JPS6311837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In a helical scan type VTR equipped with a capstan servo device, the present invention enables switching of the rotary head to the recording and playback system at the start and end of editing using a magnetic tape non-contact method. The present invention relates to a new VTR editing device which takes into consideration the possibility of synchronization disturbance or noise mixing occurring at the beginning and end of an editing portion during playback by configuring the editing to be performed in a section.

In a so-called helical scan VTR, an electronic editing method is used when a new recording signal is inserted in the middle of a program recorded on a magnetic tape. There are various electronic editing methods, but in general, there is a playback state first.
Tracking is performed using the so-called capstan servo method, in which the rotating head of a VTR is rotated in synchronization with the frequency and phase of the synchronizing signal of the video signal to be recorded, and the tape speed is controlled by the reproduced control signal. Then, a new signal is written and inserted after the previously erased recorded track.

In this case, a rotary erase head is provided in addition to a fixed full-width erase head, and the previously recorded tracks are erased one by one by the rotary erase head during editing. continues well. Furthermore, a combination of a blanking switcher method is often used to time the editing so that video connections are made at the end of the blanking period at the end of each frame at the start or end of editing.

However, this type of editing apparatus still has the disadvantage that switching noise of the rotating video head during cut-in, where editing begins, and cut-out, where editing ends, causes synchronization disturbances or partial deterioration of image quality.

The present invention solves the problems of the conventional VTR editing device. The details will be explained below with reference to drawings showing one embodiment.

Figure 1 shows the relationship between the magnetic tape around the guide cylinder that guides the magnetic tape, the rotating head, and the full-width erasing head.Figure 1 is the guide cylinder, H1 and H2 are the rotating heads for both recording and playback, and PG.
1, PG2 is a pulse generator for generating a switching pulse for switching the rotary head output at its overlap portions a and b, PG3 is a pulse generator for capstan servo, 2 is a tape, 3,3 1 is a tape guide, H3 and H4 are rotary erasing heads provided in advance of the corresponding rotary heads H1 and H2 in the direction of rotation thereof, and 4 is a fixed full-width erasing head that precedes the rotary heads H1 and H2. Reference is now made to FIG. 2, which represents one revolution of the rotary head. If the switching positions of rotary erase heads H3, H4 and rotary heads H1, H2 are selected between a and b at the beginning and end of editing, both heads will switch to tape 2.
During playback, noise occurs on the screen, which is undesirable. Therefore, among the range b→a where the tape 2 and each of the heads H1 to H4 do not come into contact, the optimum switching range is between c→d, which has the overlap width e, the safety width f, and the switching relay operation width g.

In order to set the switching of the rotary head to the recording/reproducing system within the above-mentioned optimal switching range, and to solve the problem of the blank area based on the distance between the full width erasing head 4 and the recording start ends of the rotary heads H1 and H2. The VTR editing apparatus of the present invention is constructed as shown in FIG.

In Figure 3, 5 is an AGC circuit, 6 is a pre-emphasis circuit, 7 is a low-pass filter, 8 is a clamp, clip circuit, 9 is an FM modulator, 10, 11
indicates a recording amplifier, and the output of each amplifier is supplied to the corresponding rotary head H1, H2 via a high-speed operating relay such as a micro reed relay (described later).
In addition, 12 is a preamplifier that also serves as a switcher, 1
3 is video amplifier, 14 is limiter, 15 is FM
A demodulator, 16 is a low-pass filter, 17 is a de-emphasis circuit, and 18 is a video amplifier, which outputs the signals from the rotary heads H1 and H2, or the monitor signal from the recording system, through a recording/playback switch. The signal is received via the , and is demodulated and played back. 19 is a switching pulse generator that can be triggered by the outputs of pulse generators PG1 and PG2; 20 is a normal
Pulse generator PG that generates a detection pulse when the second rotating head H2 comes to position a, similar to a VTR.
A pulse amplifier receives pulses No. 3 and provides its output to a servo system (not shown).

Figure 30 shows an editing switching circuit which is the most important aspect of the present invention, and includes two series of first and second editing/recording switching circuits 31 and 32 associated with each recording/reproducing rotary head, and a full-width switching circuit at the end of editing/recording. An editing end signal generating circuit 33 for preventing the erasing head 4 from producing an unrecorded blank area in the erasing area; and an erasing control circuit 34 for temporarily cutting off the supply of erasing current to the full width erasing head 4 at the same time as editing is completed. Consists of.

The first editing/recording switching circuit 31 switches the first rotary head H1 to the recording amplifier 1 in the section shown in FIG.
1 in the circuit for connecting the pulse generator PG
The first unit is triggered by the output of the pulse amplifier 20 that amplifies the output of 3, and has a quasi-stable period during which the first rotary head H1, which runs at a speed of 30 rpm, travels through a section corresponding to FIG. 2b. When the stable multi-vibrator 41 and the editing switch ED1 are switched to the ON side, the power is turned on when the recording/playback switch S3, which is linked to the manually switched recording monitor/playback switch 36, is switched to the recording side R. a first gate circuit 51 that is energized and opens;
The output of the first monostable multivibrator 41 that has passed through the gate circuit triggers the first
The load is the second monostable multivibrator 42 and the first micro reed relay L1, whose metastable period is long enough to fully operate the micro reed relay, and the edit changeover switch ED2 is switched to the ON side. When the second switching transistor Tr2 conducts with the output of the second monostable multivibrator 42 as a base input and the edit changeover switch ED2 is switched to the OFF position, the output of the second monostable multivibrator 42 is turned off. The first switching transistor Tr1 is connected in series.

Similarly, the second editing/recording switching circuit 32 is triggered by the output of the pulse amplifier 20 to determine the timing at which the second rotary head H2 indexes a point during a half-rotation period in which it is not in contact with the magnetic tape. Third and fourth monostable multivibrators 43 and 44, each having a metastable period of 1/60 seconds to generate a pulse output and a metastable period during which the head H2 travels in the bc section at a speed of 30 rpm; Said first
Similar to the gate circuit 51, the edit changeover switch
With ED1 being switched to the ON side, the second gate circuit 52 is energized and opened when the recording/reproducing switch S3, which is manually switched at the desired editing recording time, is switched to the recording side R; said second monostable multivibrator 42 triggered by the output
The editing switch ED is switched to the ON side, with the load being the fifth monostable multivibrator 45 and the second micro reed relay L2, which perform almost the same function as
The fourth switching transistor Tr4 is turned on by the output of the fifth monostable multivibrator 45 supplied through the switch Tr3, and the switch ED3 is turned off.
, the third monostable multivibrator 45 is turned off by the output of the fifth monostable multivibrator 45.
It is composed of a series connection of switching transistors Tr3.

Each of the micro reed relays L1, L2 has at least self-holding contacts S6, S7, and switching contacts S10, S11 for supplying erasing current to the recording/reproducing switch S8, S9 of each rotating head and the rotating erasing head H3, H4. The micro reed relay L1 further includes a recording/reproducing switch S12 that controls power supply to an oscillation circuit 39 that supplies erasing current to the full width erasing head 4.

The second and fourth switching transistors Tr
2. The impedance between the collector and emitter of Tr4 is always switched to the OFF position in the non-editing state, and is in the edit-off state, and is short-circuited by editing switches ED6 and ED7, which are switched in conjunction with each other. Therefore, the micro reed relay L1,
L2 is in a state where it can be controlled by manual recording/reproducing switches S1 and S2.

The editing end signal generation circuit 33 includes a capacitor 3 that is charged on the ON side of the editing changeover switch ED4.
5, a time constant circuit composed of a resistor 38 that discharges the charge of the capacitor on the OFF side, and a Schmitt circuit 48 that operates upon detecting that the voltage between the terminals of the capacitor 35 has fallen below a certain level. The sixth monostable multivibrator 46 uses the output as a trigger input to set a quasi-monostable period of one frame or more, and the edit changeover switch ED1 switches the output of the sixth monostable multivibrator 46 to the OFF state. A connection 53 is applied to the control input terminals of the first and second gate circuits 51 and 52 through the gate.

The erase control circuit 34 also includes a capacitor 54 and a resistor 55 that form a discharge time constant circuit when the edit changeover switch ED5 is switched to the OFF side.
detecting a decrease in the terminal voltage of the capacitor 54;
A Schmitt circuit 56 that drives the switching transistor Tr5 and a switch S1 that is connected to the collector of the switching transistor TR5 and controls the supply of erase current to the full width erase head 4.
When the edit changeover switch ED5 is turned OFF, the full width erase head 4 is
Cut off the supply of erase current to.

Next, a description will be given with reference to the operating waveforms shown in FIG.

For editing, first, each recording/playback switch is set to the playback side P to enter the VTR playback state, and the editing switches ED1 to ED7 are turned on in conjunction with each other.
Almost instantaneously, due to the action of the capstan servo, the reproduced video signal and the video signal to be edited and recorded next become synchronized.

Next, when the start of editing recording is selected, the recording/reproducing switch S1, S2, and S3 are operated in conjunction with the recording side R.
When switched to, the first and second gate circuits 51,
52 is supplied with a voltage (power supply voltage +B) as shown in FIG. 4D to open each gate. Therefore, the output of the first monostable multivibrator 41 (FIG. 4C), which is triggered by the output of the pulse amplifier 20 that shapes and amplifies the output of the pulse generator PG3 (FIG. 4B), remains unchanged (FIG. 4C). Figure 4 E) Above 2nd
The monostable multivibrator 42 is triggered, and its output (see FIG. 4) makes the second switching transistor Tr2 conductive and energizes the first micro reed relay L1. The relay is immediately self-holding by the self-holding switch S6.

At the same time, the first rotating video head H1, which is switched by the switch S8 of the relay L1, is switched from the reproduction connection to the recording connection during the period c→d of the cylinder 1, which is not in contact with the magnetic tape, and rotates at the same time (see Fig. 4, G). An erase current is also supplied to the erase head H3.

Note that the other micro reed relay L2 is similarly energized by the output of the fifth monostable multivibrator 45 triggered by the output of the second gate circuit 52. As mentioned above, the third monostable multivibrator 43 is set to have a metastable period of 1/60 second, and the fourth monostable multivibrator 44 is set to have a metastable period that is sufficient for the head H2 to travel through the section. The output of monostable multivibrator 45 is
During the CD period, the micro reed relay L2 is energized, and the fourth transistor Tr4 is energized as a pulse sufficient for self-holding.

As a result, the rotating video head H2 always switches from playback to recording and starts editing and recording during the tape non-contact interval 1/60 second after the former rotating video head H1, but the operation waveform corresponding to FIG. I'~
They are shown correspondingly as shown in Figure 1, and their explanations are omitted.

Next, when editing is completed, each editing switch ED1 to ED7 is switched to the OFF position, and each gate circuit and monostable multivibrator are activated so that a pulse is delivered between c and d of cylinder 1.

Hereinafter, a more detailed explanation will be given with reference to the operating waveforms shown in FIG.

At the end of editing, when the editing changeover switch ED4 is switched to the OFF side, the charge in the capacitor 35 is discharged via the resistor 38. The above Schmitt circuit 48
The detection level of the capacitor 35 is determined by discharging the electric charge via the resistor 38 during at least the time equivalent to the time the magnetic tape travels from the position of the full-width erasing head to the recording/reproducing start end of the rotary head from when the capacitor 35 is fully charged. The voltage is set to be the voltage observed between the terminals of the capacitor 35 after discharge.

Therefore, the shot trigger circuit 48 generates an output (FIG. 5(e)) when the time for the magnetic tape T1 to travel from the full-width erasing head position to the recording/reproducing start end of the rotary head at the end of editing has been exceeded. Trigger the sixth monostable multivibrator 46. The output (FIG. 5) is applied to the first and second gate circuits 51 and 52 via the edit changeover switch ED1 in the OFF position, opening these circuits.
A fourth circuit whose trigger inputs are the output of the first monostable multivibrator 41 (FIG. 5 C) and the output of the third monostable multivibrator 43 (FIG. 5 N), respectively.
The output of the monostable multivibrator 44 (FIG. 5 L) is passed through (FIG. 5 T, W), and the subsequent second and fifth monostable multivibrators 42 and 4, respectively.
5, and the corresponding switching transistors Tr1 and Tr3 are made non-conductive via the editing changeover switches ED2 and ED3, which are switched to the OFF position (each output is shown in FIGS. 4 and 7). De-energize relays L1 and L2 and switch switches S8 and S9 from the recording position to the playback position (Fig. 5 A and R) At the same time, switch S10 and S11
is turned off, cutting off the supply of erase current to the rotating erase heads H3 and H4.

At this time, the switch S12 that controls the power supply to the erase oscillator circuit 39 is also turned off at the same time, but if the supply of erase current to the full-width erase head is not cut off before then, the magnetic There are blank spaces or areas where new and old video information intersect on the tape. Therefore, the switch S13 is activated when the edit changeover switch ED5 is switched to the off position.
It is configured to be switched to the OFF side to temporarily cut off the supply of erase current to the full width erase head 4. That is, when the edit changeover switch ED5 is switched to the OFF side, the Schmitt circuit 56 is reversed to turn off the switching transistor Tr5, deenergize the relay L3, and temporarily turn off the switch S13.

The Schmitt circuit 56 is set at a low operating level. Therefore, by the time the terminal voltage of the capacitor 54 discharged through the resistor 55 drops and the Schmitt circuit 56 is reversed, the editing/recording operation has been completely completed, the switch S12 has also been turned off, and the operation is started again. Even if the switch S12 is turned on, no trouble will occur.

In place of the pulse generator PG3 in the above embodiment,
By providing a detection coil at a specific position in the tape non-contact section of the magnetic head and using its shaping output, the monostable multivibrator 41 and the like can be omitted.

In addition, the pulse generator PG for the above switching
1, PG2 or a combination of the output of the rotational phase detection means used for rotational phase control of the rotary head and a monostable multivibrator for delay.

Since the present invention has the above-described configuration, the switching of the magnetic head to the recording system and the reproducing system at the start and end of editing recording is all performed at the time when the magnetic head is not in contact with the magnetic tape, so that there is no switching noise. This solves problems such as the synchronization of edited and reproduced images being disrupted.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the magnetic tape around the guide cylinder, each rotary head, and the full-width erasing head, Figure 2 is an explanatory diagram of the optimal timing for switching the rotary head to the recording and reproducing system, and Figure 3 is of the present invention
A circuit block diagram showing an example of an implementation circuit of the VTR editing device, and FIGS. 4 and 5 each show an explanatory diagram of operating waveforms. H1, H2... Rotating head, H3, H4... Rotating erase head, 30 ... Edit switching circuit, 33 ...
Edit end signal generation circuit, 34 ...Erasure control circuit.

Claims (1)

[Claims] 1. In a two-head helical scan VTR equipped with a capstan servo device, when insert editing recording starts, a pulse is generated at an arbitrary time during the half-rotation period when the rotating heads H1 and H2 are in a non-contact state with the magnetic tape. The outputs of the pulse generators PG3, 20, and 41 are taken out through gate circuits 51 and 52 that operate in conjunction with the operation of the means for commanding the start of recording in the editing standby mode, and the VTR is switched from the playback mode to the record mode. ,
At the end of editing recording, delay means 48 and 46 which operate in conjunction with the operation of the means for instructing the end of editing recording cause the output of the editing recording terminating means to be delayed so that at least the magnetic tape is at the position of the full-width erasing head. The rotation head is delayed by a time sufficient for the rotary head to travel to the recording start position, and the gate circuits 51 and 52 are controlled by the delayed output, and the output of the pulse generator passing through the gate circuit causes the rotary head to rotate. A VTR editing device configured to end editing recording in the tape non-contact section of the head.