JPH0722381B2 - Skew distortion prevention device in VTR - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a skew distortion prevention device in a VTR (video tape recorder), and particularly to 1/2 of the standard tape speed.
This is to prevent skew distortion that occurs when a video signal recorded at half speed is reproduced at a tape speed different from that at the time of recording.

[Prior Art] In general, a VTR is known in which two rotary heads having different azimuths are alternately scanned in a direction intersecting a running direction of a magnetic tape to form a recording track. . An example of the recording track of the video signal recorded by such a VTR is shown in FIG. FIG. 3 schematically shows the magnetic tape as viewed from the side in contact with the head, that is, from the magnetic body side. In the figure,
Reference numeral 1 is a magnetic tape, the running direction of which is indicated by an arrow 2. T1, T2, T3, T4, T5 indicate recording tracks of the video signal recorded on the magnetic tape 1, and these recording tracks correspond to one field of the video signal. Reference numeral 3 indicates the moving direction of the rotary head. The line 4 in these recording tracks indicates the position of the horizontal synchronizing signal of the video signal, and its direction schematically shows the angle of azimuth. That is, it is understood that these recording tracks are recorded by the rotating heads of different azimuths alternately.

The recording track is formed such that the start position of the field on the recording track is delayed by 1.5H (H is a distance corresponding to the interval of the horizontal synchronizing signal on the recording track) with respect to the start position of the previous field. The positions of the upper horizontal synchronizing signals are aligned and aligned. The diameter of the rotary drum, the speed of the rotary head, and the tape (running) speed are set so that such a recording track is formed. The track width of the rotary head may be equal to the width h1 of the recording track, or may be wide or narrow.

With this tape speed as the standard speed,
Fig. 4 shows the state (recording track pattern) when recording at 1/2 speed (half speed). In FIG. 4, reference numerals 1, 2, 3, and 4 represent the same reference numerals as those in FIG. t1 to t6 represent recording tracks.
Also in this case, the track width of the rotary head may be equal to the width h2 of the recording track, or may be wide or narrow, but it is desirable that the track width is 1/2 as compared with the case of FIG.

In the case of FIGS. 3 and 4, the length of the recording track is actually longer than one field, but the rotary head is switched at the timing of one field. It is drawn.

In the case of the standard speed of FIG. 3, the field start between adjacent recording tracks is 1.5H as described above, but in the case of the half speed of FIG. 4, it is half of that, 0.75H.
Is.

Next, description will be made on the case of reproducing at a tape speed different from the tape speed at the time of recording, for example, a tape speed five times as high as that at the time of recording. In FIG. 3, reference numeral 5 indicates the locus of the rotary head when the tape is reproduced at a tape speed which is five times as high as that at the time of recording. There is. The locus 5 has a reproduction output obtained when the rotary head to be scanned is on the recording tracks T1, T3, T5 of the same azimuth as the rotary head, and the portion on the locus 5 where the reproduction output is obtained is shaded. It is given and shown.

The locus 5 and diagonal lines are also drawn in FIG.

By the way, in the case of the standard speed shown in FIG. 3, the positions of the horizontal synchronizing signals shown by the line 4 are aligned at the boundary where the rotary head moves from the recording tracks T1 to T3 and from T3 to T5. Therefore, the intervals of the horizontal synchronizing signals of the reproduced video signals are also uniform, but in the case of the half speed shown in FIG. 4, the intervals of the horizontal synchronizing signals of the reproduced video signals are not uniform. That is, in the case of FIG. 4, the horizontal sync signal positions of the recording tracks t1, t3, t5 of the same azimuth have a shift of 1 / 2H, as can be seen from the shift of the start position of the field by 1.5H. , Recording track t1
From t3 to t3 and from t3 to t5, the positions of the horizontal synchronizing signals have irregular periods, and the intervals of the horizontal synchronizing signals of the reproduced video signal are also irregular. When this reproduced video signal is viewed on a television, the screen is distorted when the intervals of the horizontal synchronizing signals are not uniform, and the distortion of this screen is generally called skew distortion, and that time is called skew jump.

Conventionally, in order to prevent the above skew distortion, the device (circuit) shown in FIG. 5 has been used. In FIG.
Reference numerals 6a and 6b denote rotary heads, respectively, which have different azimuths. This rotary head has a track width of 1/2 compared to the rotary head used at the standard speed described in FIG. 3, and the position of the working gap is (1/2 +
n) deviated by H (n is an integer). Of these rotary heads 6a and 6b, the rotary head 6a and the rotary head 12a used at the standard speed are shown in FIG. Although not shown in the same manner as 12a for the rotary head 6a, the position of the operating gap is (1 /
There is also a rotary head offset by 2 + n). 7a, 7
Reference numeral b is a preamplifier, which amplifies the reproduction output signals from the rotary heads 6a and 6b to the operation level of the subsequent circuit. 8 is a video signal processing circuit, 9 is a skew detection circuit for detecting a skew jump position, 10 is a delay circuit for delaying the video signal from the video signal processing circuit 8 by 1 / 2H, and SW1 is from the preamplifiers 7a and 7b. A switch SW2 for selecting a video signal and supplying it to the video signal processing circuit 8 selects the through signal from the video signal processing circuit 8 and the 1 / 2H delay signal passed through the delay circuit 10 and outputs it from the output terminal 11. It is a switch.

The switch SW1 is switched for each field by the well-known head switching pulse shown in FIG. 6A, and the switch SW2 is output by the skew detection circuit 9 (shown in FIG. 6C described later). Can be switched.

Next, the operation of the skew distortion prevention device shown in FIG. 5 will be described. The rotary head 6a is the recording track of FIG.
If the same azimuth as T1 is used, the switch SW1 is the 6th
The rotary head 6a is switched by the pulse shown in Fig. (1).
Is switched to the solid line side when scanning over the magnetic tape 1, and is switched to the broken line side when the rotary head 6b is scanning over the magnetic tape 1. When the rotary head 6a scans along the trajectory 5 shown in FIG. 4 while traveling at a tape speed five times as high as that of recording on the magnetic tape 1, the envelope waveform of the reproduction output obtained from the rotary head is shown in FIG. It becomes like (2). The reproduction output passes through the preamplifier 7a and is input to the video signal processing circuit 8 via the switch SW1. The video signal processing circuit 8 extracts the horizontal synchronizing signal and supplies it to the skew detecting circuit 9. When the skew detecting circuit has irregular periods of the input horizontal synchronizing signal, the pulse shown in FIG. 6 (3) is generated. Output. On the other hand, the video signal that has passed through the video signal processing circuit 8 is not passed through the delay circuit 10 or is passed through the delay circuit and is delayed by 1 / 2H and is selected by the switch SW2 to reach the output terminal 11. Rotating head 6
Switch SW2 when a is scanning the recording track t1
Is switched to the side indicated by the solid line, and the video signal processing circuit 8
The video signal from is output to the output terminal 11 as it is.
When the rotary head 6a advances and moves from the recording track t1 to t3, the horizontal sync signal shifts by 1 / 2H.
Output is inverted and switch SW2 is switched to the broken line side,
The H-delayed video signal is output, and as a result, the periods of the horizontal synchronizing signals become uniform. When the rotary head 6a further advances and moves from the recording track t3 to the recording track t5, a skew jump occurs again, the output of the skew detection circuit 9 is inverted and becomes the solid line side, and as a video signal in which the cycle of the horizontal synchronizing signal is aligned. Is output. In this way, skew distortion on the TV screen can be prevented.

[Problems to be Solved by the Invention] In the skew distortion prevention device described above, the delay circuit 10 is used. However, this delay circuit is expensive, and there is a drawback that the VTR becomes expensive.

The present invention stopped the use of the expensive delay circuit described above and was provided in this type of VTR. Working gap is (1/2 + n)
An inexpensive skew distortion prevention device is provided by using a rotary head that is offset by H.

[Means for Solving the Problems] In order to solve the problems described above, the present invention alternately uses a first rotary head or a second rotary head having different magic masses in a direction intersecting the running direction of a magnetic tape. The recording track is formed by scanning, and the standard speed and the standard speed are used as the tape speed.
It is possible to select a half speed that is 1/2 speed, and at the standard speed, the positions of the horizontal synchronizing signals of the video signals on the adjacent recording tracks are aligned and arranged, At the time of speed, the VTR is such that the position of the horizontal synchronizing signal on every other recording track with the same azimuth is shifted by 1 / 2H, and the azimuth is the same as that of the first rotary head described above, and Each of the second rotary heads, wherein the working gap with the first rotary head is offset by a distance (1/2 + n) H, and the track width of the rotary head is about 1/2 of that of the first rotary head.
The second rotary head is used for recording / reproducing at half speed, and when the video signal recorded at the above half speed is reproduced at a tape speed different from that at the time of recording. In a VTR that is equipped with a skew detection circuit that detects the unevenness of the horizontal sync signal that occurs in the VTR and is adapted to cope with the unevenness of the horizontal sync signal, the video signal recorded at the half speed is not recorded. When playing back at different tape speeds, when the skew detection circuit detects an irregularity of the horizontal synchronizing signal, the first rotary head and the second rotary head are selected to cope with the irregularity. It is provided with a selection means to be used later.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG.
In FIG. 1, the same reference numerals as those in FIG. 5 described above indicate the same elements, and thus detailed description thereof will be omitted. 12a, 1
Reference numeral 2b indicates a rotary head, and the position of the working gap is (1/2 +) relative to the rotary heads 6a and 6b.
n) It is offset by H, and the track width is for a standard speed of double. 13a and 13b are preamplifiers and rotary heads
The reproduction output from 12a and 12b is amplified to the operation level of the circuit in the subsequent stage. SW3 and SW4 are switches, which select the output video signals from the preamplifiers 7a and 13a, 7b and 13b and supply them to the switch SW1. These switches SW3 and SW4 are switched by a T-type flip-flop 14. This T-type flip-flop 14 is triggered by the output of the skew detection circuit 9.

In the above-described embodiment, when the video signal is reproduced at the tape speed which is 5 times as high as that at the time of recording, the fourth movement is performed by the rotary head 6a.
While scanning the recording track t1 in the figure, switch SW
1, SW3, SW4 are switched to the side shown by the solid line. When the rotary head 6a advances and moves from the recording track t1 to t3,
The cycle of the horizontal sync signal of the playback video signal becomes uneven,
A pulse shown in FIG. 6 (4) is obtained from the skew detection circuit 9, and this pulse triggers the T-type flip-flop 14. The output shown in FIG. 6 (5) is obtained from the T-type flip-flop by the trowel, and the switches SW3 and SW4 are switched to the side indicated by the broken line by the output pulse. By this switching, the rotary head 12a is replaced with the rotary head 12a.
Video signal from a preamplifier 12a, switches SW3, SW1
Is supplied to the video signal processing circuit 8 via. Rotating head
Since the operating gap of 12a is shifted by (1/2 + n) H as described above, there is no irregularity in the cycle of the horizontal synchronizing signal of the reproduced video signal, and therefore the skew detecting circuit 9
Since the output of is inverted instantaneously, the output pulse shown in FIG. 6 (4) has an extremely narrow pulse width. In this way, a video signal having a uniform horizontal synchronizing signal cycle is obtained from the output terminal 11. The T-type flip-flop 14
Holds the state of any of the switches SW3 and SW4 from the time the output of the skew detection circuit 9 is inverted to the time it is next inverted.

In the above embodiment, the video signal that has passed through the switches SW3 and SW4 that can be switched by the T-type flip-flop is selected by the switch SW1. However, as shown in FIG. 2, it is selected by the switches SW5 and SW6 that are switched by the head switching pulse. Switch SW7 that can switch the video signal generated by T-type flip-flop
You may make it select by. Incidentally, in FIG. 2, the same reference numerals as those in FIG. 1 indicate the same components.

In the above embodiment, the start position of each field of the adjacent recording tracks is deviated by 1.5H, and the magnetic tape is wound around the head drum equipped with four rotary heads over about 180 °.
The present invention was carried out on a TR, but the present invention does not use a VHS tape in which a magnetic tape is wound around a head drum over 270 °.
It is suitable for application to a VTR called -C. This VHS
-C is equipped with four standard speed rotary heads at 90 ° intervals on the head drum. Adjacent rotary heads have different azimuths, but the rotary head and track width are about 1/2. , The position of the working gap is (1/2 +
n) Have rotating heads for each half speed apart H.

Further, although omitted in FIGS. 1, 2, and 5, the known rotary transformer is interposed between the rotary head and the preamplifier.

[Effects of the Invention] As described above, the present invention alternately scans in the direction intersecting the running direction of the magnetic tape 1 by the first rotary heads 12a and 12b or the second rotary heads 6a and 6b having different azimuths. To form recording tracks T1 to T5 or t1 to t6.
It is possible to select half speed, which is 1/2 speed, and at the standard speed, adjacent recording tracks T1 ~
The positions of the horizontal synchronizing signals of the video signal on T5 are aligned and lined up, and at the half speed, every other recording track t1, t3, t5 or t2, t4, t6 with the same azimuth is horizontal. In the VTR in which the position of the synchronization signal is shifted by 1 / 2H, the azimuths are the same as those of the first rotary heads 12a and 12b, and the working gap with the first rotary head is a distance ( 1/2 + n) H (n is an integer), and the track width of the rotary head is the same as that of the first rotary head 12a,
With each second rotary head 6a, 6b which is 1/2 of 12b,
The second rotary head is not used for recording / reproducing at half speed, and horizontal synchronization that occurs when the video signal recorded at the half speed is reproduced at a tape speed different from that at the time of recording. In a VTR that is equipped with a skew detection circuit 9 that detects the unevenness of the signals and copes with the unevenness of the horizontal synchronizing signal, a tape speed different from that at the time of recording the video signal recorded at the half speed described above. When the horizontal skew signal is detected to be non-uniform by the skew detection circuit 9 during reproduction by the above-mentioned method, the above-mentioned first method is provided in order to cope with the non-uniformity.
Since the switch SW3, SW4, SW5, SW6 and other selection means are used to selectively use the rotary head and the second rotary head, skew distortion can be prevented without installing an expensive delay circuit as in the conventional VTR. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment, and FIG. 3 is a schematic diagram showing recording tracks on a general magnetic tape at standard speed. FIG. 4 is a schematic diagram showing recording tracks on a magnetic tape at a half speed, FIG. 5 is a block diagram showing a conventional skew prevention device, and FIG. 6 is a diagram for explaining the operation of FIGS. 1 and 5. A time chart, FIG. 7 is a schematic front view of a rotary head block of a conventional device. 6a, 6b, 12a, 12b: rotary head, 9: skew detection circuit, SW3,
SW4, SW5, SW6: Switches.

Claims (1)

[Claims] 1. A direction crossing the running direction of a magnetic tape,
A first rotary head having a different azimuth or a second rotary head having a different azimuth is alternately scanned to form a recording track.
It is possible to select a half speed that is 1/2 speed, and at the standard speed, the positions of the horizontal synchronizing signals of the video signals on the adjacent recording tracks are aligned and arranged, At speed, the VTR is in a state in which the position of the horizontal sync signal on every other recording track with the same azimuth is shifted by 1 / 2H (H is a distance corresponding to the interval of the horizontal sync signal on the recording track). The azimuth is the same as that of the first rotary head described above, the working gap with the first rotary head is displaced by a distance (1/2 + n) H (n is an integer), and the track of the rotary head is About 1/2 the width of the first rotary head
When the recording / reproducing operation is performed at half speed, the second rotating head is used, and the video signal recorded at the half speed is recorded. The VTR is equipped with a skew detection circuit that detects the unevenness of the horizontal sync signal that occurs when the tape is played back at a tape speed different from that of the VTR. In reproducing the recorded video signal at a tape speed different from that at the time of recording, when the skew detection circuit detects an irregularity of the horizontal synchronizing signal, the first rotary head described above is provided to cope with the irregularity. A skew distortion prevention device in a VTR, comprising: selecting means for selecting and using the first rotary head and the second rotary head.