JPS6335151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a helical scan type video tape recorder (hereinafter referred to as VTR) in which a magnetic tape is run intermittently so that noise bars do not appear on the playback screen and the speed is continuous. The present invention relates to a slow motion playback method that makes it possible to realize slow playback and still playback that respond to changes.

Conventionally, there are two methods for slow and still playback in VTRs that do not cause noise bars to appear: The first method is to attach the rotary head to a head drive element, such as a bimorph piezoelectric element, and
The head is structured to be mechanically displaceable in a direction perpendicular to the head scanning direction, and the head is moved so as to scan a desired recorded track even if the tape speed during playback changes. In this method, the magnetic tape (hereinafter simply referred to as tape) is continuously running, and the signals given to the piezoelectric element to move the rotating head accordingly include tape speed information during playback and a playback control signal (hereinafter referred to as tape). ,
CTL), head switch signal (hereinafter referred to as
It is necessary to prepare signals with complex waveforms that correspond to all tape speeds. Especially during very slow slow playback.
Conventional VTRs cannot play CTL,
Special measures must be taken to counter this. As described above, the first method allows noise-free slow and still playback, but on the other hand, it has the disadvantage that it results in an extremely expensive VTR.

The second method is to drive the tape during playback intermittently with two modes: tape running state and tape stop, and obtain a playback signal with a playback head that has a track width wider than the recording track width, thereby achieving an arbitrary slow ratio. This is to realize the following.

However, this method requires the use of a playback head whose track width is necessarily larger than the recording track width, which may not be a major obstacle for single-time mode VTRs, but for multi-time mode VTRs. , a head with a track width corresponding to the number of time modes must be prepared.
For example, a VTR that can record and play back 2, 4, and 6 hours on the same tape must have three sets (six) of rotating heads to achieve slow playback without noise bars in all time modes. I can't.

In addition, in VTRs that can achieve slow motion playback using this intermittent drive method, the running speed of the tape cannot be ideally driven due to the inertia of the capstan motor, etc., and the tape tension changes due to temperature changes. In principle, variations in running speed between drives occur due to external changes, and these variations directly lead to excitation of the reproduced signal, which is a drawback.

The present invention aims to eliminate the drawbacks of the conventional slow motion playback methods as described above, and provides a multi-time mode using relatively simple means.
Compatible with VTRs, and even when the tape running speed changes continuously during movement, or when the running speed varies between drives, the playback signal does not deteriorate and the slow and still images are always beautiful. This method provides a method that enables playback, in which the tape is run intermittently, a pair of rotating heads are each attached to a head drive element, and when the tape is stopped, the tape tilts by one pitch in one field period. The main idea is to apply the displacement obtained by combining the above displacement with the displacement based on the tape movement distance information to the rotary head in the tape running state.

Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 shows a model of a tape pattern recorded on a tape and a group of rotating heads. In the figure, four rotating heads are mounted on a rotating drum 2 driven by a motor 1. That is, numerals 3 and 4 are rotary heads for recording and reproducing having different azimuth angles, and are fixed on the rotary drum 2 at a position of 180 degrees. In addition, 5 and 6 are rotary heads dedicated to reproduction with the same azimuth angle.
Its azimuth angle coincides with the azimuth angle of either of the rotating heads 3, 4. The rotary heads 5 and 6 are driven by a head drive element 7 such as a piezoelectric element.
and 8, and each rotary head can be moved in the vertical direction by the head drive elements 7 and 8. Also shown on the tape 9 are a head scanning direction, a tape running direction, and recording tracks A ₁ , B ₁ , A ₂ , B ₂ . Here, A ₁ , A ₂ , A ₃ ... are tracks recorded by a rotating head with the same azimuth, for example, rotating head 3, and B ₁ , B ₂ , B ₃ , ... are tracks recorded by a rotating head with a different azimuth angle. , for example, a track recorded by the rotary head 4.

Now, in the still mode in which the tape 9 is stopped during playback, the travel trajectory of the playback head is shifted by one track pitch, as shown by the broken line 10 in FIG. At this time, for example, the _A1 track, that is, the rotary head 5 having the same azimuth as the rotary head 3.
When played back, the signal that is played back is only the shaded area, and the signal is missing in the upper part of the figure.
Therefore, in order to reproduce all of track A ₁ even when the tape is stopped, it is only necessary to scan while moving the rotary head one pitch in the direction perpendicular to the head scan during one field in which the rotary head 5 contacts the tape. . Further, by applying a similar displacement to the rotary head 6 that comes into contact with the tape in the next field, the tracks _A1 are alternately scanned, and field still playback without noise can be realized. This can be done by displacing the rotary heads 5 and 6 having the same azimuth by applying a drive voltage of an appropriate waveform to the head drive elements 7 and 8. In this case, the applied drive voltage is expressed on the horizontal axis. Figure 2 a and b show the time taken.
It can be seen that this may be a triangular wave voltage having a period of 2 fields. In FIG. 2, the rotary head is not in contact with the tape in the section indicated by the broken line, and the waveform may not be the one shown.

Next, slow motion playback will be explained.
In this case, for convenience of explanation, the tracking state description method shown in FIG. 3 will be used. The horizontal axis in FIG. 3 indicates time, and the HSW in FIG. 3b, which is a 30 Hz rectangular wave, is considered as a reference, and a field number is written for each field. The vertical axis indicates the amount of tape movement and also indicates the track width and head width. Therefore, A ₁ repeats the track A ₁ in the tape pattern of FIG. 1, and the same applies to B ₁ . When the tape is played back at normal speed (same speed as when recording), the tape is advanced one pitch during one field period, so the trajectory of the playback head at that time is at a 45° angle in the figure, and the playback head The tracks to be processed are A ₁ , B ₁ ,
The order is A ₂ , B ₂ , A ₃ , ..., and normal playback occurs.

Next, in a still state, the tape does not move as time passes, so the trajectory is horizontal to the horizontal axis. If the track width and head width are the same, only half of each track signal will be reproduced, and noise bars will appear on the screen. Therefore, in a VTR with a structure in which a rotating head is mounted on a head driving element, if a triangular wave-like displacement as shown in Figure 2a and b is applied to the head driving element, the rotating head and track can be perfectly aligned. Therefore, it can be easily understood from FIG. 3a that still reproduction without noise can be realized on the screen.

Now, regarding slow motion playback, the tape is fed intermittently in synchronization with the HSW, and stops after moving two tracks. Now, suppose that the tape feeding speed is increased to 1/2 as shown in FIG. 3c, for example. An example of the head trajectory at this time (when no displacement is applied to the head drive element) is shown by the broken line A in FIG. 3A. Fields ₁ and ₂ are fields where the tape is stopped on the _A1 track, so the head trajectory is parallel to the horizontal axis. field ₃ ,
₄ , ₅ , _{and 6} are periods in which the tape is fed at 1/2 speed and moves two tracks, and after ₇ , it stops again. Here, when moving the tape, a displacement corresponding to the tape movement distance is given to the playback rotation head in the opposite direction based on the tape movement distance information, so that the playback rotation head trajectory scans the same trajectory as at the start of tape movement. This is shown by the dotted line B in Figure 3.

An example of the output from the tape movement distance information is shown in FIG. 3d. In tape stop fields ₁ and ₂ , the displacement is O, but as the tape moves from ₃ , the displacement increases; for example, at the start of ₄ , it is 1/2 pitch,
1 pitch at the start of ₅ , 1 pitch at the start of ₆
The displacement is 1.5 pitches, and it can be seen that this corresponds in an inverse relationship to the broken line A in FIG. 3A. Therefore, if this displacement is applied to the head drive element, the playback rotating head will maintain a constant position relative to the tape even when the tape is moving, and its trajectory will be as shown in Figure 3a.
As shown in the dotted line B. This is ₁ to ₆
This indicates that the position of the reproducing rotary head with respect to the tape has not changed until then. That is, at the end of ₆ , even though the tape has moved 2 tracks from the ₃ starting point, the reproducing rotary head is displaced so as to scan the previous track _A1 . Therefore, by canceling the displacement and setting it to O at the same time as ₇ starts, the regenerating rotary head will match the locus shown by the broken line A in Figure 3a, and this will be changed to ₇ , ₈ , It is shown in dotted line B in ₉ .

Now, by applying the triangular wave-shaped displacement shown in FIG. 2 when the tape is stopped to the reproducing rotary head which has been given a displacement based on the tape movement distance information described above, the reproducing rotary head can always record data even when the tape is moving. It will match the track.
The locus of the reproducing rotary head at this time is shown by diagonal lines in FIG. 3a. You can see that ₁ to ₆ match the _A1 track, and ₇ and onwards match the _A2 track.

Now, the tape movement distance information is obtained by accurately detecting the movement distance by counting the output pulses (hereinafter referred to as FG) from a frequency generator that generates pulses proportional to the tape movement speed, and according to the counted number. It will be stated that the tape movement speed is not an issue because the output is the displacement that was generated. In the above explanation, the tape feed was taken at 1/2 speed as an example, but
In an actual VTR, the feed speed changes continuously due to the inertia of the capstan motor, and some variation occurs with each drive. However, in the present invention, even if the tape speed during tape movement changes continuously or varies from drive to drive, the playback head is given a displacement corresponding to the change, so the above-mentioned sloppiness can be avoided. This is not a problem and is shown in FIG. b in Figure 4 is
HSW is shown, and c shows the tape speed, and the tape continuously changes from O to normal speed when the tape moves. At this time, the trajectory of the reproducing head in a state where no displacement is applied to the head driving element becomes a curve as shown by the broken line A in FIG. 4A. The output of the tape movement distance information at this time is shown in FIG. 4d, and the locus of the reproducing rotary head when the displacement is applied to the tape drive element is shown by the dotted line B in FIG. 4a. Looking at this, it can be seen that the change in speed has been absorbed and the trajectory is the same as that shown by the dotted line B in FIG. 3A. Therefore, at this time, by further applying the triangular wave-like displacement shown in FIG. 2 to the reproducing rotating head,
It is easy to understand that the reproducing rotary head and the track coincide, and the locus of the reproducing rotary head at this time is as shown by diagonal lines in FIG. 4a.

FIG. 5 is a diagram showing an example of the main circuit configuration for realizing the slow motion reproduction method based on the present invention described above. In the figure, a triangular wave generating circuit 12 receives the HSW from the VTR 11 and generates a triangular wave having a displacement of one pitch per field as shown in FIG. The tape movement distance detection circuit 13 includes a counter 14 and a D/A (digital/analog) conversion circuit 15. The counter 14 inputs the FG from the VTR 11 and a drive pulse (hereinafter referred to as DP) that outputs an "H level" signal in the tape movement field. (for example, the maximum value of the counter). The D/A conversion circuit 15 has a counter 14
It converts the digital signal that is the output of the circuit into an analog quantity, such as a ladder resistor. Then, by adding the output of the tape movement distance detection circuit 13 and the output of the triangular wave generation circuit 12 in an adder 17 and applying the result to the head drive element 16, noiseless slow playback can be realized.

Next, each operation will be explained based on the time chart shown in FIG. In FIG. 6, a is HSW, b is DP indicating a tape movement field, and c is FG, which correspond to the respective symbols in FIG. 5, respectively. The output of the counter 14 is D/A converted by the D/A conversion circuit 15.
The converted output is d in FIG. This waveform d is preset so that FG occurs from movement start field ₃ , the displacement increases as it counts down, the displacement reaches a maximum of 2 pitches just before stop field ₇ , and the displacement becomes O at ₇ . It shows that Further, e in FIG. 6 is one output of the above-mentioned triangular wave generation circuit 12, and this waveform e and the above-mentioned waveform d
The waveform f shown in FIG. In other words, by applying a voltage with a waveform of f to the head driving element, the reproducing rotating head and the track are perfectly aligned.
Beautiful slow playback without noise can be achieved.

Here, f varies greatly between ₆ and ₇ , which may adversely affect the head scanning of ₇ due to ringing of the head drive element. Therefore, since the part indicated by the broken line is the period in which the reproducing rotating head is not in contact with the tape, it does not matter what waveform is given to it, so for example, as shown in Figure _6g , the displacement is set to By eliminating the sudden change between ₆ and ₇ , ₇
Head scanning can be performed smoothly.

As is clear from the above description, the present invention provides a VTR that drives a tape intermittently, in which a rotary head is attached to a movable part of a head drive element such as a bimorph piezoelectric element, and when the tape is stopped, the tilt is tilted by one pitch in one field period. When the tape is moving, a displacement obtained by combining the displacement based on the tape movement distance information with the displacement when the tape is stopped is applied to the rotating head. Even when the tape continues to change speed, the playback rotating head and track perfectly match, ensuring stable, noise-free, beautiful slow and still playback.
Moreover, it can be realized even in a VTR having multiple time modes without increasing the number of rotating heads, and its value is extremely high.

[Brief explanation of the drawing]

Figure 1 is a model diagram showing the tape pattern azimuthally recorded on the tape and the rotating head group.
Fig. 2 is a diagram showing the amount of displacement applied to the rotating head, Figs. 3 and 4 are diagrams for explaining slow motion reproduction, and Fig. 5 is a main block diagram for explaining an embodiment of the present invention. The configuration diagram and FIG. 6 are timing charts of signals of each part in FIG. 5. 2... Rotating drum, 3, 4, 5, 6... Rotating head, 7, 8... Head driving element, 9... Magnetic tape, 11... VTR, 12... Triangular wave generation circuit,
13...Tape movement distance detection circuit, 14...Counter, 15...D/A conversion circuit, 16...Head drive element, 17...Adder.

Claims (1)

[Claims] 1. During variable speed playback of a video tape recorder, the magnetic tape is moved while being switched between a stopped state and a running state during playback, and a pair of rotary heads are respectively attached to the movable parts of the head drive elements, and the magnetic tape is moved while being switched between a stopped state and a running state. When the tape is stopped, a displacement having an inclination of one pitch is applied to the rotary head in one field period, and when the tape is running, a frequency generator generates a pulse number proportional to the running speed in response to the displacement when the tape is stopped. 1. A slow motion reproduction method, characterized in that a displacement obtained by composing displacements based on obtained tape movement distance information is applied to the rotary head. 2. In the description of claim 1, the tape movement distance information is obtained by using a counter that receives pulses from the frequency generator and performs a reset or preset operation in a tape stop field, and a digital-analog method for converting the output of the counter. 1. A slow motion reproduction method, characterized in that the slow motion is obtained using a D/A conversion circuit.