JPH02180480A - Skew prevention device for vtr - Google Patents

Abstract

PURPOSE:To offer a skew prevention device at a low cost by alternatively executing scanning with a first head or a second rotary head whose azimuth is mutually different, in a direction intersecting with the scanning direction of a magnetic tape and forming a recording track. CONSTITUTION:When a video signal is regenerated at the five-fold recording speed as high as a recording time and a recording track t1 is scanned by a rotary head 6a and switches SW1, SW3 and SW4 are switched to a side shown by a full line. When the rotary head 6a is advanced and moved from the recording track t1 to a track t3, the period of the horizontal synchronous signal of the regenerated video signal is disordered and a pulse is obtained from a skew detection circuit 9. Then, the switches SW3 and SW4 are switched to a side shown by a broken line. By this switching, instead of the rotary head 6a, the video signal from a rotary head 12a is supplied through a preamplifier 12a and switches SW3 and SW1 to a video signal processing circuit 8. Thus, the disorder of the cycle for the horizontal synchronous signal of the regenerated video signal is eliminated.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a skew distortion prevention device in a VTR (video tape recorder), and particularly to a skew distortion prevention device for a VTR (video tape recorder).
This is designed to prevent skew distortion that occurs when a video signal recorded at a half speed of /2 is played back at a tape speed different from that at the time of recording.

[Prior Art] Generally, a VTR is known in which recording tracks are formed by alternately scanning two rotating heads with different azimuths in a direction intersecting the running direction of a magnetic tape. . FIG. 3 shows an example of a recording track of a video signal recorded by such a VTR. FIG. 3 is a schematic representation of the magnetic tape viewed from the side in contact with the head, that is, from the magnetic material side. In the figure, the symbol l is a magnetic tape, and its running direction is indicated by the arrow 2.
It is shown in TI, T2. T3. T4. T
Reference numeral 5 indicates recording tracks of video signals recorded on the magnetic tape 1, and each of these recording tracks corresponds to one field of the video signal. 3 indicates the direction of movement of the rotary head. &14 in these recording tracks indicates the position of the horizontal synchronization signal of the video signal, and its direction schematically indicates the azimuth angle. That is, it can be seen that these recording tracks were recorded by rotating heads with different azimuths alternately.

The start position of the field in the 8th recording track is 1.5H relative to the start position of the previous field (H is the distance equivalent to the interval of horizontal synchronization signals on the recording track).
The recording tracks are formed so as to be delayed, and the positions of the horizontal synchronizing signals on the recording tracks are aligned. The diameter of the rotating drum, the speed of the rotating head, and the tape (
(running) speed is set. The track width of the rotary head may be equal to the recording track @h1, or may be wider or narrower.

This tape speed is set as the standard speed, and the state when recording at 1/2 speed (half speed) is J! l (recording track pattern) is shown in FIG.
In the figure, numerals 1, 2, 3.4 indicate the same elements as those with the same numerals in FIG.

tl-t6 indicates a recording track. In this case as well, the track width of the rotary head is the recording track width h2
It may be equal to or wider or narrower, but the 31st!
It is desirable to set it to ]/2 compared to the case of I.

In the cases shown in Figures 3 and 4, the length of the recording track is actually longer than one field, but the rotating head is switched at the timing of one field. In the case of the standard speed shown in FIG. 3, the start of the field between adjacent recording tracks is 1.5H, but the 48th! For half speed I, it is half 0.75H.

Next, a case where reproduction is performed at a tape speed different from the tape speed at the time of recording, for example, five times the tape speed at the time of recording, will be described. In FIG. 3, reference numeral 5 indicates the trajectory of the rotary head when the tape is reproduced at five times the recording speed, and its starting edge coincides with the recording track Tl, and its ending coincides with the recording track T5. There is. The rotary head that scans this locus 5 has the same azimuth as the recording tracks TI, T3. A reproduced output is obtained when the position is on T5, and the portion on the locus 5 where this reproduced output is obtained is shown with diagonal lines.This locus 5 and the diagonal lines are similarly drawn in FIG. ing.

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 even at the boundaries where the rotary head moves from recording track T1 to T3 and from T3t)) to T5. Therefore, the intervals between the horizontal synchronizing signals of the reproduced video signal are also the same, but in the case of half speed shown in Fig. 4, the intervals of the horizontal synchronizing signals of the reproduced video signal are uneven. Put it away. That is, in the case of FIG. 4, recording tracks t1. of the same azimuth. t3. t5
As can be seen from the fact that the field start position is shifted by 1.5H, the position of the horizontal synchronization signal is 1/2H.
There is a shift from recording track t1 to t, 3, and then t3.
At the boundary from t5 to t5, the periods of the positions of the horizontal synchronizing signals become irregular, and the intervals of the horizontal synchronizing signals of the reproduced video signal become irregular. When this reproduced video signal is viewed on a television, the screen is distorted where the intervals of the horizontal synchronization signals are irregular, and this screen distortion is generally called skew distortion, and this phenomenon is called skew jump.

Conventionally, a device (circuit) shown in FIG. 5 has been used to prevent the above-mentioned skew distortion. In Figure 5,
Reference numerals 6a and 6b indicate rotating heads, which have different azimuths. The track width of this rotary head is 1/2 that of the rotary head used at the standard speed explained in Fig. 3, and the position of the operating gap is (+/2 + n)H (n is an integer). It's off by just that.

Among these rotary spatulas 1"6a and 6b, rotary spatula l"
Rotating spatula l"1 used when using Ga and the above standard speed
2a is shown in FIG. Similar to the rotary head 12a for the rotary head 6a, although not shown, a rotary head whose operating gap is shifted by (1/2+n) from the rotary head 6a is also provided. Preamplifiers 7a and 7b amplify the reproduced output signals from the rotary heads 6a and 6b to the operating level of the subsequent circuit. 8 is a video signal processing circuit; 9 is a skew detection circuit that detects a skew jump position; 10 is a delay circuit that delays the video signal from the video signal processing circuit 8 by 1/2H; SWI
SW2 is a switch that selects the video signal from the preamplifiers 7a and 7b and supplies it to the video signal processing circuit 8;
This switch selects the 1/2H delayed signal that has passed through 0 and outputs it from the output terminal 11.

The above-mentioned switch Sνl is switched for each field by a well-known head switching pulse shown in (1) of FIG. Can be switched.

Next, the operation of the skew distortion prevention device shown in FIG. 5 will be explained. If the rotary head 6a has the same azimuth as the 9-track truck Tl in FIG.
WI is switched by the pulse shown in FIG. 6(1), and when the rotating spatula +'6a is scanning the magnetic tape 1, it is on the solid line side, and when the rotating head 6b is scanning the magnetic tape 1, it is on the solid line side. It is switched to the dashed line side. When the magnetic tape l runs at five times the recording speed and the rotary head 6a scans along the trajectory 5 shown in FIG. (2) becomes as follows. This reproduced output passes through the preamplifier 7a and is input to the video signal processing circuit 8 via the switch S frame. This video signal processing circuit 8 extracts the horizontal synchronization signal and supplies it to the skew detection circuit 9. When the period of the input horizontal synchronization signal becomes irregular, the skew detection circuit generates a pulse as shown in FIG. 6 (3). Output. On the other hand, the video signal that has passed through the video signal processing circuit 8 either does not pass through the delay circuit 10 and is delayed by 1/2 H, and then is selected by the switch SW2 and reaches the output terminal II. When the rotary head 6a is scanning the recording track L1, the switch S22 is switched to the side shown by the solid line, and the video signal from the video signal processing circuit 8 is outputted to the output terminal 11 as it is. When the rotary head 6a advances and moves from the recording track opening to L3, the horizontal synchronizing signal is shifted by 1/2H, so the output of the skew detection circuit 9 is inverted and the switch SW2 is switched to the dashed line side, causing the video delayed by 1/2H. The signal is output, and as a result, the period of the horizontal comrade signal becomes uniform. When the rotary head 6a advances further and moves from the recording track t3 to t5, a skew jump occurs again, and the output of the skew detection circuit 9 is inverted and becomes the solid line side, resulting in a video signal with the period of the horizontal synchronization signal aligned. Output. In this way, skew distortion on the television screen can be prevented.

[Problems to be Solved by the Invention] The above-described skew distortion prevention device uses the delay circuit 10, but this delay circuit is expensive and has the disadvantage that the VTR becomes expensive.

This invention eliminates the use of the above-mentioned expensive delay circuit, and reduces the operating gap to (1/2), which was provided in this type of VTR.
This invention provides an inexpensive skew distortion prevention device using a rotary head that is shifted by +n)H.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a magnetic tape that rotates alternately in a direction crossing the running direction of a magnetic tape by a first rotary head or a second rotary head having mutually different azimuths. The tape is scanned to form a recording track, and the tape speed can be selected between standard speed and half speed, which is half the standard speed, and when the tape speed is at the standard speed, adjacent recording tracks are scanned. The positions of the horizontal synchronization signals of the video signals shown above are aligned, and at the half speed, the positions of the horizontal synchronization signals on every other recording track with the same azimuth are shifted by 1/2H. This VTR has the same azimuth as the above-mentioned first rotary head, and the operating gap with the first rotary head is shifted by a distance (1/2 + n) H, and the rotary head has the same azimuth. A separate second rotary head is provided, each having a track width approximately 172 times that of the first rotary head, and the second rotary head is used when recording and reproducing at half speed; Equipped with a skew detection circuit that detects the unevenness of the horizontal synchronization signal that occurs when a video signal recorded at a high speed is played back at a tape speed different from that at the time of recording, and is designed to deal with the unevenness of the horizontal synchronization signal. In a VTR, when the video signal recorded at the half-speed speed is played back at a tape speed different from that at which it was recorded, when the skew detection circuit detects an uneven horizontal synchronization signal, this unevenness occurs. In order to cope with this problem, a selection means is provided for selecting and using the first rotary head and the second rotary head described above.

[Example code] 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 above indicate the same components, so detailed explanation thereof will be omitted. ! 2a
, +2b indicate rotating heads, the position of the operating gap is shifted by (+/2+n)H with respect to the above-mentioned rotating heads 6a and 6b, and the track width is twice that for standard speed. .

13a and 13b are preamplifiers, and the rotating head +2
The reproduced outputs from a and 12b are amplified to the operating level of the subsequent circuit. SW3 and SW4 are switches which select the output video signals from the preamplifiers 7a, 13a, 7b and +3b and supply them to the switch 11 described above. 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 recording track tl in FIG. 4 is being scanned by the rotary head 6a when reproducing a video signal at a tape speed five times that of recording, the switch SR1. SW3 and SW4 are switched to the side shown by the solid line. When the rotary head 6a advances and moves from the recording track opening to t3, the period of the horizontal synchronizing signal of the reproduced video signal becomes irregular, and the skew detection circuit 9 detects a signal as shown in FIG. 6 (4).
) is obtained, which triggers the T-type flip-flop 14. As a result, the output shown in FIG. 6 (5) is obtained from the flip-flop, and the output pulse causes the switch S1.13 to
S4 is switched to the side shown by the broken line. With this switching, the video signal from the rotary head +2a instead of the rotary head 6a is supplied to the video signal processing circuit 8 via the preamplifier +2a, switches SW3, and SWI. Rotating head +2
As mentioned above, the working gap of a is (1/2 + n
) H, the irregularity in the frequency of the horizontal synchronizing signal of the reproduced video signal disappears, and the output of the skew detection circuit 9 is instantaneously reversed.
The output pulse shown in 4) has an extremely narrow pulse width.

In this way, a video signal with a uniform period of the horizontal synchronizing signal is obtained from the output terminal 11. The T-type flip-flop 14 switches SW3 and SW4 during the period from when the output of the skew detection circuit 9 is inverted to when it is next inverted.
is held in some state.

In the above embodiment, the video signal that has passed through the switches SW3 and SW4, which are switched by a T-type flip-flop, is selected by the switch SWI, but as shown in FIG. 2, the video signal is selected by the switches SW5 and SW6, which are switched by a head switching pulse. The selected video signal may be selected by a switch SW7 operated by a T-type flip-flop. Furthermore, the second
In the figure, the same reference numerals as in FIG. 1 indicate the same parts.

In the above embodiment, the present invention is applied to a VTR in which the start positions of each field of adjacent recording tracks are shifted by 1.5H and the magnetic tape is wound approximately 180° around a head drum equipped with four rotating heads. However,
The present invention is suitable for application to a VTR called VH3-C in which a magnetic tape is wound around the head drum over 270 degrees.

This VH5-C has four standard speed rotary heads arranged at 906 intervals on the head drum, and the azimuths of adjacent rotary heads are different from each other, and the track width of these rotary heads is about 172 mm. The position of the working gap is (1/2+n)l (with rotating heads for each separate half speed separated).

Although not shown in FIGS. 1, 2, and 5, a well-known rotary transformer is interposed between the rotary head and the preamplifier.

[Effects of the Invention] As described above, the present invention provides the first rotary head I2a, +2b or the second rotary spatula t"6a, 6b having mutually different azimuths in the direction intersecting the running direction of the magnetic tape 10.
The recording tracks T1 to T5 or t are scanned alternately by
It is possible to select a standard speed or a half speed which is 172 times the standard speed as the tape speed.
The positions of the horizontal synchronizing signals of the video signals on ~T5 are aligned, and at the half speed, every other recording track tl, t3 . t5 or t2. L4. t6
V where the position of the upper horizontal synchronization signal is shifted by 1/2H
. ), and the track width of the rotary head is 1/2 of the first rotary spatula F'12a, +2b.
The second rotary head is used when recording and reproducing at half speed, and the video signal recorded at half speed is In a VTR equipped with a skew detection circuit 9 for detecting uneven horizontal synchronizing signals that occur when playing back tapes at different tape speeds, the VTR is designed to deal with uneven horizontal synchronizing signals, and when the tape is recorded at half speed, When the skew detection circuit 9 detects an irregularity in the horizontal open Ill signal when reproducing the recorded video signal at a tape speed different from that at the time of recording, the first rotation described above is performed in order to cope with this irregularity. Switches SW3, SW4, SW5, which are used to select the head and the second rotary head. Since the selection means such as SW6 is provided, it is possible to provide a VTR that can prevent skew distortion without installing an expensive delay circuit as in the conventional case.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment, FIG. 3 is a schematic diagram showing recording tracks on a general magnetic tape at standard speed, and FIG. Fig. 4 is a schematic diagram showing recording tracks on a magnetic tape at 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. The time chart, FIG. 7, is a schematic front view of a rotary head block of a conventional device. 6a, 6b, ! 2a, 12b: Rotating head, 9-unit detection circuit, Sn3. SW4. 5. SW6
:switch. Singing

Claims (1)

[Claims] Recording tracks are formed by alternately scanning in a direction intersecting the running direction of the magnetic tape by a first rotary head or a second rotary head, which will be described later, having mutually different azimuths. , the tape speed can be selected from standard speed and half speed, which is half the standard speed, and when the tape speed is set to the standard speed, the position of the horizontal synchronization signal of the video signal on the adjacent recording track is They are lined up, and at the half speed, the position of the horizontal synchronization signal on every other recording track with the same azimuth is 1/2H (H).
is a distance corresponding to the interval between horizontal synchronizing signals on the recording track), the VTR has the same azimuth as the first rotary head, and the operation with the first rotary head is the same as that of the first rotary head. The gap is the distance (1
/2+n) H (n is an integer), and the track width of the rotary head is approximately 1/2 of that of the first rotary head.
2, the second rotary head is used for recording/playback at half speed, and the video signal recorded at half speed is recorded. In a VTR that is equipped with a skew detection circuit that detects uneven horizontal synchronizing signals that occur when the tape is played back at a tape speed that is different from the normal tape speed, the VTR is designed to deal with uneven horizontal synchronizing signals. When reproducing a recorded video signal at a tape speed different from that at the time of recording, when the skew detection circuit detects an irregularity in the horizontal synchronization signal, the first rotation described above is performed to deal with the irregularity. V characterized by comprising a selection means for selecting and using the head and the second rotating head.
Skew distortion prevention device in TR.