Note: Descriptions are shown in the official language in which they were submitted.
lOSf~498
1 ~CKGROUND OF T~ INVENTION
The present invention relates to a recording
method and apparatus for accurately inserting new records
in specific previously recorded segments at any given point
along a length of recording tape.
; In certain prior recording formats for digital
;~ recorded tape cassette systems, each record was preceded
by a start-of-record mark consisting of a single recorded
transition followed by a 36-bit gap, after which the record
commenced. The start-of-record mark was read and employed
as a synchronization signal to facilitate the insertion
a predetermined timed interval after such maTk was read,
; of new record information over the old record, to effect
re-recording of that part of the tape. The ixed 36-bit
gap allowed suficient time for the start-of-record mark
to be moved past the recording head and detected by the
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latter and then a predetermined interval later, the recorder
apparatus could be switched to the write mode of operation
to apply new recording information to the tape, over the
old record.
Recently, the European Computer Manufacturers
-~ Association (E.C.M.A.), the International Standards
Organization ~I.S.O.) and the American National Standards
Institute (A.N.S.I.) have adopted universally acceptable
standards for data interchange using 3.81 mm magnetic tape
:,
; cassettes. The standards include a new format which
eliminates the use of the previous start-of-record mark
followed by a gap between the mark and the recorded data.
The new standards thereby prevent the use of the previous
system for recording new record information on a previously
recorded tape in an accuraSe fashion. In the new format,
1(1 5~i498
1 a universal preamble is followed immediately by the
data, with no gap between the two~ This makes it im-
possible to insert a new record in the same manner as
before, or in a somewhat analogous manner~ such as or on
timed response to the passing of the preamble past the
recording head or past a typical read-after-write head
(OT gap, in a double-gap head) used for data verification
and error checking, since in either case the head or gap
which does the writing will be well into the data information
by the time the preamble has moved past the head or gap
; used for reading, and has been so identified.
SUMMARY OF THE INVENTION
In order to accurately insert new records,
therefore, a new system has been developed which utilizes
the write head for detecti~g the first transition of the
preamble and applying the detected signal to a threshold
; detector. As a predetermined signal level is reached,
the tape apparatus is controlled to immediately record a
new preamble which is immediately followed by the new
record. In the new re~ord-inserting method, therefore,
the preamble as well as the old record is replaced with a
new preamble and record.
It is an object, therefore, of the present inven-
tion to provide a recording method suitable for inserting
new records in place of old records, following a re-
cording format utiliæing a preamble immediately preceding
the recorded data.
Another object of the present invention is to
provide a method of, and apparatus for, inserting new
records accurately over old records by employing the
writing head to detect the start of the old record.
105f~98
l Another object of the present invention is to
provide an improved record-inserting method and apparatus
which utilizes the write head and a threshold detector to
provide a control signal upon the detection of a pre-
determined level of the first transition of a record and
provide a control signal therefrom utilized to initiate
the re-recording of the record.
Still a further object of the present inven-
tion is to provide an electrical circuit coupled to the
writing head of a data recording apparatus and responsive
to the leading transition of a record to accurately insert
new information in place of the previously recorded in-
formation.
These and other objects of the present inven-
tion will become apparent upon reading the following
specification together with the accompanying drawings in
which:
BRIBF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an elec~rical circuit diagram par-
tially in block and schematic form illustrating the method
and circuitry employed in practicing the present invention;
`~ Fig. 2 is a pictorial diagram of an enlarged
segment of magnetic tape prerecorded in the recently
adopted standardized format;
Fig. 3A is a diagrammatic view of a segment of
the tape shown in Fig. 2; and
Fig. 3B is a diagrammatic view illustra~ing
the electrical signal developed from the write head shown
in Fig. 1 in response to the tape segment shown in Fig. 3A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Before discussing the circuitry of Fig. 1 in
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1056498
1 detail, it is helpful to examine the recor~ing format
recently adopted by E.C.M.A /I.S.O./A.N.S.I. The format
as shown on tape 20 in Fig. 2 includes an inter-record
gap 22 between individual records, i.e., discreet sequential
areas or segments of recorded information. The gaps range
between a minimum of 17.8 mm to 500mm. Immediately
following an inter-record gap is a recorded segment or
record comprising a preamble 24 which is the digital code
01010101 and which is followed immediately by the data
26 of the record itself (i~e., the information)~ The
record can range from 32 to 2,064 bits of information.
The data is followed by a postamble 28 comprising eight
bits which is then followed by another inter-record gap
22' preceding the preamble 24' for the next record.
lS The preamble is in every case identical and immediately
precedes the data record.
With this format, the read-after-write head
which can be a seperate and distinct head or merely a
separate magnetic gap in a dual gap head, which is of
- 20 necessity, located downstream from the writing head or
gap, cannot read the preamble sufficiently soon to control
the reinsertion of a new data record over the old
,
record. This results since there is no spacing between
the preamble and the data in the record, and by the time
~he preamble is read, the write head is positioned well
into the data. In order to insert records employing this
new format, therefore, it is necessary either to stop
and reverse the tape a predetermined distance with extreme
~; accuracy after detection of the preamble, or to employ
additional components, at additional expense and complexity,
such as for example, another read head located upstream from
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~056498
1 the write head.
The system shown in Fig. 1 represents a new
approach which can be employed with the recently adopted
recording format (and others) to successfully and accurately
re-record a tape cartridge by recording a new record
directly over the old record without reversing and restarting
the tape. Before discussing the operation of the system
shown in Fig. 1, a brief description of the circuit
elements contained therein is presented.
Referring now to Fig. 1, there is shown a tape
recording-playback apparatus 10 suitable for cassettes or
other types of tape sources, including a tape drive unit
or transport 12 adapted to move magnetic tape 20 past a
` write head 14 and then past a read head 16 or past write
and read gaps in a dual gap head, the read head or gap
beîng positioned in spaced relationship from the write head
or gap, downstream therefrom with respect to the direction
of motion of tape 20, indicated by arrow A in the figure.
Transport 12 can be any commercially available unit adapted
to utilize a conventional Philips cassette, transporting the
tape at approximately 12.5 inches per second during reading
and writing. The transport is mechanically coupled to the
tape 20 as by means of a capstan or other suitable drive
menas, represented schematically by the dashed line 15
ext~nding between the transport and the tape.
Apparatus 10 includes a tape controller 30
shown in dashed lines in the figure and which includes the
circuitry for controlling the tape drive mechanism as well
as applying data to the write head 14 from a data source 32
~ 30 which can be any number of commercially used units such as
- a computer, prerecorded tape, or other data generating
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1056498
1 sources such as keyboards or the like. The controller also
is coupled to the read head 16 for transferring information
stored in tape 20 to a data utilization circuit 34 which, like
source 32, can be any number of commercial units including
another computer, numerically controlled machine tools
or process controls, inventory control systems or the like,
Controller 30 includes a logic and control ~-
circuit 36, which may be a conventional type of switching
: network design, to selectively couple the data signals
supplied thereto between the heads and the input and output
devices as well as control the different ]nodes of operation
of apparatus 10 upon command by appropriate switching
The particular circuitry required for this component is
easily within the state of the art and in large part can
be selected from existing circuits which are in use in
similar applications; for example several tape-controlling
,.
circuits of this general nature are presently in use in
commercial tape recorder devices, and could be employed with
:. very minor modification to provide the essentially standard
types of switching functions required.
Controller 30 additionally includes a read
amplifier 40 coupled to read head 16 for amplifying detected
recorded information and applying the information to a wave
shaping circuit 42 which converts the generally sinusoidal
signals 41 into square wave data signals 43 as seen in
Fig. 1. Data signals 43 are then applied to the logic and
. control circuit 36 which feeds them to the data utiliza-
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.~ tion circuit 34 via interconnecting conductor(s) 33.
~:,
:. It is to be noted here that the present inven-
tion recognizes and makes use of the fact that the write s
head or gap 14, although specifically designed and typically
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~05~498
l used only to apply magnetizing fields to record the tape
20 as it passes thereby, can nonetheless be utilized as a
reading head to detect prerecorded information on the tape.
This typically un-noticed and unused capability is utilized
in a highly effective and novel manner in accordance with
the invention to solve the problem set forth above, i.e.,
the accurate insertion or re-recording of a new or changed
record directly over ~hat which was previously recorded.
That is, in accordance with the present invention, the
write head or gap is used to read the tape, to thereby
detect the presence at the write head of the preamble in
the record which is to be changed. To facilitate the
recovery of such information from the write head, a read
amplifier 50 has its input terminals coupled to the write
head 14 and amplifies signals detected by the write head
when not operated in a recording mode. The generally
sinusoidal signals 51 are applied to a threshold detector
circuit 52 which, as seen in Fig. 1, includes a comparator
54 and a reference voltage source 56. The output terminal
55 of a comparator 54 is coupled to the logic and control
circuit 36.
Controller 30 additionally includes a write
driver 60 having its output terminals 61, 61' coupled
:,
to the writing head for applying signals which actuate
the head to record data information supplied from source
32 on tape 20 as it passes the head. An AND gate
circuit 62 has first terminal 63 for receiving an
enabling signal from the logic and control circuit 36,
whereupon ~he gate will pass data to driver 60 from gate
input terminal 64, which is coupled to the data source 32
through appropriate gating or switching in the control
--8--
.
lOS~498
1 circuit 36. Thus, the driver 60 will be actuated to apply
data recording signals to the write head only when an
enable signal is applied to terminal 63 of the AND gate
from the logic and control circuit 36. During recording,
amplifier 50 may be ~isabled as by an appropriate control
signal from circuit 36, applied to the amplifier, for
example, on a conductor 37; however, it is to be noted that
such disabling is not strictly necessary, so long as the
control circuit 36 is not responsive to signals from the
comparator during recording operation If not disabled,
amplifier 50 will probably be situated, but this is not
necessarily harmful or damaging As will be understood,
circuit 36 should include a gate or other suitable logic
or switching circuitry which responds to a control detector
to provide the enabling signal applied to gate 62, as
well as a disabling signal applied to amplifier 50, if
disabling is deemed necessary. Recording is accomplished
by switching the controller to a recording mode of opera-
tion during recording of previously unrecorded tape or
is accomplished automatically when recording over previously
recorded tape in accordance with the present invention
as now described.
OPERATION
Referring now to Fig. 3A, there is shown a portion
of the tape 20 including the recorded preamble. Aligned
below the tape in relationship to the information recorded
on the tape is Fig. 3B, showing a wave form 70 illus-
trating the output voltage from the read amplifier 50
shown in Fig. l. As noted earlier, tape 20 includes the
inter-record gap 22, which separates sequentially re-
corded individual records. Information is recorded on the
.~ ~ g
105~45~8
l tape in phase encoded form such that data "l" signals are
sections of tape magnetized in a first direction illus-
trated by arrows B, while data "O" signals are sections
of tape magnetized in the opposite sense as indicated by
arrows C. The transition between the two differen~ mag-
netized sections provides the detected signal employed
to represent the recorded information. To re-record
over a previously recorded segment, the tape is cued to
the gap preceding the record to be changed as by means of
1~ automated i.e.~ programming search routines, or by means of
a counter associated with the tape apparatus, or other
suitable means, and control circuit 36 is actuated to the
re-recording mode, so as to be responsive to the amplifier
50 and the threshold detector circuit 52.
The tape drive is then started, and the part
of the tape carrying the record which is to be changed
approaches the write head, which is then in a reading mode
of operation selected by the operator when the desired record
is cued for reprogramming. As the first bit 25 of the
preamble 4 in the selected record approaches the write
head, the output voltage of amplifier 50 increases toward a
positive peak 72 as seen on wave form 70. It is to be
particularly noted that the voltage from amplifier 50
actually begins to rise before the first bit in the preamble
becomes directly aligned with the gap of the write head,
as a result of ~he tape magnetization characteristics.
This appears to have been unappreciated heretofore, at
least in so far as the use of such characteristics for
; anticipatory detection of recorded bits, as is true in
accordance with this invention. That is, the magnetization
characteristics of the tape are changed in varying amounts
-10-
1~5~4g8
1 in the area surrounding the actual recorded transition, as
well as at the transition itself, where magnetization is
very direct and strong. The area of changed magnetization
surrounding the actual transition can be detected in
advance of the transition itself to provide anticipatory
sensing of the transition, and this phenomenon is central
to the concept of this invention.
The signal represented by wave form 70 is applied
to comparator circuit 54 which also receives a re~erence
voltage VTef from source S6. As seen in Fig. 3B, the
reference voltage is selected to correspond to an ampli-
tude of wave form 70 located at a position in advance of
the peak 72. Comparator 54 will respond to coincidence
of the amplitude of the signal 70 with Vref to generate
a control signal at an output terminal 55 thereof at a
time when the tape is positioned with the leading bit 25
of the preamble slightly in advance (i.e., up stream) of
the write head. This time interval is represented in Fig.
3B by the symbol ~ and permits the logic and control
circuit 36 to respond to the receipt of the control signal
from comparator 54 by actuating the write driver 60
slightly prior to or at essentially the same instant that
the peak 72 is in registry with the write head, to thereby
initiate the recording of the new record at that instant,
commencing with the standardized preamble, from data
source 32.
Thus, the new preamble will be written essen-
tially directly over the old preamble, followed by the
new record. Since the interval y corresponds to a tape
.~
movement of up to only ten microns, depending on the
reference voltage selected, the slight forward shifting of
-11-
105f~498
1 the new record is insignificant since the inter-record ~ap
is at least 17.8 mm and frequently more. As the tape con-
tinues past the write head, therefore, a new preamble
accompanied by a new record from source 32 is written
S over the old record, thereby completing the desired
"insertion" or reprogramming of the record involved.
It should be noted that in the preceding descrip-
tion words such as "recording head", "read head", "write
head", "gap'!, etc. are all used in varying senses and
varying connotations. It should be understood, however, that
in the following claims the words "gap" and "head" mean
substantially the same thing, i.e., the recording or
reproducing instrumentality, whether it be a particular
.~ gaping single multi gap head unit, a single head in a
multi head arrangement, or a single multi function gap in
a single head. Terms such as "read" and "write" should be
understood as denoting the primary purpose for which a
head or gap is intended to be used in a given application,
or at least a major such purpose, and not necessarily the
purpose for which it was conceived or devised by its
. ~
manufacturer, or the purpose which it may be most capable of
fulfilling in an actual sense.
It will become apparent to those skilled in the
art that many applications and modifications of the
present invention can be made. The reprogramming method
` and apparatus is applicable to ree~to-reel tape systems,
as well as to cassettes and other types of tape systems.
The system will also have application to recording
formats different than that described in the preferred
embodiment. Other types of detectors may be employed in
place of the threshold detector shown. These and other
:'.,
~05~498
1 modifications of the preferred embodiment will, however,
fall within the scope and spirit of the present invention
as defined by the appended claims.
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