Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to a recording and/or playback apparatus
for video signals, equipped with a rotary head system which trackwise scans
a record carrier and which comprises at least one recording and/or playback
head and at least one erase head for trackwise erasing a recorded video
signal.
According to the invention there is provided a recording and/or
playback apparatus for video signals of the type wherein a rotary head system
transversely scans the entire width of a record carrier in a plurality of
parallel tracks, the rotary head system comprising a recording head and/or
playback head and an erase head for transversely erasing a recorded video
signal, the improvement wherein the apparatus further comprises an additional
stationary recording and/or playback head longitudinally scanning the record
- carrier along an additional track that crosses the path of the transversely
recorded tracks, means for phase locking field synchronieation pulses of
said video signal to the angular position of said rotary head, said erase
head being angularly displaced with respect to said recording head whereby
the erase head initiates the scan of a first track on said carrier a pre-
determined first delay time after the recording head initiates the scan of
a further track, terminal means for receiving timing pulses synchronized
with the angular position of said rotary head sysstem, delay means connected
to said terminal means for converting said timing pulses into a blanking
pulse coincident with the scan of the erase head across said additional track,
a source of erase signals, AND;,gate means connecting said erase signal source
to said erase head and connected to said delay means for conducting said
erase signals to said erase head in the absence of said blanking pulse and
for blocking qaid erase signals to said erase head in response to the
presence of said blanking pulse,
This ensures that signals possibly recorded in the further track
are not affected by a trackwise erasure previous to a trackwise recording of
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a video signal to be recorded.
To obtain the actuation delay for the switching device in the
simplest possible manner it appears to be advantageous when the switching
device is constituted b~ two series-connected switching stages, the first
switching stage which follows the pulse source having a switching time which
substantially corresponds to the time interval '2 1 from the instant that a
pulse from the pulse source appears until the instant at which the erase
head reaches the further track to be crossed, the second switching stage
which is controlled by said first switching stage having a switching time
which substantially corresponds to the time interval ~2 required by the
erase head for scanning the further track to be crossed, and the gate circuit
interrupting the transmission path to the erase head during the operation
of the second switching stage.
Furthermore, it is found to be very advantageous for the embodiment
of the pulse source of an apparatus according to the invention when an
existing apparatus stage which carries the field s~nchroni~ing
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pulses is directly used as a pulse source. This obviates the use of a
separate pulse source in the apparatus, thus making the apparatus simpler
` and cheaper.
The invention will be described in more detail with reference to
two embodiments shown in the accompanying drawing to which the scope of the
invention is not limited. In the drawing:
Figure l shows the circuit arrangement of an apparatus according
to the invention which includes a separate pulse source,
Figure 2 shows the track configuration of a record carrier with
reference to which the operation of the apparatus of Figure l is described,
and
Figure 3 shows the circuit arrangement of a further suitable
embodiment of the apparatus according to the invention, in which the pulse
source is constituted by an apparatus stage which carries the field syn-
chronizing pulses.
The embodiment of Figure l is a recording apparatus for video
signals, which is equipped with a rotary head system l, which comprises two
recording heads 2 and 3 and two erase heads 6 and 7 which proce~e the
recording heads 2, 3 viewed in the direction of rotation 4 of the head sys-
tem l and which are staggered relative to the recording heads 2, 3 in thedirection of the axis 5 of the system l. This arrangement of the heads
2, 3, 6, 7 of the head system l in a conventional manner ensures that the
two associated heads 2, 6 and 3, 7 scan the same obliquely arranged tracks
lO, ll, 12 etc. (see Figure 2) of the record carrier ô which is helically
wound around the rotary head system l, as is schematically illustrated by
Figure l and which in the "normal winding" mode is advanced in the direction
of the arrow 9 by a drive shaft, not shown.
For driving the rotary head system l the apparatus incorporates
a motor 13 which is coupled to the shaft 5 of the rotary head system l, the
Qpeed of qaid motor being controlled by a servo circuit l4 connected there-
to. An input 15 of the servo circuit 14 is connected to a tachogenerator
16 whlch 1s coupled to the shaft 5 of the héad system l. A further input 17
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of the servo circuit 14 is connected to an output 19 of a separator stage 20,
at which output the field synchronizing pulses 18 of a video signal to be
recorded are available. The separator stage 20 is connected to a signal
input 21 of the apparatus, to which input a video signal to be recorded can
be applied.
For applying a video signal to be recorded to the recording heads
2, 3 of the rotary head system 1, the apparatus includes a transmission path
22, schematically shown, whose input 23 is connected to the signal input 21
of the apparatus and whose output 24 is connected to the recording heads 2,
3 for example via a rotary transformer. The transmission path 22 in the
shown embodiment includes a recording signal stage 25 and a s~itch 26 for
starting a recording process.
The operation of the circuit arrangement described above will now
be described in more detail. A video signal to be recorded which is avail-
able at the signal input 21 of the apparatus is fed to the separator stage
20, in which the field synchronizing pulses 18 are extracted from the video
signal to be recorded, which pulses are applied to a further input 17 of the
servo circuit 14 as the desired signal. The signal produced by the tacho-
generator 16 is fed to the input 15 of the servo circuit 14 as the measured
signal. In the servo circuit 14 the desired signal and the measured signal
are compared with each other and a control signal is produced which is a
measure of the difference between these signals. The control signal influ-
ences the motor current and motor voltaee so as to maintain the speed of
the motor 13 constant at a specific value.
The video signal is moreover fed from the signal input 21 of the
apparatus to the recording signal stage 25, where the video signal is pro-
cessed for subsequent registration. In the case of a black-white-video sig-
nal this processing may, for example, be frequency modulation. In the case
of a colour video signal this signal is, for example, split up into a
luminance signal and a chrominance signal in the recording signal stage 25,
after whlch the lu~inance signal is frequency modulated and the chrominance
~lgnal ls transpo~ed, the frequency-modulated luminance slgnal and the
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transposed chrominance signal being subsequently recombined. The processed
video signal is available at the output of the recording signal stage 25.
By the actuation of the switch 26 the apparatus is seto to the
"recording" mode and the transmission path 22 for the video signal is closed,
so that the processed video signal is fed to the r~cording heads 2, 3 of the
rotary head system 1 for the trackwise recording on the record carrier ô.
During the recording process the recording heads 2, 3 of the rotary head
system 1 consecutively scan the tracks 10, 11, 12 etc. which are arranged
obliquely on the record carrier 8 which advances in the direction of the
arrow 9 and record the applied video signal to be recorded in said tracks.
This embodiment furthermore comprises a stationary magnetic head
27, which scans a further track 28, which extends in the longitudinal direc-
tion of the record carrier 8 and which is crossed by the tracks 10, 11, 12
etc., in which the video signal is recorded. By means of the magnetic head
27 for example an audio signal, a control signal or a synchronizing signal
can be recorded in the further track 28.
Furthermore, an erase oscillator 29, via a transmission path 30
which includes a switch 31 for switching on an erasing process, can be con-
nected to the erase heads 6, 7 of the rotary head system 1 for example via
a further rotary transofmer, so that prior to a new recording a previously
recorded video signal on the tracks 10, 11, 12, etc., can be erased track-
wise.
The transmission path 30 for the erase signal now includes a gate
circuit 32 which is conducting in the rest position, whose input 33 is con-
nected to the erase oscillator and whose output 34 is connected to the erase
heads 6, 7 via the switch 31 for switching on the erasing process. For con-
trolling the gate circuit 32, a pulse source 35 followed by a switching
device 36 are provided, an output 37 of the pulse source 35 being connected
to an input 20 of the switching device 36 and an output 39 of the switching
device 36 being connected to a control input 40 of the gate circuit 32.
The pulse source 35 includeB a stationary scanning head 41 and
two magnets 42 and 43 disposed on the rotary head system 1, which during
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rotation of the head system 1 serve for producing pulses 44 in the scanning
head 41. By means of the servo system 13, 14, 16 for controlling the speed
of the rotary head system 1 the pulses 44 are locked to the field syn-
chronizing pulses 18 of the video signal to be recorded, which are applied
to the servo circuit 14. Thus, as is evident from Figures 1 and 2, there is
a time relationship between the instant at which the pulses 44 of the pulse
source 35 appear and the instant at which the field synchronizing pulses 18
appear (To)- Moreover, the pulses 35 appear in a fixed time relationship
with respect to a specific position 45 of the erase heads 6, 7 relative to
the further track 20 to be crossed, because the magnets 42, 43 and the
erase heads 6, 7 are arranged on the rotary head system 1 in a fixed spatial
position relative to each other.
The switching device 36 produced a pulse shaped switching signal
46 at its output 39, the beginning of the switching process of the switching
device 36 being delayed relative to the instant at which the pulses 44 from
` the pulse source 35, i.e. their leading edges, appear, by a delay time
` obtained with the aid of conventional delay means, which delay time sub-
stantially corresponds to a time interval T1 between the instant that a
pulse from the pulse source 35 appears and the instant at which the erase
20 head 6 or 7 of the rotary head system 1, whichever is first, reaches the
further track 28. The duration of the switching process of the switching
device 36 substantially equals a time interval T2, required by the erase
heads 6, 7 for scanning the further track 28 to be crossed.
By the actuation of the switch 31, which may be coupled to the
switch 26 for starting a recording process, a trackwise erasing process is
initiated. As a result, the erase signal from the erase oscillator 29 is
fed via the gate circuit 32, which is conducting in the rest condit~on, and -~
the closed switch 31 to the rotating erase heads 6, 7, which trackwise erase ~ -
a video signal that has been previously recorded on the record carrier 8.
At the instant at which for example the magnet 43 on the rotary head system
1 generates a pulse 44 in the scanning head 41, the associated erase head 7
is in the speci~ic position 45 relative to the further track 28 to be crossed
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as schematically shown in Figures 1 and 2. The resulting pulse ~4 is fed to
the switching device 36, which subsequently supplies the pulse-shaped switch-
ing signal 46 at its output 39, which signal relative to the instant at
which the leading edge of the pulse 44 appears is delayed by said time
and is continued during said time interval l2 The switching signal 46
blocks the gate circuit 32 via control input 40, so that the gate circuit
32 interrupts the transmission path 30 for the erase signal whilst the
erased head 7 scans the further track 28. After the time interval T2 the
gate circuit 32 becomes conducting again and closes the transmission path 30
for the erase signal, so that the trackwise erasing process is continued. A
similar process is repeated in a corresponding manner fOr the second erase
head 6 during the scanning of the next track.
The steps described hereinbefore thus permit a trackwise erasure of
a recorded video signal, the erasing process being interrupted whllst the
erase heads of the rotary head system scan a further track provided on the
record carrier. Thus, a previously recorded video signal can be erased
trackwise, without a signal recorded in the further track being erased.
As is evident from the above, the delay time before the beginning
of the switching process of the switching device can be obtained by means
of the switching device itself. Another posslbility is to design the pulse
source so thst the delay time Tl is directly determined by the duration of
the pulses from the pulse source. In that case the beginning of the switch-
in8 process of the switching device is defined by the trailing edges of the
pulses from the pulse source and the switching device performs an on/of
` operation the duration of which again corresponds to the time interval T2,
required by a rotating erase head for scanning the further track to be
';s crossed.
Similar steps have been taken in the embodiment of Figure 3. In
this apparatus the transmission path 22 for the video signals includes a
switch 50 for switching between the "recording~' and "playback" modes, which
in the "recording" mode electrically connects the recording stage 25 and in
the "playback" mode a playback stage 51 to the recording playback heads 2,
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3. The other side of the playback stage 51 is connected to a signal output52 of the apparatus.
The switch 50 is coupled to the switch 31 for starting a track-
wise erasing process and furthermore to two switches 53 and 54. In the
"recording" mode Q switch 53 connects the further input 17 of the servo
circuit 14, which input serves for applying the desired signal, to the out-
put 19 of the separator stage 20 which carries the field synchronizing
pulses 18 and in the "playback" mode to a reference signal source 55. In
the "recording" mode the output 19 of the separator stage 20 is further-
more connected to the magnetic head 27 via the switch 54. In the "play-
back" mode the switch 54 connects the magnetic head 27 to a terminal 56,
which is electrically connected to a servo system, not shown, for con-
trolling the speed of the drive shaft which advances the record carrier 8.
For recording a video signal which is applied to the signal input
21 of the apparatus the switch 60 is set to the position corresponding to
the "recording" mode described above. In this case the processes relating
to the processing of the video signal and the control of the speed of the ; ~-
;,` rotary head system are the same as those described with reference to the
embodiment of Figure 1. In addition to these processes, the field syn-
20 chronizing pulses 18 of the video signal to be recorded are fed to the
stationary magnetic head 27 via the switch 54, which head records said
pulse train in the further track 28 which extends in the longitudinal direc-
. tion of the record carrier 8.
For reproducing a recorded video signal the switch 50 is set to
I the position which corresponds to the "playback" mode. As a result, the
¦ video signal which is scanned from the recorded carrier 8 by the recording/
playback heads 2, 3 is applied to the playback stage 51 for further pro-
cessing. The video signal appearing at the output of the playback stage 51
is fed to the signal output 52 of the apparatus where it is avialable for
application to, for example, a television receiver.
In the "playback" mode pulses 57, which are produced by the
reference signal source 55 and which in this case may, for example, be
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derived from the mains frequency, are applied via the switch 53 to the ~ur-
ther input 17 of the servo circuit 14 as the desired signal, so that in this
mode the control signal for controlling the speed of the motor 13 is obtained
by comparing the pulses supplied by the tachogenerator 16 with the pulses 57
supplied by the reference signal source 55.
In the "playback" mode the field synchronizing pulses recorded in
the further track 28 are scanned by the magnetic head 27 and via the terminal
56 they are applied to the servo-system, not shown, which serves for con-
trolling the drive shaft for advancing the record carrier, as the actual
signal. The pulses 57 produced by the reference signal source 55 may then
also be applied to this servo system as the desired signal.
For example, if with such an apparatus a previously recorded video
signal from a certain point onwards is to be repalced by another signal to
j be recorded, the servo systems of the apparatus must be in the "playback"
mode whilst the apparatus is in the "recording" mode, in order to ensure that
the field synchronizing pulses previously recorded in the further track can
; maintain the synchronism of the record carrier at the transition from the
previously recorded video signal to the new video signal to be recorded.
However, before the new video signal is recorded, the previously recorded
20 video signal must be erased trackwise from the said point onw~rds. `
In the present embodiment the separator stage 20 which carries
the field synchronizing pulses directly serves as a pulse source 35. The
output 37 of the pulse source 35 is connected to the input 38 of the switch-
ing device 36, which in this case is formed by two series-connected switch-
ing stages 58 and 59. The start of the switching process of the first
switching stage 58 following the pulse source 35 is defined by the instants
at which the field synchronizing pulses 18 of a video signal to be recorded
appear, i.e. by their leading edges. The duration of the switching process
of the switching stage 58 substantially correspond to the time interval ~1
30 between the instant at which a field synchronizing pulse 18, i.e. its lead-
ing edge, appears and the instant at whlch the erase head 6 or 7 of the
rotary head sy~teM 1, whichever first scans the further track 28, reaches
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the further track 28. The beginning of the switching process of the second
switching stage 59, which is controlled by the first switching stage 58, is
determined by the trailing edge of the output signal 60 of the first switch-
ing stage 58. The switching time of the second stage 59 substantially cor-
responds to the time interval l2' required by the erase head for scanning
the further track 28 to be crossed.
When the switches 50, 53 and 54 are set to the position correspond-
ing to the "recording" mode, the switch 31 is closed so that in this mode a
previously recorded video signal is automatically trackwise erased prior to
a new recording. For this purpose the erase signal from the erase oscillator
29 is fed to the erase heads 6, 7 of the rotary head system 1 via the gate
circuit 32, which is conducting in the rest condition, and the switch 31.
In order to prevent the field synchronizing pulses recorded in the further
track 28 from being also erased by this erasing process, the transmission
path 30 for the erase signal is interrupted by the gate circuit 32, whilst
an erase head 6, 7 scans the track 28. For this the field synchronizing
pulses 18, which are available at the output 19 of the separator stage 20
and which are derived from the video signal to be recorded present at the
signal input 21 of the apparatus, are fed to the first switching stage 58
i 20 which feeds the control signal 60, which has a duration corresponding to the
said time interval ~1' to the second switching stage 59. The trailing edge
of the control signal 60 now starts the second switching stage 59, after
which the switching signal 46, which has a duration corresponding to the ; --
said time interval T2, appears at the output 39 of the switching device 36
which also constitutes the output of the second switching stage 59. The
switching signal 46 blocks the gate circuit 32 via the control input 40,
thus interrupting the transmission path 30 from the erase oscillator 29 to
the erase heads 6, 7. After the time interval l2 has elapsed the switching
signal 46 is discontinued and the gate circuit 32 becomes conducting again,
so that the trackwise erasing process proceeds. This allows a trackwise
erasure, the erasing process ~being interrupted whilst the erase heads of the
rotary head system scan the further track on the record carrier.
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In the recording and/or playback apparatus of Figure 3 an existing
stage which carries field synchronizing pulses, viz. the separator stage 20,
is directly employed as a pulse source. This step obviates the need for a
separate pulse source, which for example in Figure 1 comprises a magneto-
motoric or a photoelectric-pulse generator, which obviously leads to a
simpler and cheaper design. This step furthermore yields the additional
advantage that tolerance errors caused by magneto-motoric or photoelectric
pulse generators ~re eliminated, thus also increasing the accuracy,
When the switching device for controlling the gate circuit employs
two separate switching stages, this moreover yields the advantage that the
switching time of each switching stage can be selected or adJusted indepen-
dently of the switching time of the other switching stage. As a result, the
; interruption of the track-wise erasing process can simply be adapted to the
width and the arrangement of the further track. Furthermore, it enables the
duration of the interruption of the erasure process to be adapted to the
required degree of certainty that a signal recorded in the further track
should not be erased.
It is obvious that a series of modifications to the embodiments
described hereinbefore can be realized within the scope of the invention,
specifically with respect to the circuit design of the pulse source, of the
switchine device ~nd o~ the gate circuit.
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