JPS6322714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses two rotating magnetic heads having different azimuth angles to record one field of video signal on a single tape tilted with respect to the longitudinal direction of the magnetic tape. This invention relates to a helical scan type magnetic recording/reproducing device (VTR) that sequentially records and reproduces video signals so as to form a trajectory. this kind of
An example of a VTR is a VHS system VTR. this
A VHS system VTR is generally configured to be able to select between a 2-hour mode (track pitch of 58 .mu.m) and a 6-hour mode (track pitch of about 19 .mu.m) by changing the tape speed.

In both modes, during playback, a high-speed playback image is played back at a tape speed faster than the tape speed during recording, a low-speed playback image is played back at a tape speed slower than the tape speed during recording, and one field is played back when the magnetic tape is stopped. In order to obtain good field still images from which video signals are continuously obtained, it is conceivable to provide a total of four heads, a pair of heads dedicated to the 2-hour mode and a pair of heads dedicated to the 6-hour mode.

In FIG. 1, R and L are a pair of magnetic heads for the 6-hour mode, and R' and L' are a pair of magnetic heads for the 2-hour mode. L is 35μm, R′ is 32μm, L′ is
It is 45μm.

The distances between the magnetic heads R and L' and between the magnetic heads R' and L are set on the same plane so as to correspond to the recording locus length (370 μm) of one horizontal scanning period on the magnetic tape. In other words, when recording and playing back in 2-hour mode,
During recording and reproducing in the 6-hour mode, the R' and L' magnetic head pairs are used to perform recording and reproducing.

When using such a magnetic head, you can achieve relatively good high-speed playback and playback in time mode.
Although low-speed playback and field still images can be obtained, problems occur during high-speed playback in 2-hour mode recording and playback.

That is, in the 2-hour mode, since the track pitch is 58 .mu.m and the head widths are narrow at 32 .mu.m and 45 .mu.m, more than half of the reproduced image becomes noise during high-speed reproduction, making it impossible to obtain a good high-speed reproduction image.

Figure 2a shows the relationship between the recording trajectory and head scanning trajectory in the high-speed fast-forward playback mode at 5x speed, where R' and L' are the recording trajectory by heads R' and L', respectively, and 1 is the head scanning trajectory. This is the scanning trajectory of R′.
The reproduction signal of head R' at this time is shown in Figure 2b.
It becomes an envelope signal as shown as R′,
Many signal deletion areas occur.

At this time, the reproduced signal of another set of opposite azimuth heads L adjacent to head R' becomes an envelope shown by L in FIG. One embodiment of this configuration is shown in FIG.

In FIG. 3, 2 indicates the aforementioned heads R and L,
It is a head cylinder with R' and L'6,7,
Reference numerals 8 and 9 indicate head amplifiers for the heads L, R, L', and R', respectively, and the head amplifiers 6, 7,
8 and 9 are configured to be electrically connected alternately every half rotation of the cylinder 2. The outputs of head amplifiers 6 and 7 are transferred to head amplifier 8 by a mixing circuit 11.
and 9 are mixed by a mixing circuit 12 and guided to contacts a and b of a changeover switch 13, respectively.

14 and 15 are the mixing circuits 11 and 12;
The outputs of the detection circuits 14 and 15 are compared in level by a comparison circuit 16, and the output is sent to the detection circuit 14 via a switch 18 that is closed during high-speed reproduction. When the output level is high, the changeover switch 13 is driven to the a contact, and when the output level of the detection circuit 15 is high, the changeover switch 13 is driven to the b contact.

That is, the output terminal 17, which is the output of the changeover switch 13, is configured to selectively receive a higher level reproduction signal from the heads R' and L, and R and L' having different azimuth angles. has been done.

According to the above configuration, a good high-speed reproduction image can be obtained even in the 2-hour mode, but a problem occurs when transitioning from the high-speed reproduction state to the normal reproduction state.
When transitioning from high-speed playback to normal playback, the speed of the magnetic tape changes sequentially, so the relative speed between the magnetic tape and the rotating head changes, and as shown in Figure 2a during high-speed playback, the speed of the magnetic tape changes. The scanning locus does not form a constant angle.

Therefore, when transitioning from the high-speed playback state to the normal playback state, the switch 18 shown in FIG. 3 is disconnected.
If the switching operation of the changeover switch 13 is stopped (the changeover switch 13 is fixed at contact b), a good reproduced image cannot be obtained with heads R' and L' alone in this transient state.

The present invention is configured so that a good reproduced image can be obtained even in this transient state, and even when switching from the high-speed reproduction state to the normal reproduction state, the high-speed reproduction state remains until the magnetic tape returns to the normal reproduction state. Similarly, the changeover switch 13 is to be driven.

One embodiment is shown in FIG.

The difference between FIG. 4 and FIG. 3 is that the switch 19, which is closed during high-speed recording and reproduction in the 6-hour mode, is connected to a delay circuit 20, and the output of the delay circuit 20 closes the switch 18. At the point.

The delay circuit 20 immediately generates an output when the switch 19 is pressed and voltage is applied;
When the switch 19 is opened, the output is reduced after a delay corresponding to the time required for the magnetic tape to shift from the high-speed playback state to the normal playback state. For example, as shown in FIG. The control signal (FIG. 6a) applied by the switch 19 during the high-speed reproduction state is differentiated by the differentiating circuit 21,
The output corresponding to the falling edge drives the monostable multivibrator 22, and its output (Fig. 6b)
may be mixed with the control signal a to form the signal c for driving the switch 18.

Then, the delay time t of the monostable multivibrator 22 may be set to be longer than the time required to shift from the high-speed reproduction state to the normal reproduction state.

It should be noted that when transitioning from the high-speed reproduction state to the normal reproduction state, the vertical synchronization signal may be omitted because the relationship between the head scanning locus during reproduction and the recording locus does not match as described above. To correct this missing vertical synchronization signal, as shown in Figure 7, a monostable multivibrator is used to create a pseudo vertical synchronization signal b delayed by a fixed time T _A from the head switching pulse a. It is sufficient to replace this pseudo vertical synchronizing signal b with the vertical synchronizing signal in the reproduced signal for only the transition period t time shown in FIG. 6b.

As described above, according to the present invention, a good reproduced image can be obtained even when transitioning from high-speed reproduction to normal reproduction.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an example of the arrangement of the rotary head used in the present invention, Fig. 2a is a diagram showing the relationship between the recording trajectory and the reproduction trajectory during high-speed reproduction, and Fig. 2b shows the reproduction signal envelope. 3 is a block diagram showing the configuration of the pre-stage of the present invention, FIG. 4 is a block diagram showing one embodiment of the present invention, FIG. 5 is a block diagram of the main part, and FIG. 6 is the same main part. FIG. 7 is a waveform diagram illustrating the operation of the means for correcting the deletion of the vertical synchronizing signal. 2... Rotating cylinder, 6, 7, 8, 9... Head amplifier, 11, 12... Mixing circuit, 13
...Selector switch, 14, 15...Detection circuit, 1
6... Comparison circuit, 18, 19... Switch, 20
...Delay circuit.

Claims (1)

[Claims] 1. Two magnetic head pairs each consisting of two magnetic heads having different azimuth angles, each pair of magnetic heads having an index angle of approximately 180° to each other,
The magnetic heads between the different pairs of magnetic heads are arranged on a rotating cylinder on the same plane so that the magnetic heads having different azimuth angles are close to each other, and the magnetic tape is wound along the rotation locus of the magnetic heads.
The magnetic tape is run while being selectively switched to two tape speeds, and the above-mentioned two speeds are set according to the tape speed.
One of the two magnetic head pairs is selected, the two magnetic heads of the selected magnetic head pair are sequentially switched to sequentially record video signals, and during playback the tape speed is made faster than the recording speed to produce high-speed playback images. The four magnetic heads are used for the high-speed image playback state in which the tape speed is obtained, and the transition state from the high-speed image playback state to the normal playback state where the tape speed is equal to the tape speed at the time of recording. A rotary head type magnetic recording and reproducing apparatus characterized in that the reproduction signal envelopes are compared and the output of the magnetic head with the larger envelope is selected as the output signal.