas demark all recording areas on the tape. The servo
area ends adjacent free end 12 define beginning of tape, labeled "BOT,"
which signifies the area in which a rotating head can start recording data
signals. In a similar manner, the spool ends of servo track areas 17 and
19 precisely denote end of the tape, labeled "EOT," which correspondingly
defines the other longitudinal limit in which a recorder may record data
signals.
In addition to data signal receiving area 16, which is left blank when the
improved article is first manufactured, an identification and addressing
track is located at 25 with a longitudinal extent substantially
longitudinally coextensive with servo area 19. Identification and
addressing area 25 will be described in detail later. In an early
constructed embodiment of the present improved article, the identification
area ended at 26 longitudinally toward spool 10 from free end 12. The
first data record area number was 0 identifying a so-called "stripe 0." In
this first constructed embodiment, stripe 0 had recorded therein the
serial number of the improved article, which serial number corresponded
with the printed serial numbers at 13.
In practice, a digital signal recorder would receive the improved article
and read stripe 0 to identify the particular article. In a preferred form
of using the improved article, apparatus employing the article would
identify which articles had never been used, i.e., "scratch" articles, and
other articles which had previously received recording. For such scratch
articles, stripe 0 is initially read, the article moved to stripe 1, with
the serial number then recorded in stripe 1. Subsequent loading of such
article into a digital signal recorder apparatus causes the apparatus to
move to stripe 1 for reading the serial number. In this manner, possible
erasure or other destruction of the serial numbers in stripe 0 is
minimized. One procedure for effecting such protective reading is to
always have the digital recorder step to stripe 1. If the stripe is
erased, then stripe 0 is read. If the stripe 1 is in error, then
additional stripes 2-9 may be employed for receiving such serial number.
Additionally, other data may be recorded in stripes 1-9, such as usage
indicators, error status, and other information usually found in header
labels of one-half inch magnetic tape record media.
The longitudinal space extending from point 26 to BOT and disposed
intermediate servo areas 17 and 19 is reserved for density and code
indicating information. Such an area may accommodate up to 100 stripes,
for example. When the first type of recording is employed, then all of
such stripes in areas 26 to BOT are left blank. For a first modification,
such as increased density, variation of stripe width, spacing, etc., a
first particular code is inserted in the density area between space 26 and
BOT, identifying the newer recording format. By such identification,
backward compatibility of the recorded improved article is identifiable.
In accordance with all of the above, the improved article, when shipped
from a manufacturing plant, includes servo stripe areas 17 and 19 with
their associated servo stripes, identification and addressing area 25, and
the printed serial numbers at 13. Area 25 can have addresses 00000 to
13342 (decimal). The address signals consist of two 8-bit binary coded
bytes which may be subjected to error correction codes or be redundantly
recorded, as one pleases. All recording is inset from longitudinal edges
30 and 33 to provide a guard area of no recording.
Referring now more particularly to FIG. 2, the relationship of the improved
article to a particular digital signal recorder with which the improved
article can be advantageously employed is described. The timing
relationship of the rotating head scanning of the tape with respect to the
servo track areas and the identification and address stripe show the
advantageous usage. As mentioned above, in a first constructed embodiment
of the improved article, the angle of the data stripes, such as stripes 21
and 22, with respect to the longitudinal edges of the tape, is about
171/2.degree.. The data receiving areas 21 and 22 extend at such an angle
between the precisely aligned servo areas 17 and 19. The lateral extent of
the servo areas 17 and 19, as measured along the scan path 27 of a
rotating head, is slightly less than the intergap distance between a write
(W) and a read (R) gap of the single two-gap head on the rotor, as will be
later described. This intergap distance, as at 28, being slightly greater
than such transverse dimension of the servo areas, is advantageously
employed when recording and stepping the improved article by a digital
signal recorder. Assume that when gap W is scanning the tape at the lower
edge 30, it is connected to a readback circuit. Gap W scans the address
portion 25. The readback signals being identified as data signals are
ignored. As gap W scans servo area 19, the readback signals are identified
as servo signals and sent to a servomechanism used in connection with
transporting article 11 past the rotating heads having gaps W and R. As
gap W scans area 19, at 171/2.degree., trailing gap R follows by distance
28 to simultaneously scan address area 25. The servo signals from gap W
drive the servomechanism simultaneous with other readback circuits,
analyzing the signals from area 25 to identify the location of the
improved article with respect to gap W. After gap R has completed a scan
of the appropriate portion of address area 25 signals, electronic circuits
determine whether or not the article is appropriately positioned. If it
is, then recording currents are turned on for recording data signals in
stripe area 21, precisely aligned along the 171/2.degree. scan path with
the appropriate portion of servo tracks in area 19, as well as the
later-described address portion of area 25 associated with data signal
receiving area 21. As gaps W and R continue to scan across tape 11, the
signals are recorded through gap W into data signal receiving area 21. For
checking the correctness of the recording in area 21, the recorded signals
are simultaneously sensed by gap R as it scans area 21. Such
read-after-write recording verification can follow the same procedures
used in connection with prior digital data signal recorders, such as
employed for 1/2 inch tapes.
As gap W leaves area 21, as at 31, all recording currents are removed from
the gap. Gap R continues to sense the recorded signals. Gap W senses the
area 17 servo signals to supply servo track signals to said servomechanism
for use in connection with positioning the article, as is well known.
Since the intergap distance 28 is slightly longer than the 171/2.degree.
transverse dimension of area 17, gap W leaves area 17, as at 32, about
substantially coincidentally with gap R leaving area 21, as at 31. At this
time, gap R is substantially transversely inward of upper edge 33 of tape
11. The servomechanism is now actuated to step the article 11 to the next
stripe, such as stripe 22. The constants of acceleration and the rotor
velocity can be matched such that the stepping to stripe or signal
receiving area 22 is the same time it takes for gap W to move from area 17
to just immediately prior to area 19 which is aligned with stripe 22. This
transit time corresponds to the transverse dimension from area 17 to edge
33, plus the distance from edge 30 to lower edge 34 of area 19. This
statement assumes a helical wrap of 360.degree. of article 11 around a
laterdescribed mandrel, such that edges 30 and 33 abut. In this manner,
for a single head type rotor, a minimum time is lost because of the rotor
movement and tape movement for maximizing data signal throughput.
Referring next to FIG. 3, the detailed relationship of the address area 25
with respect to the data receiving area 16 is further explained. The
address area 25 is recorded on the improved article in accordance with the
Harr U.S. Pat. No. 3,366,897. Area 25 includes one address signal
receiving area 40 corresponding to each data signal stripe or receiving
area, such as areas 21 and 22 of FIG. 2. Areas 40 are precisely aligned
along the 171/2.degree. scan path, with corresponding servo information
signals in the servo areas 17 and 19. For example, assume that stripe J is
to be accessed. It has an address area JID in area 25, which identifies
the longitudinal address of stripe J. Read and write gaps R and W scan the
hatched area 42 of address portion JID. The gap center line 43 identifies
the scan path of both gaps. Stripe J, after recording by a suitable
positioning based upon the servo tracks in area 19, corresponding to servo
positioning indicating signals as at 44 and 45, is precisely aligned with
JID center portion. In a similar manner, servo track area 17 has an
additional pair of servo positioning signals corresponding to stripe J.
The signal envelope appearing from gap R in reading JID and stripe J is
shown in the lower part of FIG. 3. Signal envelope portion A corresponds
to gap R reading portion A of JID+1; i.e., only a portion of the gap R
senses JID+1. The space between A and the signal JID' is the interaddress
gap, as at 50. The JID' signal represents a full scan of the address area
JID, enabling signal detection in accordance with known techniques.
Following the JID' signal, gap 51 appears, followed by signal B from gap R
sensing the B portion of address area JID-1. Then, the servo tracks are
sensed (envelope now shown); following that, the data stripe J is sensed,
as indicated by the signal J' followed by sensing the servo tracks from
area 17, the signal envelope which is not shown.
It should be noted that the addressing and the data signals are read by gap
R, while both servo tracks are read by gap W. Additionally, gap W records
signals in the data stripe area, as well as selectively recording signals
on the address portion, as will be later described. The preferred write
gap to read gap ratio is about 2:1; i.e., the write gap scans a wider
track than the read gap as commonly practiced in one-half inch tape
recorders.
Referring next to FIG. 4, using the improved article in a rotating head
digital signal recording apparatus is further described. The improved
article 11 has a helical wrap around an air bearing mandrel consisting of
two halves 60 and 61, the mandrel being stationary. Precisely coaxially
aligned with the cylindrical mandrel 60, 61 is a single axially thin rotor
62 which carries gaps W and R, as above referred to. The intergap distance
is the short distance between the gaps. A rotary transformer (not shown)
of usual design is included in rotor 62 to provide electrical connections
over lines 63 and 64, respectively, between gaps W and R and electronic
circuits diagrammatically shown in FIG. 4.
Rotor 62 is driven at a constant angular velocity by motor 70. Motor 70
also includes a precisely constructed tachometer disk 71. Disk 71 has
fiducial mark 72 precisely aligned with the angular position of gaps R and
W such that sensor 73, supplying a signal indicative of sensing fiducial
mark 72, provides a precise relationship of the angular location of gaps W
and R for use in connection with the medium format shown in FIGS. 1 and 2.
Sensor 73 supplies its fiducial signal to reset angular position counter
74 to a reference state, such as all 0's. In addition, sensor 75 senses
the positional marks evenly distributed around the circumference of disk
71. Sensor 75 supplies corresponding angular position-indicating signals
to counter 74 to tally same for indicating the present angular position of
gaps R and W. For example, if the counter is set to all 1's by the reset,
then the tally signals from sensor 75 decrement the counter toward zero as
motor 70 rotates rotor 62 and tachometer disk 71. In the alternative, when
counter 74 is set to all 0's, the tally signals from sensor 75 may
increment the counter. Other reference states may be used in the counter
in accordance with machine design principles.
The present count in counter 74, i.e., the indication of the angular
position of gaps R and W, passes head-switching positions represented by
signals on the lines 80, 81, and 82. These positions correspond to the
read and write gap positions, as shown in FIG. 2.
Since the apparatus is employed for recording digital data signals, a
computer (not shown) is usually connected to the apparatus, no limitation
thereto intended. The computer supplies the usual control signals for
digital signal recorders and, in addition, supplies digital signals to be
recorded. Recording circuits 84 receive the computer-supplied signals and
convert them to a form suitable for recording on article 11. Such a form
may be NRZI digital signals, as taught by Phelps in U.S. Pat. No.
2,774,646. Such NRZI recording, as taught by Phelps, is preferably encoded
for reducing the charge effects in the rotary transformer. To this end,
the record code taught by Patel in commonly assigned co-pending Pat.
application Ser. No. 369,675, filed June 13, 1973, may be advantageously
employed for recording signals in the data signal receiving area 16, as
well as certain signals to be recorded in the address area 25. Such
recording includes a preamble clock synchronizing set of signals, such as
those employed in phaseencoded recording.
Signals to be recorded are supplied by recording circuits 84 through AND or
coincidence circuit 85 for being supplied over line 63 to gap W. AND 85
passes such signals only when the gap W is scanning that portion of
article 11 corresponding to the digital data signal receiving stripes in
area 16. Counter 74 is constructed to decode the counts for defining data
signal receiving area 16 by supplying a relatively low amplitude signal
over line 80; i.e., the signal on 80 represents a series of tachometer
counts from disk 71 corresponding to the scan portion represented by
stripes 21, 22, etc. The signal on line 80 is supplied through inverting
amplifier 86 to AND 85 for enabling the recording of signals by gap W. At
all other times, coincidence circuit 85 is disabled, thereby protecting
the integrity of the signals recorded at a manufacturing plant in servo
areas 17 and 19 in accordance with the Harr patent, supra.
Gap W scans the servo areas 17 and 19, which have a predetermined
relationship with the above-mentioned data receiving area, such that a
second predetermined set of counts from disk 71, as manifested in counter
74, can be used to open AND circuit 87 to pass signals from line 63 to
servo circuits 90. In this regard, whenever address area 25 is not to be
updated, the signal on line 80 is passed through OR circuit 91 to enable
AND 87 whenever AND 85 is disabled. Hence, in this manner, the signals on
line 63 are passed to servo circuits 90 whenever the gap W is scanning a
portion of the tape outside the data signal receiving area. Servo circuits
90 are constructed to ignore the data signal type of readback signals.
In addition, gap R supplies signals over line 64 to a set of readback
circuits 95. Readback circuits 95 supply such readback signals to the
computer whenever gap R is scanning signals in the data signal receiving
area 16. This is indicated by the output of inverter 86. At other times,
gap R is scanning area 25, which is indicated by the signal on line 81. In
a similar manner, the signal on line 82 indicates gap R is scanning a
nondata area of the tape. Similarly, the signal on line 82 disables
readback circuits 95 whenever gap R is not scanning a signal receiving
area on tape 11.
As additional controls and variations of modification of the signals are
recorded on improved article 11, electronic circuits associated with a
given digital signal recorder must necessarily become more complicated. In
the preferred form of the invention, address area 25 has a set of
addresses beginning at zero adjacent BOT extending through a predetermined
number of stripes at EOT, for example, 13,342, with the stripes being
spaced center-to-center of about ten mils with a width of 6 mils, leaving
an interaddress space of 4 mils. The data signal receiving stripes 21 and
22 can be made contiguous provided the recording signal apparatus has
sufficiently accurate servo circuits and guiding apparatus (not shown) for
precisely aligning each of the stripes as diagrammatically illustrated in
FIGS. 1 and 2.
Since recording in data signal area 16 is initiated only after the article
has been accurately positioned and such positioning verified, all data
stripes 00000 to 13,342 are precisely aligned with the corresponding
portions of the servo track areas 17, 19 and address signals at 25.
Positioning control 100 coordinates medium 11 transport with rotor 62
position in a known manner. Supply or payout reel 101 driven by motor 102
and capstan-reel or takeup reel 103 via motor 104 are also coordinated in
operation in accordance with Phillips U.S. Pat. No. 3,781,490. Tachometer
105 supplies position data signals to control 100. Translation of capstan
reel 103 rotation to actual linear tape motion is calculated by the
computer in accordance with tape wrap radius on capstan-reel 103.
Threading medium 11 from reel 101 to reel 103 is in accordance with
established automatic threading techniques.
It is anticipated that the illustrated record medium may be used by several
different tape units as diagrammatically shown in FIG. 4. Such tape units
usually will have different tape-guiding characteristics yielding slightly
different record stripe angles --such angle differences are termed "skew."
Such skew can result in readback errors, unintended recording overwriting
resulting in obliteration of previous records. In spite of this skew
problem, it is commercially imperative that record stripes be changeable
without unintentionally obliterating any recorded signals. For achieving
such a re-recording capability without error, record stripes 20 are
grouped into record blocks such as 110 and 111, each such record block
being separated by an area 112 containing no recorded signals. To
re-record, one entire block 110 or 111 is recorded at a time. Following
such a practice accommodates tape-guiding tolerances of various tape
units.
Each record block may contain any number of record stripes 20; it is
preferred that a fixed number of record stripes be selected, such as 50,
100, etc. Such a selection simplifies programming in computers using the
illustrated record medium for data signal storage.
For maximizing data signal storage on each medium, area 112 (termed
interblock gap or IBG) has a minimal length, for example, a length
sufficient to accommodate one or two record stripes. Identification
portion 25 can contain special indicia (all 1's, etc.) signifying an IBG,
the computer recognizes IBG's by specified addresses, or the IBG can
extend into portion 25.
It is preferred, for maximum flexibility, that each block and IBG be
identified by decimal address such as set forth below for a 65-stripe
block:
Block Number
Block Addresses IBG Addresses
______________________________________
0 0-64 65
1 66-130 131
2 132-196 197
3 198-262 263
4 264-328 329
5 330-394 395
. . .
. . .
. . .
N 66N - (66.N+64) 66N + 65
______________________________________
Each address consists of two bytes (address modulus of 2.sup.16 -1)
recorded in the ID portion 25 in accordance with the Patel et al.
co-pending application, supra, and Harr U.S. Pat. No. 3,666,897. The
recorded signals appear in seriatim at the 171/2.degree. angle.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood by
those skilled in the art that various changes in form and detail may be
made therein without departing from the spirit and scope of the invent | | |
