JPS6117391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scan type magnetic recording and reproducing apparatus (VTR), which is configured to reproduce still images in good quality with a simple configuration.

As is well known, in a helical scan VTR, if the magnetic tape is played back while stopped, a still image can be played back.

However, since the scanning locus of the rotating head on the magnetic tape when the tape is stopped is different from the recording locus, it is not possible to accurately scan one recording locus, resulting in a period in which no reproduction signal is obtained.

By locating this period in which no reproduced signal is obtained in the vicinity of the vertical synchronizing signal, substantially less damage can be displayed on the television receiver.

The position on the playback screen during this period when no playback signal is obtained varies depending on the positional relationship between the rotation trajectory of the rotary head and the recording trajectory, that is, the stop position of the magnetic tape.
I looked at the playback screen and moved the magnetic tape slightly to get the best image.

The present invention is configured to automatically obtain an optimal image, and will be described below by giving examples thereof with reference to the drawings.

Figure 1 shows a two-head helical scan type
The recording trajectory of the VTR and the trajectory of the video head during still image playback are shown. The head gap angles of the two video heads are slightly different, resulting in azimuth recording. Therefore, tracks a ₁ , a ₂ , a ₃ . . . recorded on the A head side are reproduced only on the A head, and tracks b ₁ , b ₂ , b _{3 .} . . recorded on the B head side are reproduced only on the B head. It is not possible. FIG. 2 shows the envelope of the head output during still image playback, and lines A and B in FIG. 2 correspond to playback trajectories 1 and 2 in FIG. 1, respectively. In the case of trajectory 1, the section where the envelope disappears becomes the head switching point, and just enters the vertical blanking section. Trajectory 2
In this case, it will be located within the screen. The envelope output becomes small and the area around O becomes a noise band in the reproduced image. Figure 2C shows the waveform when the head output is passed through a limiter. That waveform
The waveform when AM is detected is 2. In the present invention, the waveform D is detected to determine which track the head is currently playing. That is, the tape is run until the detected output pulse 2 comes near the head switching position.

FIG. 3 shows a basic configuration diagram of the present invention, and FIG. 4 shows waveforms of each part thereof.

When the VTR is in the normal playback mode, a motor control signal is passed from the input terminal 3 through the gate 4 to the motor drive circuit 5 to control and drive the capstan motor 6. When the switching signal (PLAY/STILL) a between normal playback and still image playback is switched to the STILL mode, the gate 4 is cut off and the gate 7 is turned on. The output signal d of the gate 7 controls and drives the capstan motor 6 via the motor drive circuit 5. However, at the moment when the switching signal a switches to the STILL side, the differentiating circuit 8 operates, and its output signal C momentarily shuts off the gate 7, and also activates the motor brake circuit 9 to stop the capstan motor. Apply the electromagnetic brake to 6 to stop the tape from running. After that, the output control signal d of gate 7
The capstan 6 is controlled and driven. The head switching pulse (30Hz) g corresponding to the rotational phase of the rotating head is Δt at MM (mono multi) 10.
After the phase is shifted by 1, the MM11 generates a thin pulse h. The pulse h is used as a set signal for the FF (flip-flop) 12, and also as a set signal for the gate 13.
used as a gate signal. Head output RF
The signal k becomes a pulse j that is used by the detection circuit 14 to detect a section in which the envelope output falls below a predetermined level. Pulse j is used to determine what kind of track the head is currently playing. That is, pulse j is gated at gate 13 by gate pulse h. The signal i is output from the gate 13 only when the pulse j matches the phase of the gate pulse h. Signal i is FF1
In the FF 12 which operates as a reset signal of 2, when there is a set signal h and there is no reset signal i, a high level signal f appears at the Q terminal.
On the other hand, when there is a reset signal i, the Q terminal becomes Low level and the terminal becomes High level. The high level is supplied to the motor brake circuit 9 via the gate 15. The gate 15 is ON-OFF controlled by the switching signal a, and is in a conductive state only in the STILL mode. In other words, switching signal a is STILL
When switching to the side, an electromagnetic brake is momentarily applied to the capstan motor 6, and the motor stops. Thereafter, it is controlled by the output signal f of the FF12. The level of the signal f is set so as to rotate the motor slowly. When the tape travels slowly and the noise band detection signal j approaches the switching point of the head switching pulse and matches the phase of the pulse h, the FF12 enters the reset state, the signal f becomes 0, and the signal to the motor is At the same time as the control signal is stopped, a motor brake signal is generated from the terminal to instantly stop tape running. Therefore, the position of the noise band is maintained in the vertical blanking interval. In this manner, in the present invention, when switching from PLAY mode to STILL mode, the tape always stops at a position where the noise band becomes a vertical blanking section, so a still image without a noise band is seen. Here, electromagnetic braking of the motor may be applied to stop the tape from running.
At this time, the brake solenoid can be controlled in the same way.

In fact, in order to make the noise band width as narrow as possible, the track width of the head should be made slightly wider than the pitch of the recording pattern.

In this example, the noise band gate signal h is 30
Every Hz, that is, every frame, but 60Hz
It may be for every field, that is, for every field.

According to the above configuration, the magnetic tape is automatically stopped at a position where a good still image can be obtained, but due to fluctuations in the reproduction output level of the magnetic head, the tape stopping position may be at the optimum position. Sometimes it doesn't.

That is, when a still image is reproduced, the envelope of the RF signal becomes close to a triangular wave, as shown in k in FIG. AM this envelope
When detecting a level at a predetermined arbitrary constant level and generating signal j, if the peak level of the envelope is not kept within a certain range, the pulse width of signal j will change. do.
If this pulse width becomes too wide, the phase relationship with the gate signal h will become poor, making it impossible to accurately hide the noise band in the blanking section. This situation is shown in FIG. Figure 5 A shows the RF signal k
This shows that the level of is changing from a to b to c. B indicates that the pulse width of signal j changes when the RH signal level changes.

As the level of the RF signal k decreases and the pulse width of the signal increases, the stop of the tape is determined by the position of the signal h within this pulse width.
The tape stop position is not the lowest position of the envelope of the reproduction signal k, and a noise band appears on the reproduction screen.

On the other hand, if the level of the reproduced signal k becomes too high, the pulse width of the signal j becomes too narrow, which may make the device inoperable.

Level fluctuations in the reproduction signal k occur due to temperature changes, tape compatibility, reproduction demagnetization, and the like.

The present invention aims to solve this problem as well, and an embodiment thereof is shown in FIG.

The reproduced RF signal k is amplified by the amplifier 20 and
The detector 21 performs envelope detection. The level discriminator 22 uses this envelope to generate a signal j having a pulse width corresponding to a period below a predetermined level.

The above operation is the same as 14 in FIG. 3. This signal j is amplified by an amplifier 23 and converted to a DC level according to the pulse width by an integrating circuit 24 to generate a signal l. This signal l is fed back to the level discriminator 22 and its detection level is controlled so that the pulse width of the signal j is always a certain constant width.

FIG. 7 shows the waveforms of each part. In FIG. 7, A shows the reproduced signal k, B shows the output signal j of the level discriminator 22, and C shows the output signal l of the integrating circuit 24.

In addition, in Figure 7 A and B, the solid line indicates the discriminator 2.
If there is no feedback in 2, the dotted line indicates the presence of a feedback loop. In this way, by providing the level discrimination circuit 22 with a feedback loop, stable noise band detection can be performed with respect to fluctuations in the reproduced signal level.

FIG. 8 shows a configuration diagram when a dropout detection mechanism, which is a function within the VTR body, is used for noise band detection operation. In Figure 8,
A and B are video heads, and the reproduced outputs are led to a head switching circuit 28 via amplifiers 26 and 27, respectively, and converted into a series of signals by head switching pulses.
The signal is led to a switching circuit 30 and a dropout detection circuit 31 via an amplifier 29.

This dropout detection circuit 31 has a configuration shown in the dotted line frame 14 in FIG.
It generates a predetermined output.

The switching circuit 30 is driven by the output of the detection circuit 31, and the movable contact of the switching circuit 30 is switched to the terminal b only when the envelope becomes below a predetermined level, that is, only during the dropout period.
This is to switch to . Reference numeral 31 is a delay circuit for one horizontal scanning period, 32 is a limiter circuit, and 33 is an FM detection circuit.The above configuration is a dropout compensation mechanism that is generally built in a VTR.

A part of the output of the dropout detection circuit 31 is sent to an amplifier 23, an integrating circuit 24, and a changeover switch 34.
The dropout detection circuit 31 is configured to provide feedback to the dropout detection circuit 31 via the still image reproducing operation, and is configured to drive the changeover switch 34 in conjunction with the still image reproducing operation to apply the feedback. The noise band detection signal j is obtained as the output of the dropout detection circuit 31 by performing the same operation as shown in FIG.

FIG. 9 shows another embodiment of the present invention,
The difference from FIG. 6 is that after the RF signal k is passed through an amplifier 35, it is passed through a detection/integration circuit 36 to a DC signal (7th
The configuration shown in FIG. d) is fed back to the level discrimination circuit 22.

As described above, according to the present invention, the magnetic tape is automatically stopped at a position where an optimal still image can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the tape pattern and still image playback trajectory in the azimuth recording method, Fig. 2 is a diagram showing the envelope waveform and noise band waveform in each playback trajectory in Fig. 1, and Fig. 3 is the basics of the present invention. 4 is a waveform diagram showing the operation of each part of FIG. 3, FIG. 5 is a waveform diagram for explaining the operating principle of the present invention, and FIG. 6 is a block diagram showing one embodiment of the present invention. , FIG. 7 is a waveform diagram of the same operation, and FIGS. 8 and 9 are block diagrams showing an embodiment of the present invention. 4, 7, 13, 15...gate circuit, 5...motor drive circuit, 6...capstan motor,
8...Differential circuit, 9...Motor brake circuit, 1
2...Flip-flop circuit, 14...Detection circuit, 20, 23...Amplifier, 21...AM detection circuit, 22...Level discrimination circuit, 24...Integrator circuit.

Claims (1)

[Claims] 1. Means for switching the capstan to low-speed drive when switching from the normal reproduction state to still image reproduction, and a pulse corresponding to the period during which the level of the envelope of the reproduction output of the rotary head falls below a predetermined detection level. means for obtaining an AND output between the pulse and a head switching pulse of the rotary head; and means for stopping the capstan being driven at low speed by the AND output;
A rotating head type magnetic recording and reproducing apparatus comprising detection level control means for controlling the detection level so that the width of the output pulse of the level discrimination means is constant. 2. The rotary head type magnetic recording and reproducing apparatus according to claim 1, wherein the detection level control means is configured to control the detection level according to the output pulse width of the level discrimination means. 3. The rotary head type magnetic recording and reproducing apparatus according to claim 1, wherein the detection level control means controls the detection level according to the average value of the envelope level of the reproduction output. 4. The output pulse of the level discrimination means is also used as a drive pulse for the dropout compensation means, and the detection level control means is operated only when reproducing a still image.
The rotary head type magnetic recording and reproducing device described in 2.