JPS6335152B2 - - 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 that responds to changes and still playback.

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 of resulting 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 always wider than the recording track width, and while this may not be a major obstacle for a single-time mode VTR, it is a problem for a multi-time mode VTR. 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 a VTR that achieves slow playback using this intermittent drive method, the positional relationship between the rotating head and the recording track on the tape when the tape stops is
It is necessary that the tape stop position be constant at all times, and therefore extremely high precision is required for the tape stop position, which requires a complex and expensive circuit configuration. In addition, even in the above circuit configuration, some variation in tape stop position will occur in principle due to various external changes such as changes in tape tension due to temperature changes, and this variation will directly lead to deterioration of the reproduced signal. There were flaws.

The present invention aims to eliminate the drawbacks of conventional slow-motion playback as described above, and provides a multi-time mode using relatively simple means.
It provides a method that is compatible with VTRs and allows beautiful slow and still playback without deteriorating the playback signal even when the stop position varies, and allows the tape to run intermittently and The main idea is to attach a pair of rotating heads to each head drive element, and to give the head drive element a swing waveform that takes into account the amount of displacement according to the tape running speed and the amount of displacement based on tape stop position information. be.

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, tape 9
, the head scanning direction, tape running direction, recording tracks A ₁ , B ₁ , A ₂ , B ₂ . . . are shown. 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 with a rotating head with a different azimuth angle. These are tracks recorded by a head, for example a rotary head 4.

Now, in the still mode in which the tape 9 is stopped during playback, the scanning locus 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 shows the amount of tape movement and also shows 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 an angle of 45° 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 over time, so the horizontal axis represents a horizontal trajectory. 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 driving element) is shown by a broken line in FIG. 3a. Fields f ₁ and f ₂ are fields where the tape is stopped on the A ₁ track, so the head locus is parallel to the horizontal axis. Field f ₃ , f ₄ ,
At _f5 and _f6 , the tape is fed at 1/2 speed and moves two tracks, and at _f7 , it is stopped again.
In the case of such a trajectory, the signal reproduces only the dotted portion in FIG. 3a. Therefore, the rotary head is moved using a head drive element, but when the tape is stopped, for example in field _f1 , by giving a slope of 0 to 1 pitch as shown in Figure 3d, the head trajectory is completely matches A ₁ track. In addition, in field f ₃ during movement, the head trajectory and track match at the beginning of the field, so the deviation can be 0, and at the end of f ₃ , if it is displaced 1/2 pitch upwards, A ₁ It can be seen that it matches the track. Similarly, by applying the displacement shown in FIG. 3e to the other rotating heads, the head locus and track will perfectly match both when the tape is stopped and when the tape is moving, and slow playback without noise can be realized. Also, in the above example, the tape feed speed was 1/2 times the normal speed, but this may be 1/4 times the speed, 1/3 times the normal speed, etc. Needless to say, the amount of displacement to be applied needs to be set according to each speed.

In such a slow motion playback device that drives the tape intermittently, it is necessary that the positional relationship between the playback head and the track is always constant when the tape is stopped. That is, in FIG. 3a, the positional relationship between the reproducing rotary head and _{A1 track at f 1 and} f ₂ and the positional relationship between the reproducing rotary head and A ₂ track at f ₇ and f ₈ are constant. This is a prerequisite for realizing this system. However, due to various external changes such as changes in tape tension due to temperature changes, some variation in the tape stop position generally occurs.
Therefore, the head trajectory when there is variation is shown by a broken line in FIG. 4a using the tracking state description method. However, the feed speed is set to 1/2 speed, and the head is not driven. Looking at Figure 4a, we can see the positional relationship between the reproducing rotary head and the _A1 track at _f1 and _f2 .
It can be seen that the positional relationship between the reproduction rotary head and the _A2 track at _f7 and _f8 is misaligned. That is,
This shows when the tape is fed two tracks at f ₃ , f ₄ , f ₅ , and f ₆ , but the stop position is shifted and the tape is fed more than 2 tracks, and the field after f ₇ advances a little too far and stops. .

Now, in this state, if displacement amounts as shown in Fig. 4b and c are applied to both reproducing rotary heads, the fourth
The portion shown by the dots (matte texture) _{in FIG} . The signal reduction portion is denoted by s.

Therefore, in the field after f ₇ , by applying drive voltages with the waveforms shown in Figure 4 d and e, which also take into account the tape stop position, to both head drive elements, the field after f ₇ is also connected to the playback rotating head and the track. can be perfectly matched.

Next, a method for detecting the tape stop position will be described. One control pulse (CTL) is recorded on every two tracks of the tape, and these pulses are regularly recorded with a constant phase with the tracks recorded on the tape. Therefore, by using this CTL as a reference and measuring the amount of tape movement from that reference until the tape stops, it is possible to accurately know the tape stop position. Here, the amount of tape movement can be realized by counting output pulses (hereinafter referred to as FG) from a frequency generator that generates pulses proportional to the number of rotations of a capstan for driving tape running. In other words, the variation in the tape stop position can be detected by counting the FG from CTL to the tape stop as a reference, and detecting it as a change in the count.The deviation based on this count can be detected by the head drive element. By adding
The rotary head can be deflected to accommodate variations in tape stop position. In addition, the fourth
m in the figure represents the amount of stop position deviation.

FIG. 5 is a block diagram of essential parts for realizing the above-described slow motion reproduction method. In the same figure, the triangular wave generation circuit 12 is connected to the VTR 11.
drive pulse (hereinafter referred to as DP) without outputting an “H level” signal in the tape movement field.
This is a circuit which receives a triangular wave as an input and generates a triangular wave with one pitch per field when still, and with a deviation commensurate with the moving speed when moving, as shown in FIGS. 3d and 3e. The tape stop position detection circuit 13 is
It receives CTL, FG, and DP from the VTR 11 as input, and generates a voltage based on the tape stop position. A signal obtained by adding the output of the triangular wave generation circuit 12 and the output of the tape stop position detection circuit 13 in an adder 14 is supplied to the head drive element of the VTR 11.

FIG. 6 is a diagram showing an example of the configuration of the tape stop position detection circuit 13. In the same figure, the counter 15 is, for example, a 4-bit down counter, and counts down the FG from the VTR 11 in FIG.
Preset with CTL (e.g. to maximum value of counter)
It is something to do. The D/A conversion circuit 16 is, for example, a ladder resistor, and easily converts a 4-bit digital signal into an analog quantity. The sample and hold circuit 17 determines the timing of applying the output of the D/A conversion circuit 16 to the head drive element, and includes an analog switch 18, a capacitor 19, and an operational amplifier 20. controlled by Here, each operation will be explained based on the time chart shown in FIG. a in Figure 7 is shown in Figure 5.
HSW from VTR 11, b is DP indicating the tape movement period, c is FG, d is CTL, e is the output of D/A conversion circuit 16, and it goes down as FG occurs during tape movement from field _f3. count and
This shows that it has been preset to the maximum value by CTL and has continued to count down again since then. Also, the seventh
In the figure, f shows the output of the sample and hold circuit 3. During the period when DP of b is at "H level", it continues to hold the previous value, and the field where the tape has stopped shows that it is being sampled. It shows.
The difference in level between f ₆ and f ₇ indicates that the positional relationship between the reproduction rotary head and the track has changed between the field before f ₂ and the field after f ₇ . g is one output of the triangular wave generating circuit 12 in FIG. 5, and the sum of this g and the waveform f is h, that is, the output of the adder 14 in FIG. 5, which is the waveform itself given to the head drive element. be.

Here, FIG. 7f, g, and h will be explained in more detail. The fact that the potential drops between _f6 and _f7 at f indicates that the number of FGs from CTL to tape stop was greater than before _f2 . That is, the positional relationship between the track and the reproducing rotary head when the tape was stopped shows that after _f7 , the tape stopped in a direction slightly further forward than before _f2 . Therefore, for the field after _f7 , it is necessary to shift the waveform that has been applied to the drive element a little downward. This is shown in FIG. 7h, and by applying this swing waveform to the head drive element, the reproducing rotating head and the track are perfectly aligned. This means that the fourth
This means that any correction between the reproduction rotation head and the track of the f ₇ , f ₈ , and f ₉ fields in Figure A has been realized in a circuit, and the swing wave determination of f ₇ , f ₈ , and f ₉ has been shifted downward. It is clear then that the regeneration rotary head and the track match perfectly.

FIG. 8 is a diagram showing another example of the configuration of the tape stop position detection circuit 13. While the configuration of the sample and hold circuit 17 in FIG. 6 includes an operational amplifier 20 that handles analog quantities,
In the figure, only the latch circuit 22 that handles digital quantities is replaced, and since the basic circuit configuration and operation are essentially the same as those in FIG. 6, a description thereof will be omitted here.

Furthermore, due to the configuration in which the tape stop position detection circuit 13 counts FG, it is clear that the tape always either advances in the forward direction or stops, and that it should never be reversed. be. However, it is possible to detect when the tape is reversed by using a two-phase FG, for example, and by switching the down counter to an up counter at that time, the tape stop position detection circuit can be used even when the tape is reversed. works fine.

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 one pitch in one field period. This system performs slow motion playback by applying a displacement to the rotary head that has an inclination that corresponds to the running speed when in motion, and is particularly effective in reducing variations in the tape stop position that occur when the tape is driven intermittently. , the amount of displacement based on the tape stop position information is absorbed by applying it to the rotating head, and beautiful slow and still playback without noise is always achieved stably, and even in VTRs with multiple time modes, the number of rotating heads can be reduced. This can be achieved without increasing the amount of energy, 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. 6 is a diagram showing a configuration example of the tape stop position detection circuit, FIG. 7 is a timing chart of the signals of each part in FIGS. 5 and 6, and FIG. 8 is a diagram showing an example of the configuration of the tape stop position detection circuit. It is a figure showing an example of composition. 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 stop position detection circuit, 14... Adder, 15... Counter, 16... D/A conversion circuit, 17... Sample hold circuit, 22... Latch circuit.

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 rotating magnetic heads are each attached to a movable part of a head drive element, When the tape is stopped, a deviation having an inclination of one pitch is applied to the rotating magnetic head in one field period, and when the tape is running, a deviation having an inclination corresponding to the running speed is applied to the rotating magnetic head. The video tape recorder is characterized in that a displacement amount is applied to the rotating magnetic head based on tape stop position information indicating the positional relationship between the track recorded on the magnetic tape and the rotating magnetic head when the tape is stopped. A slow motion playback method. 2. In the description of claim 1, the tape stop position information includes the output of a frequency generator that generates a number of pulses proportional to the tape speed and the control pulses recorded on the control track on the magnetic tape. A slow motion reproduction method characterized by using the method. 3. In the statement of claim 1, the tape stop position information is a counter that receives output pulses from a frequency generator that generates a number of pulses proportional to the tape speed and that is reset or preset by control pulses; The slow motion is obtained from a circuit including a D/A conversion circuit that converts the output of the counter from digital to analog, and a sample hold circuit that samples and holds the output from the D/A conversion circuit. How to play. 4. In the statement of claim 1, the tape stop position information includes a counter that receives output pulses from a frequency generator that generates a number of pulses proportional to the tape speed and is reset or preset by control pulses; A slow motion reproduction method characterized in that the output is obtained from a circuit including a latch circuit that latches the output of the counter and a D/A conversion circuit that converts the output of the latch circuit from digital to analog.