JPS624035B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing apparatus that allows still images to be reproduced satisfactorily.

Rotating head type magnetic recording and reproducing devices, e.g.
In VTRs, etc., it is possible to perform high-speed operation or slow-motion image playback by changing the running speed of the magnetic tape while the rotary head drum is rotating, and it is also possible to perform playback by stopping the running of the magnetic tape. If this is done, it will also be possible to reproduce still images, which will expand the uses of the magnetic recording and reproducing apparatus and make it more versatile.

On the other hand, in order to meet the demand for increased recording times, the azimuth method, which enables high-density recording, was adopted as a recording method for magnetic tape, and as this method has ceased to be the mainstream in VTRs, new problems have arisen when playing back stills. has occurred.

Generally speaking, to perform still playback (still image playback) from a magnetic tape recorded at a standard tape speed (1x), it is sufficient to simply stop the running of the tape.

However, if the running of the tape is stopped randomly, the trajectory of the rotating magnetic head relative to the recording track during playback may not always be in an optimal state.
Noise bands often appear on the reproduced image plane, making it impossible to obtain a satisfactory still image.

This state is particularly noticeable in the case of the azimuth recording method, and poses a major practical obstacle. To explain this situation with a drawing, in Fig. 1, A ₁ and A ₂ are tracks by one of the two heads, for example, the A head, and B ₁ and B ₂ are tracks by the other head, for example, the B head. A ₁ and A ₂ are A azimuth tracks, and B ₁ and B ₂ are B azimuth tracks. As is well known, the azimuth recording method consists of two
By setting the gap angles of the heads to be different, a track recorded by one head will produce a signal with the maximum amplitude when played back by that head, but if this is traced by the other head, the signal will have the maximum amplitude. This method enables high-density recording by ensuring that almost no reproduction signal is obtained, thereby preventing crosstalk between adjacent tracks even if mistracking occurs.

Therefore, tracks A ₁ , A 2 , A ₂ on the magnetic tape (stopped) when in still playback mode.
When B ₁ , B ₂ and the trajectory 1 formed by the rotating head are in the relative positions shown in Figure 1, the trajectory 1 is almost on the B ₁ track, so when the B head traces it, an almost complete image is created. A signal is obtained for one field, but when traced with the A head, a dropout occurs in the center of one field and the signal is missing, and as a result, noise appears in the center of the reproduced still image plane 2 as shown in Figure 2. Band 3 appears.

Moreover, the signal obtained when being traced by the A head is that the first half of one field is
The second half is played from the A ₁ track, and the latter half is played from the A ₂ track, and since these originally form different fields, there is naturally a line skip between them, and in the end, in the field played by the A head, The upper and lower parts of the screen 2 will shake differently up and down, making the image even more difficult to view.

On the other hand, when the tape stops at the relative position shown in Figure 3, almost one complete field is traced from the _A2 track when tracing with the A head, and from the _B1 track when tracing with the B head. You will get a video signal of
An easy-to-see still image without noise bands, such as image 2 in FIG. 4, can be obtained.

Therefore, when switching to still playback operation,
The magnetic tape must always be stopped at the relative position shown in FIG.

Therefore, in the past, each time you switched to still playback, you manually moved the magnetic tape and made adjustments while looking at the image plane so that the trajectory of the recording track and rotating head was as shown in Figure 3. .

In addition, in order to do this automatically, the FM envelope of the reproduced video signal is at its maximum (corresponding to the center of the screen), or the FM envelope is at its minimum (at the vertical retrace period outside the screen). A method has also been devised in which the tape is detected (when a dropout occurs) and the running of the tape is stopped.

However, in reality, capstan motors have large inertia, and simply disconnecting the motor drive power will cause the tape to move several to tens of fields, making it impossible to stop it at the correct position. It is almost impossible, and even if you try to control the amount of movement by anticipating the amount of movement in advance, there will be a lot of variation in the amount of movement, so it is necessary to automatically stop the tape at a position that will drive the noise band off the screen. It was extremely difficult to put the device into practical use.

Of course, it is possible to mechanically stop the capstan motor suddenly, but it is difficult to maintain a constant movement amount all the time. has a fairly sophisticated control mechanism, making it nearly impossible to realize from a cost standpoint.

An object of the present invention is to provide a magnetic recording and playback system that eliminates the drawbacks of the prior art described above, and that automatically stops the tape at a position where no noise band occurs on the screen during still playback, so that a still image that is easy to see is always obtained. We are in the process of providing equipment.

In order to achieve this object, the present invention sufficiently reduces the running speed of the magnetic tape using a still playback operation switching signal before stopping the magnetic tape, detects dropout of the video signal due to mistracking, and detects the dropout of the video signal due to mistracking. The present invention is characterized in that it is possible to obtain the amount of movement of the tape after stop control and to keep the amount of movement of the tape within a predetermined amount.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 5, 5 is a magnetic tape, 6 is a rotating head, 7 is a tack head for detecting the rotational phase of the rotating head 6, 8 is a head motor, 9 is a capstan, 10 is a capstan motor, and 11 is the rotating head 6. 12 is a dropout detection circuit that detects the dropout of the video signal and generates a signal; 13 is a delay circuit that delays the signal from the task head 7; 14 is a comparator, 15 is a delay circuit, 16 is a differentiation circuit, 17 is an AND gate, 18 is a delay circuit, 19 is an OR gate, 20 is an RS flip-flop with set priority, 21 is a delay circuit, 22 is a differentiation circuit, 23 is a switch element,
24 is a capstan control circuit.

The magnetic tape 5 is run in the direction of the arrow by a capstan 9 driven by a capstan motor 10, and a recording pattern is traced by a rotary head 6 rotated by a head motor 8 to reproduce a video signal N. supplied to

The tack head 7 detects the rotational phase of the rotary head 6 to generate a rotary head tack signal P, and a delay circuit 13 applies a predetermined delay to generate a head switching signal C.

A frequency modulated reproduction signal Q is taken out from a signal system 11, and a dropout of its envelope is detected by a dropout detection circuit 12 to obtain a dropout signal R.

This dropout signal R is supplied to a comparator 14, and only the dropout signal above a predetermined level is shaped into a dropout output F. At this time, if an integrating circuit is provided at the input of the comparator 14, malfunctions due to noise can be eliminated.

Further, a signal D obtained by delaying the head switching signal C by a delay circuit 15 is applied to a differentiating circuit 16 to obtain a sampling pulse E.

Then, these dropout output F and sampling pulse E are applied to the AND gate 17, and when they match, an output G is generated and is used as a reset input of the flip-flop 20.

On the other hand, when a still playback operation is performed, a still playback operation switching signal A is generated, and this signal A is delayed by the delay circuit 18 to create a signal B, which is supplied to the OR gate 19 together with the original signal A. The output is applied as an inhibit signal H to the set input S of flip-flop 20.

The Q output of flip-flop 20 is supplied to capstan control circuit 24 as motor stop output I.

Next, the operation of this embodiment will be explained with reference to FIG.

In FIG. 6, the upper curve shows the moving distance d of the magnetic tape 5 with respect to the elapsed time T, and the time
At _T1 , a switching operation to still playback is performed and signal A is generated. Note that before time _T1 , the tape is running at a standard speed or an arbitrary speed, indicating that playback is being performed.

When a switching operation is performed at time _T1 and signal A is applied, capstan control circuit 24 reduces supply voltage J to capstan motor 10 to a predetermined value. The magnitude of this reduced voltage J is such that the rotation of the motor 10 thereby causes the tape 5
The traveling speed of the tape 5 is not in an integer ratio with the standard playback speed, but is low enough so that when the voltage J is set to 0, the moving distance of the tape 5 is within the distance equivalent to one field. put.

As a result, the running speed of the magnetic tape 5 decreases,
A deviation occurs in tracking and causes a dropout in the video signal being reproduced from the head 6, which is generated as a dropout signal R from the detection circuit 12, and a dropout output F begins to be applied to one input of the AND gate 17.

This dropout output F is matched by the sampling pulse E, and when the dropout output F matches, the output G
An attempt is made to reset flip-flop 20 as follows.

However, the signal B delayed from the signal A by the delay circuit 18 is sent from the output of the OR gate 19 as the inhibition signal H to the set input S of the flip-flop 20.
This flip-flop 2
0 has not yet been reset.

Therefore, even if the coincidence output G is generated between time _T1 and _T2 determined by the time constant of the delay circuit 18, the flip-flop 20 is not reset.

At time _T2 , signal B disappears and prohibition signal H
becomes 0, during which time the capstan motor 10 overcomes its inertia and settles to the reduced speed.

Then, after time _T2 , the time when the dropout output and the sampling pulse E first coincide.
Since the flip-flop 20 is reset by the coincidence output G generated at _T3 , the motor stop output I is applied to the capstan control circuit 24 from the output Q, and the voltage J supplied to the motor 10 becomes 0. The motor 10 stops at time _T4 after the tape 5 has moved a distance equivalent to one field (actually, it can be set to about 10% of one field).

Now, if we pay attention to the phase of the sampling pulse E in FIG. Therefore, the phase of pulse E is a predetermined lead phase with respect to the vertical retrace period of one field. Moreover, the amount of the advanced phase can be arbitrarily determined by the time constant of the delay circuit 15.

Therefore, if the time constant of the delay circuit 15 is set to an appropriate value and the lead phase amount of the sampling pulse E relative to the signal C is set to be approximately 10% of one field, the motor stop output I will be as shown in Fig. 3. This occurs when the magnetic tape 5 reaches a position within 10% of one field, and the voltage J of the motor 10 is set to 0, before the magnetic tape 5 reaches the optimum position shown in .

Therefore, the motor 10 stops at time _T4 when the tape 5 reaches the optimum position, and still images are produced in the best condition.

Here, even if the motor voltage J is reduced at time _T1 , it does not immediately reduce to the predetermined speed due to the inertia of the motor 10, so the time required for the speed of the motor 10 to reach the reduced speed and stabilize ( Approximately 0.5
seconds), that is, from T ₁ to T ₂ (T ₂ - _{T 1} =
0.5 seconds), the signal H prohibits the flip-flop 20 from being reset by the coincidence output G.

Therefore, the speed of the motor 10 can be set to a sufficiently low speed that the moving distance of the tape 5 after the voltage J is set to 0 can be reliably kept within about 10% of one field.

In addition, since the running speed of the magnetic tape 5 is sufficiently low after switching to still playback, that is, after time _T1 , the amount of movement of the tape 5 until starting still playback at time _T4 is calculated. Since the screen can be suppressed to about a field, the screen can be stopped almost at the desired location, and the necessary still image can be obtained in good condition.

As already explained, the tape running speed reduced at time _T2 must be sufficiently low and must not have an integer ratio with the speed during standard playback. If it is a fraction of an integer, the phase of the dropout output F will be the switching signal C.
and the sampling pulse E becomes constant, and the relationship between the head 6 and the recording track of the tape 5 remains constant, and the dropout output F does not occur before the optimum position. This is because you get used to it. In FIG. 6, the speed must be such that the phase of the output F is constantly changing with respect to the pulse E.

A specific example of the capstan control circuit 24 is shown in FIG.

31 is a control circuit provided as an original part of the magnetic recording device; 32 is a switch element which is switched by a signal A as a power source 34 for supplying a low voltage to the motor 10 from time T ₁ to T ₃ ;
35 is a switch element that is opened by the motor stop output I.

Until the operation to switch to still playback is performed at time _T1 , the voltage for standard playback or playback at an arbitrary speed is applied from the control circuit 31 to the capstan motor 10 through switch elements 34 and 35.
However, when signal A is applied at time _T1 , switch element 34 is switched, and power supply 3
2 is supplied to the motor 10 and the tape 5
The traveling speed of is changed to a predetermined lower speed.

Then, at time _T3 , motor stop output I is applied, switch element 35 opens, and voltage J becomes zero. Note that, if necessary, the motor 10 may be electrically braked.

By the way, another problem during still playback is the deterioration of the vertical synchronization signal.

That is, during still playback, the noise band is pushed within the vertical synchronization period in order to obtain the best still image. In other words, a dropout occurs within the vertical synchronization period, and the level of the vertical synchronization signal decreases or even disappears in some cases.

As a result, vertical synchronization becomes unstable or synchronization is lost.

Therefore, in the embodiment shown in FIG.
An additional vertical synchronization signal is added to the vertical synchronization signal reproduced in the above, thereby perfecting the vertical synchronization during still playback to obtain a stable still image.

This will be explained below as shown in Figures 3 and 5.
In Fig. 8, during still playback, the trace state is as shown in Fig. 3, so that the degraded vertical synchronizing signal T is obtained from the A head after a delay of _t1 from the head switching signal C and from below the dropout output. Then, it can only be obtained from the B head in the next field after _t2 .

This is because the tape 5 has stopped and tracing is not started from the recording track by the regular B head.

Therefore, the head switching signal C is delayed by the time (t ₂ - t ₁ ) in the delay circuit 21 to obtain the signal K, and either the rising portion or the falling portion thereof is differentiated in the differentiating circuit 22 to obtain the pulse L. A switch element 2 whose pulse L is closed by a signal A
3, it is added as a vertical synchronization signal M only during playback.

As a result, the correct vertical synchronization signal M is supplied even during still reproduction, so there is no fear that the reproduced still image will become unstable, and a stable and easy-to-see still image can be obtained.

At this time, when differentiating the signal K in the differentiating circuit 22, whether to differentiate the rising part of the signal K or the falling part to obtain the vertical synchronization signal L depends on the vertical retrace period of which frame. It is desirable to select and determine the one that will result in better still playback operation.

As described above, according to the present invention, noise bands that appear on the screen during still playback can be automatically removed from the screen to obtain a stable, easy-to-see still image. Therefore, there is no need for manual adjustment as in the prior art, and a stable still image can always be obtained. In addition, since everything is configured using electrical control, there is no need to make any changes to the mechanical parts, and the factors that increase costs can be reduced.

Furthermore, in the configuration of the present invention, delay circuits, logic circuits, etc. used in each part are integrated into a single chip.
It is also possible to use an IC or a microcomputer, which reduces the number of parts, provides reliable operation, and prevents increases in costs.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the recording track on the magnetic tape and the locus of the rotating head during still playback;
Figure 2 is a schematic diagram showing the noise bands that occur on the still image playback surface, and Figure 3 is a plan view showing the recording track and the locus of the rotating head when the magnetic tape is stopped at a position where no noise bands occur. , FIG. 4 is a schematic diagram showing a reproduced image thereby, FIG. 5 is a block diagram of a magnetic recording and reproducing apparatus according to an embodiment of the present invention, FIG. 6 is a characteristic diagram and waveform diagram for explaining its operation, and FIG. FIG. 7 is a block diagram showing a specific example of the capstan control circuit, and FIG. 8 is a waveform diagram for explaining the operation of adding a vertical synchronizing signal. 5... Magnetic tape, 6... Rotating head, 7...
Tack head, 11...Video signal system, 12...Dropout detection circuit, 13, 15, 18, 21
...Delay circuit, 14...Comparator, 16, 22...
Differential circuit, 17...AND gate, 19...OR gate, 20...Set priority RS flip-flop, 23...Switch element, 24...Capstan control circuit.

Claims (1)

[Claims] 1. In an azimuth recording type magnetic recording/playback device having a still playback mechanism, when a switching signal is applied from a playback operation other than a still playback operation to a still playback operation, the traveling speed of the magnetic tape is changed to Means for reducing the standard playback speed to a preset low speed when the phase of dropout occurrence in the playback signal is not in a predetermined integer relationship that is a constant relationship with the video signal, and a magnetic tape after the running speed has been reduced. detecting means for detecting the presence or absence of dropout in the video signal reproduced from the vertical flyback period at each point in time preceded by a predetermined phase relative to the vertical retrace period; and a detection signal from the detecting means to apply reverse braking to the capstan motor. What is claimed is: 1. A magnetic recording and reproducing device characterized by comprising means for applying and stopping the magnetic recording and reproducing device. 2. In the magnetic recording/playback device according to claim 1, during still playback operation, a vertical synchronization signal is created from a signal corresponding to the rotation of the rotating magnetic head drum, and the azimuth of the recording track to be traced on the stopped tape is adjusted. 1. A magnetic recording and reproducing device characterized by comprising means for changing the phase of the created vertical synchronizing signal according to the difference and adding it to a reproduced video signal.