JP2725325B2 - Video signal recording and playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal recording / reproducing apparatus for intermittently recording or reproducing a video signal.

2. Description of the Related Art In recent years, video signal recording / reproducing apparatuses, especially video tape recorders (hereinafter, referred to as VTRs) are fields that have grown significantly in recent years, and their uses have been diversified. Among them, a time-lapse VTR capable of intermittent recording or reproduction is capable of recording for a long period of time from about 24 hours to about 480 hours. In addition, time-lapse VTRs based on low-cost home-use VTRs have been developed, and the market has been expanding due to price reductions. In this type of time-lapse VTR, the rotating head for recording and reproducing the video signal and the fixed erasing head for erasing the magnetic tape are separated from each other in configuration, so that it is recorded on the already recorded magnetic tape again. In this case, an unerased portion of 2 to 3 seconds always remained. This 2
〜3 seconds seems to be a short time, but it is 10-15 minutes for intermittent recording in 480 hour mode, which is not a negligible value. As a countermeasure, there has been a method in which a rotary erasing head is provided preceding a rotary head for recording and reproduction, and a portion of a track to be recorded is pre-erased by the rotary erasing head.

Problems to be Solved by the Invention However, in the above-mentioned conventional configuration, there is a problem that the rotation erasing head is required and thus the cost is high.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a time lapse VTR capable of erasing an unerased portion without adding a rotating erase head.

Means for Solving the Problems To achieve this object, a video signal recording / reproducing apparatus of the present invention performs constant bias recording on a predetermined portion of a magnetic tape in at least one field before a video signal to be intermittently recorded, and then performs Record the video signal in the same part,
Further, the level of the constant bias recording is set higher than the recording level of the video signal.

Operation With this configuration, constant bias recording is performed at a large level in a field immediately before recording in a portion where a video signal is to be recorded, so that erasing can be performed by a rotating head used for normal recording and reproduction. It is possible to realize an extremely inexpensive device, for example, it is possible to prevent overwriting on an unerased portion, and it is not necessary to provide a rotary erasing head.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of a video signal recording / reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view showing a head arrangement of the embodiment and a waveform diagram used for explaining the operation. Here, the horizontal axis of the waveform diagram in FIG.
The rotation angles θ of the rotary heads A and B shown in FIG. 6A are shown, and the waveform numbers correspond to the signals in FIG. FIG. 2A shows the rotary heads A and B provided on the rotary cylinder 19 and the rotary cylinder 1
9 shows the relationship with the magnetic tape 20 wound.

In FIG. 1, a video signal input from an input terminal 1
12 is input to the sync separation circuit 2, and the sync separation circuit 2
Separates and outputs the vertical synchronization signal 13. This synchronization signal
The rotating heads A and B rotate in synchronism with 13, and their rotation cycle is one frame. Accordingly, the rotary heads A and B can perform recording and reproduction in units of one field. In the intermittent recording, the recording is performed while the running of the magnetic tape is stopped, so that the rotary heads A and B scan the same portion of the magnetic tape. Therefore, one field is recorded on one of the rotary heads A and B, and one frame can be reproduced by the rotary heads A and B. This is for general household
This is the same as field still (still image reproduction) in a VTR.

The vertically separated vertical synchronizing signal 13 is input to a timing circuit 3, which includes an erasing pulse 14 for erasing operation (see 14 in FIG. 2B) and a recording pulse 15 for recording operation (see FIG. 2). (See b) 15) and output. The generation of these pulses is set by a known frequency dividing circuit according to the time mode of intermittent recording. Here, the erase pulse 14 is a pulse including at least one field before the field of the video signal 12 to be recorded, and the recording pulse 15 includes a period of the erase pulse 14 and one field of the video signal 12 to be recorded. It is a pulse.

The erasing pulse 14 is a switch 4 for switching between the video signal 12 and a constant DC bias signal generated by the bias generation circuit 7.
To work. Thereby, the erase pulse is applied to the FM modulator 8.
In one field period of 14, a DC bias signal is input (see 16 in FIG. 2B). Accordingly, the output 17 of the FM modulator 8 is an FM signal having a constant frequency during the period of the erase pulse (see 17 in FIG. 2). further,
The erase pulse 14 operates the gain switch 6 of the recording current amplifier circuit 5 to increase the gain during the erase pulse. The operation of each part by the erase pulse 14 determines the erase frequency and the erase current in the present invention. That is, the magnitude of the DC bias signal determines the erase frequency, and the FM signal 17 is 5M
Select a value that gives a frequency of about Hz. Further, the gain of the recording current amplifier circuit 5 during the erasing pulse is selected to be about twice the period of the video signal to be recorded (see 18 in FIG. 2B).

The recording pulse 15 controls the switch 9 that conducts the output 18 of the recording current amplifier circuit 5 to the rotating heads A and B, so that the recording current flows through the rotating heads A and B. That is, recording pulse 15
During this period, the recording signal 18 is supplied to the rotary heads A and B via the switch 9. In the example of the waveform 18 shown in FIG. 2B, a current flows through the rotary head A during a period of recording with a constant DC bias signal, and a current flows through the rotary head B during a period of recording a video signal. Of course, this relationship may be reversed. By doing so, erasure by constant bias recording can be performed by the rotary head A in the first one field, and video signals can be recorded by the rotary head B in the next one field.

Effect of the Invention As described above, the present invention employs a configuration in which erasing is performed by constant bias recording in a field before recording a video signal, and then the video signal is recorded. The practical effect is great, for example, recording can be prevented, and there is no need to add a rotary erase head, and an inexpensive device can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video signal recording / reproducing apparatus according to an embodiment of the present invention, FIG. 2A is a plan view showing a head arrangement in the apparatus of FIG. 1, and FIG. FIG. 3 timing circuit, 4 switch, 5 recording current amplifier, 6 gain switch, 7 bias generation circuit, 8 FM modulator, 9 switch, A, B ...... Rotating head.

Claims (1)

(57) [Claims] 1. A constant bias recording on a predetermined portion of a magnetic tape in at least one field before a video signal to be intermittently recorded, and then the video signal is recorded on the same portion, and a level of the constant bias recording. Is set higher than the recording level of the video signal.