JPS5935548B2 - magnetic recording and reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helicalskian type magnetic recording/reproducing device, and is intended to facilitate program editing.

Conventionally, in a helical scan type magnetic recording/reproducing apparatus, when it is desired to record a different signal at a certain point in time while reproducing a magnetic tape, it has been difficult to erase old signals after that point in time.

That is, in the helical scanning method, since the video track is inclined with respect to the tape width direction, there remain portions that cannot be erased by a full-width erase head that erases uniformly in the tape width direction. As a result, beads and noise were extremely increased at the joint between the old signal and the new signal, degrading the image quality. Therefore, in addition to two rotary heads for recording and reproducing video signals, one rotary head for erasing is provided, and a means for erasing video tracks one by one has been devised. However, in this case, it is necessary to provide one rotary erasing head, and it is also necessary to provide dedicated wiring for passing the erasing current to the erasing rotary head through a slip ring or a rotary transformer. As described above, it was difficult for helical scan type video tape recorders to successfully connect old signals and new signals. The present invention attempts to successfully connect old signals and new signals in a field-skip helical scan video tape recorder.
Here, the field skip method is a method in which every other field is recorded during recording, the same track is played back twice during playback, and unrecorded fields are replaced with the previous field. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a magnetic tape pattern showing one embodiment of the present invention.

1 is a magnetic tape that runs in the direction of arrow 2.

In FIG. 1, the magnetization patterns of video tracks such as 6 and 7 are drawn upward to the right, but the idea of the present invention can be similarly applied to magnetization patterns upward to the left. Furthermore, in FIG. 1, the audio track and control track are omitted. Assume now that a video signal A has been recorded on the magnetic tape 1.

The solid line video track indicated by 3 indicates the recorded track of the video signal A.

Suppose that when the playback head reaches point P on the video track 6 while playing back the video signal A, it is desired to erase the subsequent video signal A and record another video signal B. Here, the head that plays the same track first is called the first head, and the head that plays it after that is called the second head. If the head at point P is the first head, then the first head plays the remaining part on the video track 6, and then when the second head finishes playing the video track 6, the video signal Assume that the recording state B is entered. If the head at point P is the second head, then when the second head has finished playing the remaining portion on video track 6, video signal B
shall enter the recording state. FIG. 2 is an example of a circuit system for implementing the present invention. In FIG. 2, components that are not directly connected to the present invention, such as a rotary transformer or a slip ring, are omitted. In the reproducing state, the signal regenerated by the first head 8 is transmitted to the relay switch 14.
The signal passes through the head amplifier 9 and enters the head amplifier 9. Terminal 12 is then connected to a regeneration circuit. Similarly, the signal reproduced by the second head 15 passes through the relay switch 22 and the head amplifier 16, and enters the reproduction circuit from the terminal 19. As mentioned earlier, when video signal A is being played back and video signal B is to be recorded, information such as a recording command signal such as a rising pulse or rising NRZ (now return to zero) is input to the terminal 27. . This information is self-held by the control signal generation circuit 26. A pulse train from the PG coil is input from the terminal 25. Here, the PG coil is used to detect the rotational speed of the rotating head in order to apply servo to the rotating head, and a pulse train of one frame period can be obtained. This pulse train is appropriately delayed by a pulse delay circuit 24 and sent to 26. In this case, the delay width of the pulse delay circuit 24 is determined so that a pulse is generated when the first head 8 reaches the starting point Q of the video track 7. Normally, the signal generated by the PG coil is the result of differentiating a positive pulse train with a period of 1 frame, but at terminal 25, the signal is 1
Leave it in the state of a positive pulse train with a frame period. Further, when the pulse train at the terminal 25 coincides with the point at which the first head 8 starts writing, no pulse delay circuit is necessary. The control signal generation circuit 26 is a circuit that outputs a pulse when a pulse is input from the pulse delay circuit 24 while holding the signal 27 by itself. The self-holding state of the control signal generating circuit 26 is released by a signal from the terminal 28. The pulse output from the control signal generation circuit 26 enters the power supply circuit 11, where it is self-maintained and supplies power to the relay solenoid 13 and the erase current generation circuit 10. Therefore, the relay switch 14 enters the erase state, and the erase current from the erase current generating circuit 10 is supplied to the first head 8. The erase current is alternating current. The dash-dotted line 5 in FIG. 1 is the position of the gap centerline of a fixed full width erase head. Since the area to the left of this one-dot chain line 5 is erased by the full-width erase head, it is not necessary to erase by the first head 8. Therefore, in order to put the first head 8 into the erased state, the pulse output from the circuit 26 is delayed by an appropriate amount of time in the pulse delay circuit 23, and the delayed pulse is input into the circuit 11.
When the self-holding state of the first head 8 is released and the output of the circuit 11 is set to O, the first head 8 enters the reproducing state. Incidentally, the first head may be set to the erase state without being set to the playback state, and the first head may perform another erase in addition to the full width erase. Figure 3 is an enlarged view of video tracks 6 and 7 in Figure 1.

The moment the first head 8 enters the erase state, that is, the first
When the first head 8 is at the starting point Q of the video track 7, the second head is also at a point R on the video track 6, near the end point S of the video rack 6. This occurs because the magnetic tape 1 is wound around the head drum for more than one field, and the time from point R to point S is usually within 15 horizontal scanning times, or about 1 msec. If this is called an overlap time, the second head 15 must enter the recording state after the overlap time from when the first head 8 enters the erase state. Further, the time it takes for the second head 15 to move from point R to Q is one field time. One field time is approximately 16.6 msec in the NTSC system.
In the PAI method and the SECAM method, it is 20 msec.

After all, the time at which the second head 15 enters the recording state is the same as that at the first head 15.
The time required for the head 8 to enter the erase state must be delayed by at least 1 msec and at most one field time.
The pulse delay circuit 29 fulfills this role. A specific example of the pulse delay circuit 29 is shown in FIG. 4, and waveforms of each part are shown in FIG. 5. The output pulse 39 of the circuit 26 enters the input terminal 31 of the pulse delay circuit. 32 is an emitter-coupled monostable multivibrator, and the waveform at its output terminal 33 is as shown in 40.

If this is differentiated by capacitor 34 and resistor 35, terminal 36
The waveform of is as shown in 41. Next, if the positive pulse is removed by the diode 37, the output terminal 3 of the pulse delay circuit 29
The waveform at 8 is as shown in 42. Therefore, the pulse delay circuit 29 has a time T. The pulse 39 from the circuit 26 inputted to the circuit 26 reaches the time T after a delay time τ. +τ is output as a pulse 42. This pulse 42 enters the power supply circuit 18, which enters a self-holding state and supplies power to the relay solenoid 21 and recording amplifier 17. Therefore, the switch 22 of the relay enters the recording state and the video signal BO)F coming in from the terminal 20.
The M wave flows through the recording amplifier 17 to the second head 15. The self-holding state of the circuit 18 is the same as that of the circuit 26.
It is released by a signal from 8. When it is desired to stop recording the video signal B, a signal is input to the terminal 28. Here, the synchronization signal of the video tape recorder of the present invention and the video signal B
synchronize with the synchronization signal of the video tape recorder that sends out the signal.

As shown in FIG. 2, if the pulse 42 outputted from the pulse delay circuit 29 is passed through the terminal 30 and the control signal is also brought into the recording state in order to put the second head 15 into the recording state, the video signal A1 video signal The control signal becomes continuous through B. As described above, the present invention includes a first head that reproduces a track first, and a second head that reproduces the same track after the first head reproduces the track. This second head records every other field.
The second head is used as an erasing head for at least a certain period after recording is started with the second head, and the video signal can be connected well without providing a special erasing head. It is something that can be done. Also, by using the full-width erase head native to the device, the first head only needs to be erased for a short period of time.

Furthermore, if the first head is put into the erasing state before the second head goes into the recording state, the video signals can be connected even more precisely.

[Brief explanation of drawings]

FIG. 1 is a plan view of a tape for explaining the magnetic recording/reproducing apparatus of the present invention, FIG. 2 is a block diagram of the magnetic recording/reproducing apparatus in an embodiment of the present invention, and FIG. 3 is an enlarged view of a portion of the tape. A plan view, Fig. 4 is a circuit diagram of a part of the device, and Fig. 5 is a circuit diagram of a part of the device.
Figures A, b, c, and d are waveform diagrams for explaining the circuit. 8...First head, 15...Second head, 14,22...Switch switch, 9,1
6... Head up, 10... Erase current generation circuit, 11, 18... Power supply circuit, 2
6... Control signal generation circuit, 27... Recording command signal input terminal, 25... Pulse train human power terminal, 17... Recording amplifier, 23, 29. ...
...Delay circuit.

Claims (1)

[Scope of Claims] A first head that reproduces one track first, and a second head that reproduces the same track after the first head reproduces the track, and when recording, the second head reproduces the same track.
A magnetic recording/reproducing apparatus characterized in that the first head records every other field, and the first head is used as an erasing head for at least a certain period after the second head starts recording. 2. After starting recording with the second head, the first head is used as an erasing head until a portion erased by a separately provided full-width erasing head is reached. The magnetic recording/reproducing device according to item 1. 3 Before the second head enters the recording state, the first head
3. The magnetic recording and reproducing apparatus according to claim 1, wherein the head of the magnetic recording apparatus is placed in an erasing state. 4. A pulse train with a period of one frame adjusted so that a pulse exists when the first head reaches the starting point of a video track is added to a control signal generation circuit, and a recording command signal is added to this control signal generation circuit. , The magnetic recording device according to claim 1, wherein the pulse train after the recording command signal is outputted from the control signal generation circuit, and the first head is switched to the erasing state by this output. playback device. 5. Magnetic recording and reproducing according to claim 4, characterized in that the output of the control signal generation circuit is delayed for a certain period of time, and the delayed output returns the erasing state of the first head to the reproducing state. Device. 6 Delaying the output of the control signal generation circuit for a certain period of time,
5. The magnetic recording and reproducing apparatus according to claim 4, wherein said second head is brought into a recording state by this delayed output.