Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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_ ~netic Tape Reproducing System
Back~3round of the Invention
This invention relates to a magnetic tape reproducing
system, and more particularly to a magnetic tape reproducing
system for reproducing television signals which are recorded
longitudinally Oll a magnetic tape in successive fields. ;`
Heretofore, there have been proposed several methods
for presenting a still picture or a slow motion picture, for
example by reproducing the same field of television signals,
which are recorded on a magnetic tape in the longitudinal dir- ` `
ection thereof, a plurality of times successively by a plurality -
of rotary reproducing heads. ~`
However, in a conventional magiletic recording and re-
producing apparatlls for providing such a still picture by suc
cessively reproducing the same field of the video signals, there
is a problem that owing to deviation of the horizontal synchronizing
signal of the video signal there is caused a skew distortion and
it results in poor picture quality.
Therefore, an object of the present invention is to
20- provide a novel and improved magnetic recording and reproducing
apparatus for presenting a still picture or a slow motion picture
having a better picture quality. -
Another object of thP invention is to provide a novelmagnetic tape reproducing system for reproducing a still picture
which is stable and has no skew distortion, from the video signals
recorded in the longitudinal direction on a magnetic tape in suc-
cessive fields.
A further object of the invention is to provide a novel
magnetic tape reproducing system for presenting a stable still
picture by using a plurality of rotary reproducing heads.
These objec~s are achieved by providing a magnetic tape
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reproducing system according to the present invention, which com-
prises a magnetic tape on whic~ video signals are recordea in
successive fields of a unit length in the longitudinal direction
of said magnetic tape, each field of said video signals containing
horizontal synchronizing signals, a rotating disc, a d`riving means
for rotating said rotating disc, and a plurality of reproducing
magnetic heads which are placed on the periphery of said rotating
disc at equal angular intervals relative to each other, each of
said plurality of reproducing heads being arranged so as to re-
produce one complete field of said video signals and being arrangedso that the distance between two gaps of two adjacent heads is
equal to an integral multiple of the distance along the tape cor-
responding to a period of said horizontal synchronizing signals.
The integral number is preferably around 262.
Where there are three reproducing rotary magnetic heads, the
length of the magnetic tape which is wound around the rotating ~
disc can extend more than 240 degrees around the disc. `
Brief Description of the Drawings
These and other objects and features and advantages of
the invention will be apparent from a consideration of the following
detailed description and reference to the accompanied drawings,
wherein: - `
Fig. 1 shows the head assembly of three rotary magnetic
heads and the magnetic tape for explaining an embodiment of the
invention;
Fig. 2 shows a part of the magnetic tape used in the
apparatus according to the invention showing the track pattern
of the tape, on which the signals of fields extracted intermittently -
from the video signals are recorded successively in the longitudinal
direction of the tape by the assembly of three rotary heads shown
in Fig. l; and
Figs. 3(a) to 3(c) show the patterns of the video signals
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reproduced from the magnetic tape shown in Fig. 2 by the three
rotary magnetic heads, respectively, and Fig. 3(d) shows the pattern :~
of the video signal synthesized from the effective parts of the
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reproduced video signals 3(a~ to 3(c).
Detailed Description of the Preferred Embodiment
Referring to Figs. 1 to 3, an embodiment o~ the invention
will be described in detail which uses three rotary magnetic heads.
Fig. 1 shows the relation between the head assembly ;~
having three rotary magnetic heads and a magnetic tape, wherein the
magnetic tape designated by a reference numeral 1 is moved in the
direction of arrow V by fixed guide rollers 2 and 3. The rotary
head assembly 5 comprises a rotary disc 6 and three magnetic heads ~ ~;
4a, 4b and 4c arranged at equal angular intervals of 120 degrees
along the periphery of the rotary disc 6, and the disc 6 is rotated
in the direction of arrow ~.
The driving means for rotating the rotary disc 6 is a
motor M. The moving means for moving the magnetic tape 1 is omitted ~
herewith for simplifying the description. Further, although the `
direction of rotation is optional in the system according to the
invention, the following description is for rotation in the dir-
ection of the arrow ~. -
Referring to Fig. 2, there is shown a track pattern of
each of the fields 7a, 7b, 7c and 7d of the video signals which
are for one field and which are extracted intermittently from
the video signals and recorded successively in the longitudinal
direction of the magnetic tape 1 by the three rotary magnetic heads
of Fig. 1. In case of Fig. 2 there exists between the two adjacent
recorded field patterns a narrow portion where the signal is not
recorded. However if the period for sampling one field of the
video signal is shortened a little during recording, there exists
a portion where parts of the two adjacent fields overlap instead
of the portion where no signal exists, as described. However,
as will be obvious from the description presented hereinafter, the
fundamental operation of the system of the invention is substantially
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the same for both cases described above, i.e. where there is a
portion having no signal or where there is an overlapping portion,
and so the following description is presented for the case shown
in Fig. 2.
Further, in order to provide the recorded track pattern
as shown in Fig. 2, it is not necessary to use three rotary magnetic
heads. It is of course possible to use a system having one rotary
head, two rotary heads or a fixed head.
Figs. 3(a) to 3(c) show the output signals reproduced by
the rotary magnetic heads 4a, 4b and 4c, respectively during move-
ment of the magnetic tape on which the video signals are recorded
as shown in Fig. 2 around the disc 6 having the three rotary mag-
netic heads thereon. Fig. 3(d) shows the output signal which is
synthesized from the effective parts of each of the reproduced -
signals 3(a) to 3(c).
As shown in Fig. 1, the length of the magnetic tape 1
wound around the rotary disc 6 is at least as long as the length
of two fields of the recorded video signals shows in Fig. 2, i.e.
the tape extends 240 degrees or more around disc 6. Therefore,
each of the signals of Figs. 3(a), 3(b) and 3(c) reproduced
by the magnetic heads 4a, 4b and 4c, respectively contains video
signal information for one complete field. In Figs. 3(a) to 3(b), -
such a complete one field, the field 7b as an example, is in-
dicated by hatching.
Fig. 3(d) shows a tr~n of successive fields 7b, one of
the fields of the recorded video signal, which is continuously
- synthesized for providing a still picture signal. The signal 3(d)
is provided by switching the reproduced signals from the magnetic ~-
heads 4a, 4b and 4c in turn at the times Al, A2, A3,...., as shown
in Fig. 3. As a practical means for obtaining the synthesized
signal of Fig. 3(d), for example, the reproduced signals from the
rotary magnetic heads 4a, 4b and 4c are taken out of the heads by
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a conventional slip-ring brush or rotary transformers, and on
detecting a control signal such as a vertical synchronizing signal
contained in each field of the signals, the si~nals ~rom each o~
the magnetic heads are synthesized by driving a well-known suitable
switching circuit by that detected control signal.
The signal of Fig. 3(d) is a signal for a still picture
of one field, and if the horizontal synchronizing signals in each
field are not related correctly and continuously at the times
Al, A2, A3, .. when the output signals from each of the magnetic
heads are switched, there is caused, as well known, so-called skew
distortion which usually results in a poor picture which is dis-
torted to the right or left at the upper part of the picture on
a monitor TV receiver.
According to the magnetic tape reproducing system of
the invention, such a skew distortion can be eliminated by arranging
the distance Q along the periphery of the disc 6 between the two
adjacent heads of the plurality of reproducing magnetic heads to be
n ~n is an integer around 262, for example 262 or 263) times the
length corresponding to the period of the horizontal synchronizing
signal synchronizing signal. This relation of lengths is accomplished
by adjusting the speed of movement of the magnetic tape during re-
cording, the rotating speed of the recording magnetic heads and
the radial distance thereof, from the center of rotation and the
radial distance of the reproducing magnetic heads from the center
of rotation thereof, and by relating these values to each other.
This aspect of the invention is described in more detail in the
following.
There will first be considered what occurs around the
switching time A3 in Fig. 3, that is the junction point A3 bet-
ween the still picture signals provided by synthesizing the re-
produced signals from each of the rotary magnetic heads 4a, 4b and 4c.
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At a portion a little before the point A3, the signal of Fig. 3(d)
is the output signal from the head 4b, and at a portion a li-ttle
after the point A3, the signal of Fig. 3(d) is the output signal
from the head 4c. As for the signal of Fig. 3(d) indicated at
the point A3, the reproduced signal from the head 4c has a phase
delayed with respect to that of the signal reproduced from the head
4b, and the amount of the phase delay corresponds to the distance
on the magnetic tape between two points wher the air gaps of the
- head tips of the heads 4b and 4c contact the tape, respectively
while reproducing. The distance between these two points is des-
ignated by Q in Fig. 1. That is, the signal of Fig. 3(d) represents
the condition that the signal for the same field is always provided
at a phase delayed by an amount corresponding to the distance at
each of the connecting points.
Accordingly, when the length Q coincides with integral
multiple of the length corresponding to the period of the horizontal
synchroni~ing signals, the horizontal synchronizing signals are
correctly and continuously related to each of the junction points
of the still picture signal 3(d). Therefore, skew distortion is
never caused; The same is true for the other junction points
Al, A2, A4, ... besides A3.
When, during reproducing, the three rotary magnetic heads
4a, 4b, and 4c in Fig. 1 are arranged correctly at the equal in-
tervals of 120 degrees, the above mentioned length Q between the
two points where the air gaps of the head tips of each two adjacent
magnetic heads contact with the magnetic tape is expressed as fol-
lows:
Q = ~ ................... (1)
wherein yp is the radial distance of the reproducing rotary magnetic
heads from the center of rotation. On the other hand, the mutual
speed of the magnetic tape and the rotary magnetic heads is expressed
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as (~RyR ~ )r in which V~ is the speed of movement of the
magnetic tape during recording, ~ is the speed of rotation of
the recording rotary magnetic heads and YR is the radial distance
thereof from the center of rotation. Therefore, for hori~ontal
synchronizing signals having a period TH, the signals in that
per.iod T~I are recorded on the magnetic tape in a length of
(~RY~ ~ VR)TH-
For the condition for removing skew distortion, that isfor making the length Q equal to an integral multipl.e of the length
corresponding to the period of the horizontal synchronizing signals,
the following equation must be satisfied:
2~yp = n(~R~R + VR)TH ---........... (2)
in which n is an optional integer. As the period of the signal ;
for one field is around 262, it is of course desirable that n be
an integer around 262, for example 261, 262 or 263.
The above equation (2) is of couxse also applicable for
the case in which the speed VR of the magnetic tape during re-
cording is zero, and for a fixed head system ~here YR is zero. ~-
Further, although in the above embodiment the description
has been for the case in which the switching of the reproduced ::
signals from each of the magnetic heads is carried out, as will ~;
be obvious from Fig. 3(d), in the same field of the reproduced
signal, other ways are also possible for satisfying the above -.. .
conaition. For example, when recording the signals of one field
extracte~ by sampling on the magnetic tape, a signal a little
longer than one field may be recorded, or it is also of course
possible that during reproducing the value of n in the equation
(2) may be set to a value smaller than 262. Although the still
picture signal provided in such a way is not a signal of the normal
standard TV system used in Japan or the U. S. A., it does not cause
any trouble during the di.splay of the si.gnal on a conventional
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monitor TV receiver. 1~3984S
Further, although the system has been described herein-
before for three rotary magnetic heads, the subject of the in-
vention can be used with other optional members of rotary heads.
There has been described hereinbefore a preferred em-
bodiment of the invention, and it is apparent that various modi-
fications may be made without departing from the spirit and scope
of the invention which is defined by the following claims.
