JP2890417B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention records a video signal captured by a monitoring camera or the like and data related to the video signal,
The present invention relates to a magnetic recording / reproducing apparatus useful for reading at high speed.

[Summary of the Invention]

The present invention is directed to an apparatus that captures an image of an object monitored by a TV camera or the like over a long period of time, and records and reproduces the image on a VTR. Divided into
The same data is superimposed and recorded on each block, and at the time of reproduction, data is read from the video signal by a gate signal output based on the zero cross point of the reproduction RF signal of the magnetic tape. In addition, it is possible to detect data corresponding to an arbitrary shooting screen while reproducing a monitoring scene by a TV camera at high speed.

[Conventional technology]

Nuclear power plants, warehouses where important properties are stored,
Or, in a bank, etc., it is difficult for humans to constantly monitor the condition of the furnace core and the stored articles, so a television (TV) camera is usually installed in such places, and this TV
Video signals captured by the camera are recorded in a magnetic recording / reproducing device (VTR) or the like.

Then, if necessary, the magnetic tape on which the video signal photographed by the TV camera is recorded can be reproduced by the same VTR or another reproduction VTR to inspect the subject for abnormalities or theft. It has been made possible.

By the way, since a surveillance TV camera generally has an object whose change in the subject is extremely small is symmetrical, for example, a frame feed shooting mode in which a video signal for one frame is recorded for one minute or five minutes is adopted. Thus, the subject image is recorded on one magnetic tape for a long time.

Therefore, it is difficult to keep track of time when reproducing such a magnetic tape at normal speed.
Also, it is difficult to detect when the subject has changed.

Therefore, when recording a video signal captured by a TV camera, data of the recording time of the video signal and various data (room temperature, brightness, etc.) during the recording time are simultaneously recorded by a time code. .

[Problems to be solved by the invention]

However, it is difficult to record such data in the longitudinal direction of the magnetic tape when the magnetic tape travels by a frame feed. Even when recorded on a recorded magnetic tape, there is a problem that it is extremely difficult to detect the photographed image in a fast-forward or reverse mode.

[Means for solving the problem]

The present invention has been made in view of such a problem. For example, a video track in which a video signal captured by a surveillance TV camera is recorded is divided into a plurality of blocks, and each block is subjected to frequency modulation (FSK). ), The same data is superimposed and recorded, and when this magnetic tape is reproduced by fast-forward or rewind operation, first,
A 0 cross area of the reproduction RF signal is detected, and a wind gate that activates a data detection circuit is driven for a predetermined time by a signal detected from the 0 cross area. From the reproduction RF signal passing through the wind gate, The data can be read out.

[Action]

Since the same data is continuously distributed and recorded in a plurality of blocks on the video track where the video signal is recorded, the magnetic head crosses the video track even during fast-forward or rewind playback. When you can detect the data. Therefore, after capturing the situation at the time of an accident or the occurrence of an unusual situation in nature observation, etc. with a monitoring TV camera, the data at that time is detected while performing fast-forward playback of the recording magnetic tape. The situation at that time can be output as a reproduced image.

〔Example〕

FIG. 1 (a) shows an outline of a recording system of a magnetic recording / reproducing apparatus of the present invention, and FIG. 1 (b) is a block diagram showing a circuit system for reading data from a recorded magnetic tape. In this embodiment, an 8 mm VTR is symmetrical.

First, data recording will be described with reference to FIG. 1A. Reference numeral 1 denotes an FM modulator for modulating a luminance signal supplied from a monitoring TV (not shown), and reference numeral 2 denotes a cutoff frequency of, for example, 3 MHz. It is a low-pass filter.

No. 3 is an ATF (Automatic T) that is superimposed and added together with a video signal to each recording track so that a tracking error of an 8 mm magnetic tape can be detected during reproduction.
Racking Finding) signal generation circuit, and this ATF signal has four frequencies f ₁ shown in the frequency allocation of FIG.
It is formed from the signals of ~f _4. As is well known, the 4 signals of frequency f ₁ ~f ₄ are recorded superimposed with the luminance signal to the recording track in a predetermined order through the low-pass filter 4, the ATF signal during reproduction The rotation head can be tracked by detecting the rotation.

Reference numeral 5 denotes a data generation circuit for generating a time code or a frame code added to the video signal being monitored. This data generation circuit digitizes the temperature at the monitoring point via a sensor, Can be output in parallel with the data.

The data of the data generation circuit 5 is a signal processing circuit 6 which performs signal processing such as addition of a CRC code and parallel-to-serial conversion.
, And is converted to a signal in the frequency domain of F _{1 to} F ₂ by the band allocation filter 8 and output to the adder circuit 9 through the band pass filter 8, for example.

The adder 9 superimposes the video signal (Y signal), the ATF signal, and the data and outputs the superimposed data to the recording amplifier 10.

As shown in FIG. 3, the FM data recorded on the video track includes, for example, 50 bytes of data as one unit block data BD, and each track T, T,. Individual block data BD ₁ , BD ₂ , BD ₃ ‥‥‥
Distributed and recorded repeatedly.

The signal of the magnetic tape recorded by such a recording system is detected via the reproducing head H _R and the reproducing amplifier 20 as shown in FIG.

The reproduction signal output of the reproduction amplifier 20 is supplied to the low-pass filter 21.
(F _C = 3MH _Z) by the luminance signal is demodulated by the demodulator 24 is extracted. Moreover, ATF signal is extracted by a low-pass filter 22 which cutoff frequency is the 500KH _Z, ATF servo circuit 25
Supplied to

Further, a data reproduction signal is extracted by a band-pass filter (center frequency F _{1 to} F ₂ ), and the FM data demodulation circuit
The data supplied to 26 and demodulated is input to the data processing circuit 30.

On the other hand, the envelope of the reproduced RF signal component of the reproducing amplifier 20 is detected by the RF signal processing circuit 31 as described later, and the zero cross point of the envelope signal is detected.
Then, a gate pulse (window pulse) generating circuit 32 for outputting a gate pulse at a predetermined position with reference to the detection position of the zero cross point is started, and its signal is a wind gate pulse of the data processing circuit 30 or an enable signal. Supplied as

FIG. 4 shows a recording format of a magnetic tape recorded by the recording system of FIG. 1 (a). A video signal of a monitoring place taken by a TV camera every 1 to 5 minutes is a normal signal. helical scan VTR and at the same time is recorded on each track T ₁ through T _n as a video signal for one field in the same manner, data output from the data signal generation circuit 5 is distributed to 200 blocks B within one track Are superimposed and recorded with the same data.

When such a magnetic tape is played back at a normal playback speed, the playback head scans almost each track using the ATF signal as tracking information, and is superimposed on each track at the same time as the playback video signal for one frame that has been framed. The recorded data can also be detected.

However, when the magnetic tape is reproduced in the fast-forward mode (cue review), the trajectory of the reproducing head crosses each track as shown by the dashed line in FIG. 4, and the reproduced RF signal at that time is shown in FIG. As shown in the figure, the level changes every time the track passes between tracks.

Magnetic recording and reproducing apparatus of the present invention, an envelope of the reproduced RF signal obtained by such a fast-forward reproduction mode is detected in the RF signal processing circuit 31, 0 cross pulse P which rises at the 0 cross point t ₀ as shown in Figure 5 Outputs ₁ . Then, and outputs a window gate pulse P ₂ to provide the 0 cross pulse P ₁ then the gate pulse generating circuit (monostable multivibrator) 32.

Serial data of the data demodulated in the data processing circuit 30
S-P conversion circuit 30A for performing parallel conversion is driven to enable state by the window gate pulse P _2.

Therefore, in the fast-forward playback mode, the data contained in the RF signal in the hatched portion in FIG. 5 is supplied to the next error correction 30B, where the error is corrected and then output.

In this case, since the data recorded in one track is distributed as the same data to, for example, 200 blocks, even when performing fast forward reproduction at several tens times speed,
Data recorded within a predetermined range from the zero cross point of the reproduced RF signal can be sampled with high accuracy by the gate pulse.

In other words, even during fast-forward playback, the reproduction of data contaminated by noise can be eliminated, so that the reliability of the reproduced data is increased.

As shown by the two-dot chain line in the replay reproduction (REV), the head also crosses the video track at the time of the variable speed reproduction crossing the track. Even in this case, the reproduction RF shown in FIG. It is needless to say that the data superimposed on each track can be reproduced with high accuracy by the gate pulse based on the signal.

〔The invention's effect〕

As described above, the magnetic recording and reproducing apparatus of the present invention
A video track formed in an oblique direction is divided into a plurality of blocks, and the same frequency-modulated data is superimposed and recorded on each of the divided blocks for each track. Since the data recorded on the video track can be read at the timing based on the cross point, it is superimposed on the video signal when monitoring the recorded video signal in fast-forward or rewind playback mode. There is an effect that the stored data can be accurately read.

[Brief description of the drawings]

1 (a) and 1 (b) are block diagrams of a recording / reproducing system of a magnetic recording / reproducing apparatus of the present invention, FIG. 2 is a diagram showing a frequency spectrum of a recording signal, and FIG. 3 is recorded in a track. FIG. 4 is an explanatory diagram of block data, FIG. 4 is an explanatory diagram showing a locus of a head during variable speed reproduction, and FIG. 5 is a gate pulse waveform diagram for extracting recorded data. In the figure, 20 is a reproducing amplifier, 30 is a data processing circuit, and 31 is a reproducing amplifier.
RF signal processing circuit, 32 is a gate pulse (window pulse)
2 shows a generating circuit.

Claims (1)

(57) [Claims] 1. A magnetic recording / reproducing apparatus which sequentially records tracks inclined in an oblique direction of a magnetic tape, wherein each track is divided into a plurality of blocks, and a frequency of a video signal is modulated for each block. Superimposing means for superimposing the same data; recording means for recording the output of the superimposing means on the magnetic tape; reproducing means for reproducing a signal recorded on the magnetic tape and outputting a reproduced signal; Zero cross point detecting means for detecting the zero cross point of the magnetic tape, and at least when the magnetic tape is reproduced at a high speed, the gate signal at a timing based on the timing at which the zero cross point detecting means detects the zero cross point of the reproduced signal. And a data detection unit for detecting data from the reproduction signal based on the gate signal. Magnetic recording and reproducing apparatus characterized.