JPH0118632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating head type video tape recorder (hereinafter referred to as VTR), and particularly relates to a rotating head type video tape recorder (hereinafter referred to as VTR), and in particular, a magnetic tape is run intermittently so that no noise bars appear on the playback screen and the magnetic tape is continuously played. The purpose of this is to realize slow playback and still playback that correspond to slow speed changes.

Conventionally, there are two methods of slow and still playback in VTRs that do not cause noise bars to appear:

The first method is to attach a rotary head to a drive element such as a piezoelectric element, so that it can be displaced in the axial direction of the cylinder, and to scan a desired recorded track even if the tape speed during playback changes. This is to move the head. In this method, the tape is running continuously, and in order to move the head accordingly, complex waveforms related to tape speed information during playback, playback control signals, head switch signals, etc. must be created as signals to the piezoelectric element. It won't happen. That is, different drive waveforms must be prepared for every tape speed. In particular, in order to continuously change the throw ratio, it is necessary to continuously detect the playback tape speed, and when the throw is very slow, the control signal cannot be detected with a normal head. Therefore, the system becomes extremely complex. Furthermore, an auto-tracking servo for automatically correcting track deviations during playback is required in addition to the servo of the conventional tape drive system, and the circuit size becomes considerably large. In this way, the first method can realize slow and still playback without noise bars, but it has the disadvantage that it requires an extremely expensive VTR to achieve this.

The second method is to drive the tape in two modes, a running state and a stopped state, during playback, drive the tape intermittently, and obtain a playback signal with a playback head having a track width wider than the recording track width. This achieves a slow ratio of . This method allows arbitrary slow playback simply by controlling the drive of the tape, and can be said to be relatively easy to configure. However, there are the following problems. The point is that it is necessary to use a reproducing head whose track width is wider than the recording track width. The reason for this is that, as is well known, the scanning locus of the rotary head when the tape is stopped is different from the recording track, so the width of the playback head must be widened so that it can pick up signals from the same track even in that state. be. This may not be a major problem for a single-time mode VTR, but for a multi-time mode VTR, it is necessary to prepare a head with a track width corresponding to the number of time modes, which increases the complexity of the device. Become. for example,
VCRs that can record and play back 2, 4, and 6 hours on the same tape cannot achieve slow playback without noise bars in all time modes unless they have three sets (six) of rotating heads. Can not.

The present invention aims to eliminate the shortcomings seen in the conventional slow motion playback methods as described above, and is compatible with multi-time mode VCRs and capable of continuous speed changes by relatively simple means. The present invention provides a slow motion playback method that enables beautiful slow playback without noise bars.

Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 is a model diagram of a group of rotating heads used in the present invention, in which four rotating magnetic heads (hereinafter referred to as
(referred to as heads) 3, 4, 5, and 6 are attached. Here, 3 and 4 are recording/playback heads having different azimuth angles, similar to a conventional VTR, and these are fixedly mounted on the cylinder 2 at a position of 180 degrees.

On the other hand, numerals 5 and 6 are rotary heads dedicated to reproduction having the same azimuth angle, and the azimuth angle matches the azimuth angle of either of the rotary heads 3 or 4. The rotating heads 5 and 6 are attached to the free ends or tips of drive elements 7 and 8, such as bimorph piezoelectric elements, which are electro-mechanical conversion elements, and are driven by the drive elements 7 and 8 to drive the cylinder. It has a structure that allows it to move up and down in the length direction of the shaft. Note that the other ends of the drive elements 7 and 8 are attached to the rotating drum 2. During recording, the rotating heads 3 and 4 convert the video signal into 1 field per field.
The diagonal tracks of the book are recorded on the magnetic tape, with azimuth angles alternating from field to field.

FIG. 2 is a diagram showing a track pattern on a recorded magnetic tape. The magnetic tape 11 runs in the direction of arrow F during recording, and the tracks recorded sequentially are A ₁ , B ₁ , A ₂ , B ₂ . , A ₃ , B ₃ , A ₄ , B ₄ ......
is shown. Here, A ₁ , A ₂ , A ₃ , . . . are tracks recorded by the same recording head, for example 3 in FIG. 1, and B ₁ , B ₂ , B ₃ , . This is the track recorded at (4 in Figure 1). If the magnetic tape 11 recorded in this way is run at the same speed during playback and is played back alternately by the rotary heads 3 and 4, the signals A ₁ ,
It is well known that the moving images are obtained in the order of B ₁ , A ₂ , B ₂ , . . . and the same moving image as that during recording is obtained.

In the still mode in which the magnetic tape 11 is stopped during reproduction, for example, if the track width of the reproducing rotary head is the same as the recording track width, the scanning locus of the reproducing rotary head will be 1 as shown by the broken line 12 in FIG. It will recline by an angle equal to the track pitch. If the azimuth angles of rotary heads 5 and 6 are, for example, the same as the azimuth angle of rotary head 3 and are A azimuth shown on the tape pattern in _FIG . In the upper part of the figure, the signal is missing, resulting in noise bars on the playback screen. Here, in order to play all of track A ₂ even if the magnetic tape is stopped during playback,
It is sufficient to move the rotary head by one track pitch in the track width direction (to the right in the figure) during the first field period (1/60 second) during which the rotary head 5 contacts the magnetic tape. In the second field, the rotating head 6
comes into contact with the magnetic tape and attempts to scan the track locus 12, so it is only necessary to similarly move it one track pitch in the width direction. By doing so, the second field also has the rotating head 6 track A ₂
Thereafter, the rotary heads 5 and 6 will alternately reproduce the same track _A2 , realizing field still reproduction. The rotational heads 5 and 6 can be moved by applying appropriate voltage waveforms to the head drive elements 7 and 8.
FIG. 3 shows the amount of deviation (or the voltage applied to the head drive elements 7 and 8) on the vertical axis and the time on the horizontal axis. The period indicated by the broken line in FIGS. 3a and 3b is a period in which the rotating head is not in contact with the magnetic tape, and the waveform may not be the one shown.

As is clear from FIG. 3, the voltage waveform applied to the drive element in the still mode can be an extremely simple triangular wave with one cycle of two fields.

Next, slow motion playback will be explained.
In this case, since there is a state in which the magnetic tape moves, an explanation using the tape pattern diagram of FIG. 2 would be complicated, so the description will be made using the tracking state description method shown in FIG. 4a. The horizontal axis of FIG. 4a indicates time, and the head switch signal of FIG. 4b, which is a 30 Hz rectangular wave, is considered as a reference. The vertical axis indicates the amount of tape movement and also indicates the track width and head thickness. Therefore, A ₁ is the recording track A ₁ in FIG.
are repeatedly described, and B ₁ is a track B ₁ with a different azimuth. When the magnetic tape is played back at standard speed (same speed as when recording), the magnetic tape is fed one field pitch during one field period of the head switch, so the trajectory of the rotating playback head at that time is shown in the figure. The angle is 45 degrees, and the tracks to be played are A ₁ , B ₁ , A ₂ ,
The order is B ₂ , A ₃ ..., and normal playback occurs.
Also, when the tape is stopped, the
Since the magnetic tape does not move, it follows a horizontal trajectory on the horizontal axis, and if the track width and head width are the same, only half of the signal on each track will be reproduced and a noise bar will appear. As already mentioned, there is a method that achieves noise-free still images by reproducing this with a wide rotating head. In a structure in which the rotary head is attached to a movable part of a head drive element such as a piezoelectric element and can be moved in the vertical direction, as in the present invention, a triangular waveform deflection as shown in Fig. 3 can be applied completely. Figure 4a shows that it is possible to match the same track and achieve noise-free still playback.
This can be easily understood from.

In slow motion playback, the magnetic tape is intermittently fed in synchronization with the rotation of a rotary drum to which a rotary head is attached, ie, with the head switch signal shown in FIG. 4b. The speed at which the tape moves should preferably be at standard playback speed.
Generally, tape drive motors have inertia, so it is difficult to reach standard speed in a short period of time. Therefore, the tape moving speed must be selected to be 1/2 to 1/4 of the standard speed. In the example of FIG. 4, as shown in c, the tape movement speed is set to 1/2 of the standard speed. At standard speed,
2 to move from _A1 track to _A2 track
Since a field period is required, in this case, the feed rate is 1/2 and four field periods are required. It goes without saying that the tape speed O in FIG. 4c indicates a still state. The head trajectory when the tape is fed as shown in FIG. 4c (when no deviation is applied by the head drive element) is shown by a broken line in FIG. 4a. _f1 , _f2
In the field, the tape is stopped, so
The head is parallel to the horizontal axis and is on the _A1 track, and the tape runs from the _f3 field to the _f6 field, and then moves onto the _A2 track. After the _f7 field, the vehicle is in a stopped state again, so the trajectory is parallel to the horizontal axis. With such a head trajectory, the signal will not be sufficiently reproduced as indicated by the dots in the head trajectory. (The two heads have the same azimuth and reproduce signals only on the A track.) Therefore, the rotary head is moved by a head drive element, but as already mentioned, the required deviation when the tape is stopped is, for example, In the f ₁ field, by giving a slope of 0 to 1 pitch as shown in Figure 4d, the head trajectory perfectly matches the A ₁ track, and in the f ₂ field the other rotating head is shown in Figure 4e. It is sufficient to give a tilt deviation of 0 to 1 pitch, as shown in FIG. In the f ₃ field, at the beginning of the f ₃ field, the track and the head trajectory match without moving the rotating head, so the deviation is set to 0, and at the end of the f ₃ field, the deviation is 1/2 pitch upward. It can be seen from Figure 4a that if allowed, it will match the _A1 track. Similarly, in the _f4 field, the other rotary head may be deflected downward by 1/2 pitch at the starting point, as shown in FIG. 4e, and set to 0 at the ending point.

Furthermore, in the f ₅ field, the pitch is shifted from 1 pitch to 1.5 pitches to match the A ₂ track, and in the f ₆ field, the pitch is shifted from 1/2 pitch to 1 pitch to match the A ₂ track. Can be done. In this way, even in the moving state, the head locus can be perfectly matched with the track, and noise-free slow playback can be achieved. The waveforms showing the amount of deviation of the rotating head (or the voltage applied to the head drive element) shown in d and e of Fig. 4 give a deviation with a slope of one track pitch in one field period when the tape is stopped. , it is shown that in the tape running state, it is sufficient to apply a deviation having an inclination of 1/2 track pitch in one field period.

In the example shown in Figure 4, the speed when the tape is moved is set to 1/2 of the standard speed, but it is not limited to this speed.If expressed generally, the speed when the tape is moved is set to 1/2 of the standard speed. If it is 1/N, then the amount by which the rotary head is deflected during tape movement is such that the track pitch inclines by (1-1/N) per field. Slow-motion playback is achieved by alternately repeating the above-mentioned stopped state and moving state, and the slow speed in this case can be set arbitrarily by changing the ratio of the stopped state and moving state, and can be achieved by continuously variable speed. You can perform slow playback. The variable speed range is from still to 1/N slow speed.

In the explanation so far, so-called field reproduction, in which reproduction is performed using rotary heads 5 and 6 having the same azimuth angle, has been explained. Needless to say, frame slow playback without noise is also possible.

FIG. 5 is a block diagram showing the main parts of an embodiment for realizing the above-described slow motion reproduction method.
In order to perform correct slow playback, the tape running and stopping points are controlled based on the position of the magnetic tape and the position of the rotary head, and the movement of the rotary head in the longitudinal direction of the drum shaft is also controlled. The rotating body 2' rotated by the rotating drum motor 16 includes driving elements 7 and 8 made of bimorph piezoelectric elements.
A drum pulse generator 17 provides a head switch signal for switching between the rotary heads 5 and 6.

To perform slow playback, repeat the operation of feeding the magnetic tape 11 when n drum pulses occur and stopping it with the next control signal (played from the control track on the magnetic tape by the control head 15). good. Therefore, the drum pulses from the drum pulse generator 17 are applied to the monostable multivibrator 18 and the monostable multivibrator 18
By setting the time constant appropriately, an output pulse is generated when n drum pulses arrive, which sets the flip-flop circuit 19. The flip-flop circuit 19 is reset by the control signal from the control head 15, and as a result, a pulse corresponding to the period from the output pulse of the mono multivibrator 18 to the arrival of the control pulse is output to the flip-flop circuit 19.
You get the output of This power is amplified by the motor drive circuit 20 and drives the capstan 14. In this case, the rotation speed of the capstan 14 is set to about 1/2 to 1/4 of the standard speed. Therefore, the capstan motor 14 moves the magnetic tape 11 by one frame using a pinch roller (not shown), and stops when the control head 15 reproduces the control signal. A flip-flop circuit 19 that determines the period during which the magnetic tape 11 is moved.
The output signal is also applied to the drive signal generator 21,
The drive signals applied to the drive elements 7 and 8 are controlled so as to give a different slope deviation during the movement of the magnetic tape than when the magnetic tape is stopped.

Incidentally, when the tape is stopped, the drive signal generator 21 generates a field-by-field gradient wave using drum pulses, and applies this to the drive elements 7 and 8. The generation of a gradient wave can be easily achieved, for example, by controlling the charging and discharging of a capacitor by a constant current source using a head switch signal. In addition,
During slow playback, control head 15
Since the control signals reproduced by the magnetic tape 11 are reproduced while the magnetic tape 11 is moving at a predetermined speed, a conventional control head is sufficient even at very slow slow speeds (for example, frame-by-frame forwarding). With this extremely simple configuration, slow playback without noise bars can be achieved.

In the embodiment shown in Fig. 5 and the explanation using the tape pattern shown in Fig. 2, the single-time mode was explained, but for example, long-time recording in which the tape speed during recording is reduced to 1/2 or 1/3 is recorded. In mode, the track pitch becomes 1/2 and 1/3. Therefore, if the same recording head is used to record, for example, a track pattern at normal speed will result in a guard band between the tracks. Even in such a case, in the present invention, the same reproducing head can be used because the reproducing head is moved so as to be placed over the recorded track. In other words, it is possible to support multiple time modes without increasing the number of heads.
However, in slow playback in time modes with different track pitches, it is necessary to switch the amplitude of the gradient wave applied to the drive element.

As described in detail above, the present invention provides a VTR that performs slow playback by moving the magnetic tape intermittently in two modes: stopped and running, by attaching a rotating head to a head drive element such as a piezoelectric element, This device performs slow-motion playback by mechanically deflecting the rotary head with an inclination in units of field periods, and when moving the tape, the inclination is controlled to change according to the moving speed. Its value is extremely high because it can produce beautiful slow and still images with no distortion, and it can also be configured on a VTR with multiple time modes without increasing the number of heads.

[Brief explanation of drawings]

FIG. 1 is a model diagram of a rotating head group used in an embodiment of the present invention, FIG. 2 is a diagram showing a recording track pattern on a magnetic tape and a scanning locus of a reproducing head, and FIGS. 3 a and b are diagrams for explaining the amount of deviation given to the rotating head, Figures 4a, b,
c, d, and e are diagrams for explaining the operation of the embodiment of the present invention, and FIG. 5 is a main part configuration diagram for explaining the implementation example of the present invention. 2... Rotating drum, 3, 4... Rotating head,
5, 6... Rotating head, 7, 8... Drive element, 1
1... Magnetic tape, 14... Capstan motor, 15... Control head, 16... Rotating drum motor, 17... Drum pulse generator, 1
8... Monostable multivibrator, 19
. . . flip-flop circuit, 20 . . . motor drive circuit, 21 . . . drive signal generator.

Claims (1)

[Claims] 1. In a video tape recorder in which a magnetic tape is intermittently moved while being switched between a stopped state and a running state at a speed lower than the standard speed during playback, a pair of rotating magnetic heads are each attached to the movable part of the head drive element, and the above-mentioned In order to provide the rotary magnetic head with a mechanical deflection adapted to the stopped state and the running state, the signal applied to the head drive element is a capstan drive signal having information as to whether the tape is in the running state or the stopped state. From the head switch signal indicating one field period, approximately 1 in one field period when the tape is stopped.
1. A slow motion reproduction method, characterized in that the tape has a slope of track pitch, and is configured to form a signal having a slope of less than one track pitch corresponding to a predetermined speed in the running state of the tape.