JPH042039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable speed playback device for a helical scan video tape recorder (VTR).

[Conventional technology]

In the two-head helical scan method, when displacing the rotating magnetic head in the direction of the rotation axis using an electromechanical transducer such as a piezoelectric bimorph to obtain a variable speed reproduction image without noise bars,
During the period when the rotating magnetic head is not scanning the tape (non-scanning period), its position is moved,
The next time you start scanning across the tape, you need to make sure you are in the correct position. Conventionally, for this purpose, a rotating magnetic head is moved from the head position at the end of a scan to the position at the start of the next scan.
A method has been implemented in which the head is gradually displaced during the period when the tape is not being scanned (non-scanning period).

[Problem to be solved by the invention]

However, in the conventional technology described above, the direction of displacement required of the head is generally different between the period when the head is scanning the tape (scanning period) and the period when the tape is not being scanned (non-scanning period). Because it is in the opposite direction, the conventional method requires an abrupt change in direction near the end of this non-scanning period. Further, when changing the displacement method according to various modes of variable speed playback, such as forward rotation slow, forward rotation search, reverse rotation slow, and reverse rotation search, it is necessary to make complicated displacements as a head.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video tape recorder in which the head correctly scans the recording track even when the head starts scanning the tape, and can easily apply the necessary displacement to the head in accordance with the variable speed playback mode. do.

[Means to solve the problem]

To achieve the above object, the present invention provides a rotating magnetic head with a displacement of twice or approximately twice the track pitch at a point on the tape at or near the end of the scan, and within a non-scanning period. The displacement is controlled so that it decreases linearly or approximately linearly with the passage of time, and the rotating magnetic head reaches the scanning start point at the same or substantially the same displacement speed as the displacement speed during the scanning period and smoothly moves to the next position. to start scanning. To this end, the present invention includes: (a) electromechanical transducers (corresponding embodiment codes 6 and 7) that independently displace the rotating magnetic head (corresponding embodiment codes 4 and 5) for each channel; ) A sawtooth wave generation circuit for still playback (corresponding embodiment codes 8, 9,
10) and (c) a sawtooth wave generation circuit for slow reproduction that generates a sawtooth wave voltage with a period that is an integral multiple of the rotation period of the rotating magnetic head (corresponding embodiment codes 13, 14, 1).
6); (d) an adder (corresponding embodiment code 19) for adding the output of the sawtooth wave generation circuit for still reproduction and the output of the sawtooth wave generation circuit for slow reproduction; and (e) a drive amplifier that drives an electromechanical transducer based on the output of the adder; It has a configuration that is controlled so that.

[Effect]

The electromechanical transducer has a rotating magnetic head mounted thereon, and is deformed and displaced by a predetermined amount by receiving a drive displacement input from a drive amplifier, thereby imparting a moving displacement to the rotating magnetic head.

The sawtooth wave generation circuit for still reproduction generates a sawtooth wave voltage corresponding to the still mode for applying the electromechanical transducer to the rotating magnetic head with a displacement amplitude twice or approximately twice the track pitch.

The sawtooth wave generation circuit for slow reproduction generates a sawtooth wave voltage corresponding to the slow mode with a period that is an integral multiple of the rotation period of the rotating magnetic head.

The adder adds the output of the sawtooth wave generation circuit for still reproduction and the output of the sawtooth wave generation circuit for slow reproduction. The added output is transmitted to the drive amplifier side.

The drive amplifier drives the electromechanical transducer with the output based on the output of the adder.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 to 5. FIG. 1 shows the arrangement of a rotating magnetic head (hereinafter simply referred to as a head) in a rotating cylinder.
2 to 4 show the time course of the head displacement during the variable speed playback mode. FIG. 5 shows a block diagram of the regeneration circuit for the variable speed regeneration mode.

FIG. 1 shows a head layout diagram of an embodiment of the present invention in a so-called two-head azimuth type helical scan VTR. 1 and 2 are recorded at normal speed,
These heads are configured to have different azimuth angles from each other and are fixed to a rotating cylinder 3. Dedicated heads 4 and 5 for variable speed playback mode are fixed to the free ends of cantilevered piezoelectric bimorphs 6 and 7, respectively, and have the same azimuth angle as either head 1 or 2. Has horns. When a control voltage is applied to the piezoelectric bimorphs 6 and 7, the heads 4 and 5 are displaced in a direction perpendicular to the plane of the paper, that is, in the direction of the rotation axis of the rotary cylinder 3, and this causes deviation of the heads from the recording track during variable speed playback. Correct. The heads 1, 2 and 4, 5 are each at the same height in the direction of the rotation axis, and their positions are adjusted so that they form an angular interval of 180° from each other.

FIG. 2 is a diagram explaining the principle of displacing the rotating magnetic head in the direction of the rotation axis in the apparatus of the present invention, in which the tape running direction is the same as the recording direction;
That is, it shows the temporal change in the amount of displacement of the rotating magnetic head in the so-called forward rotation search mode, in which the running speed is higher than the normal speed in the forward direction.
In general, in the case of variable speed playback at n times the normal speed, when running in reverse, n is set to a negative value, and the displacement in the rotational axis direction to be applied to the head is on average (n-1) times the track pitch P per field. be. Furthermore, when the head 4 finishes scanning the tape, the position that the head 5 should take for the next tape scan is an odd multiple of the track pitch P, if these heads have the same azimuth angle. The height is shifted from 4. Therefore, in variable speed reproduction of n times speed, when n is an even number, n-1 becomes an odd number, and from the above relationship, it is possible to correct the average deviation in one field period. For this reason,
The heads 4 and 5 only need to repeat the same axial displacement (sawtooth shape) during each tape scanning period. The required head displacement in this case is shown in FIGS. 2a and 2b.

In FIG. 2, the horizontal axis shows time, the vertical axis shows displacement, and the solid line shows the amount of displacement required during the period when the tape is scanned. In FIG. 2, for example, if the displacement shown in b is the required displacement for the head 4, then the displacement shown in b is the required displacement for the head 5. As shown in the figure, the required displacement is a displacement that varies linearly with time during one field period, and this is due to the scanning trajectory of the head on the tape during recording, and
This occurs because the directions of the scanning trajectories on the tape during variable speed playback do not match. head 4,
In principle, any displacement is allowed during the so-called non-scanning period when 5 is not scanning the tape, but in reality, the next time the tape is scanned, it is possible to start scanning smoothly and without causing ringing or the like in the displacement waveform. It is required that there be no. Figures 2c and d show the displacements to be applied to the head. c shows the displacement waveform of head 4, and d shows the displacement waveform of head 5. The waveforms of the solid line portions in FIGS. 2c and d are the same as the waveforms in FIGS. 2a and b, respectively. The broken line portion shows the displacement waveform of the head during a period when the head is not scanning the tape. As is clear from the figure, the point at which the head finishes scanning the tape (actually, it is the point at which the playback section ends, but for ease of understanding,
Assuming that these match, a displacement that is twice the amount required to move to the next position to start scanning ((n-1)P in the figure) is instantaneously generated,
Thereafter, it attenuates while making a linear displacement with respect to time, and reaches the displacement at the start of scanning. This means that the heads 4 and 5 are moving at the same speed during the tape non-scanning period as during the scanning period. In this way, as is clear from the figure, tape scanning can be started extremely smoothly. Further, the displacement waveform shown in the figure is a sawtooth waveform with a period of 2 fields, and is a waveform that can be created extremely easily. Since the head undergoes a rapid positional change at the end of scanning, there is a concern that ringing may occur in the head displacement due to bimorph resonance, etc., but this can be fixed by using an appropriate low-pass filter as described later. This can be prevented by applying a waveform with this portion blunted to the bimorph drive amplifier. Furthermore, even if some ringing occurs, the part of this sudden change is positioned farthest from the next scanning point, so the ringing will attenuate and converge within this non-scanning period. It is easy to do. Also, the use of a dynamic range that is twice the required displacement between the scan end point and the scan start point becomes a problem in high-speed search mode, but in this case, the countermeasures described below should be taken. By applying this, it is possible to prevent an increase in dynamic cleansing. In the above example, the search was described for an even numbered speed, but in the case of an odd numbered speed, if a DC voltage is applied to the bimorph to create a step equal to one track pitch, the head step required when switching heads will be equal to the track pitch. It is an even number multiple, and can be handled in exactly the same way as the above method.

Next, an embodiment of the present invention in slow playback will be described. An embodiment of the present invention will be described below, taking as an example the case of 1/2 speed slow playback mode of forward running.

3a and 3b show time-lapse waveforms of head displacement in the 1/2 slow playback mode of the present invention. Third
In Figures a and b, as in Figures 2c and d, solid lines indicate displacement during the tape scanning period, and broken lines indicate displacement during the tape non-scanning period. a is the displacement of the head 4, and b is the displacement of the head 5. The period of change in displacement is 4 fields. As is clear from the figure, even during the tape non-scanning period, the head moves at the same speed and in the same direction as during tape scanning. Therefore, signal waveforms as shown in Fig. 3a and b are generated by a reproduction circuit using the head switching signal as a reference.
By applying this waveform to the drive amplifiers of the bimorphs 6 and 7 to displace the bimorphs, variable speed playback in 1/2 slow mode in a noise barless state is realized. This method is applicable not only to the 1/2 slow mode described above but also to other slow mode speeds. Next, a means for creating a signal waveform during slow motion will be explained. The limit of slow playback by slowing down the playback tape speed is still playback, so conversely, slow playback can be considered as an extension of still playback. Therefore, the displacement required during slow playback can be given as the sum of the displacement required during still playback and the additional displacement required during slow playback.

FIGS. 3c and 3d show displacement waveforms necessary for heads 4 and 5 to perform still reproduction according to the present invention, respectively. In this embodiment, the period is 2 fields, and the head shift amount at the end of scanning is 2 track pitches, resulting in a sawtooth waveform as shown in the figure. As in the example shown in Fig. 2 above, by quickly performing a shift operation twice the head shift amount required during the non-scanning period at the end of scanning, the head can be moved at the same speed as the scanning period even during the non-scanning period. The scanning start point can be smoothly reached. 3e and f are additional displacements for slow playback.
In 1/2 throw, the track deviation amount is 1/2 track pitch per field, so
A difference of two track pitches will occur in four fields. Therefore, it is desirable to perform a head shift of two track pitches every four fields. The displacement waveforms are the waveforms shown in e and f. As is clear from the above explanation, this waveform shifts by 2 track pitches every 8 fields in 1/4 slow mode, and by 2 track pitches every 16 fields in 1/8 slow mode. It's a good thing.

In other words, when m is any natural number, 1/m
In slow mode, it is enough to shift 2 track pitches every 2m field. Since the rotation period of the rotating magnetic head is 2 fields, a shift of 2 track pitches is performed every m times the rotation period.

By adding waveforms c and e, waveform a
Waveform b can be obtained by adding waveforms d and f.

Note that the center positions of waveforms e and f are shifted, but this shift amount is a constant value, and it is sufficient to add a constant DC voltage in a reproducing circuit, or to add an auto-tracking operation as described later. When a reproducing circuit is used, this deviation is automatically corrected, so there is no problem in practice.

FIG. 4 shows an embodiment in the 1/4 slow mode of correction. A to f in FIG. 4 correspond to a to f in FIG. 3, respectively, and a and b in FIG.
Displacement waveforms of heads 4 and 5 during 1/4 slow mode; c and d are displacement waveforms during still playback as in Figure 3; e and f are additional displacements for 1/4 slow mode playback. The waveform a is obtained by adding the waveform c and the waveform e, and the waveform b is obtained by adding the waveform d and the waveform f. The above has described forward rotation (forward) search and forward rotation (forward) slow, but the same applies to reverse search, reverse slow, etc. Based on the above basic principle,
It is obvious that the required displacement waveform can be easily created.

Next, an embodiment of the reproducing circuit section of the present invention will be described. FIG. 5 shows a block diagram of the reproducing circuit. Fifth
The reproducing circuit shown in the figure not only generates the necessary displacement waveforms during variable speed reproducing shown in Figs. This is an example of a reproducing circuit configured to also generate a king control signal.

In Figure 5, 8 is a pulse signal oscillator, and 9 is a sawtooth wave generator composed of a counter and a D-A converter, which corresponds to Figures 2c and d and 3 and 4c and d. Generates the sawtooth waveform required for search and still playback. Immediately after the counter is reset, the sawtooth wave generator 9 counts the number of pulses output from the oscillator 8 and outputs a level corresponding to the number. A reset pulse for the counter is generated by a reset pulse generator 10 from the input head switching signal. This reset pulse is applied to each head 4.
Immediately after the end of the playback period of the head 5 (referred to as CH-1) and the head 5 (referred to as CH-2), it is output from the reset pulse generator 10 as a pulse with an extremely short width. This reset pulse is CH-1
There are two types of pulses, one for CH-2 and one for CH-2. Therefore, there are two sawtooth wave generators 9, one for CH-1 and one for CH-2. Below, as shown in the figure, circuit 1
1, 12, 19, 20, 21, 22, 23, 32
All have two systems, one for CH-1 and one for CH-2,
In order to make the drawings easier to read, these are shown together in one block diagram. The same goes for other parts,
At locations where two types of lines, a solid line and a broken line, are shown, two systems of signals, CH-1 (solid line) and CH-2 (broken line), are output. FIG. 6 shows signal waveforms output from circuits 8, 9, and 10. The output of the sawtooth generating circuit 9 is a sawtooth wave having a period of 2 fields as shown in FIG. By changing the oscillation frequency of the oscillator 8, the P-P value of the sawtooth wave can be changed. The pulse oscillator 8, the sawtooth wave generator 9, and the reset pulse generator 10 together constitute a sawtooth wave generation circuit that generates a sawtooth wave according to the variable tape speed. 11 is a high-pass filter that removes the DC component of the output of 9. 1
2 is a gain adjuster, which adjusts the piezoelectric bimorph displacement sensitivity,
Corresponding to the bimorph drive amplifier gain, etc., gain adjustment is performed so that the piezoelectric bimorph is appropriately displaced. It also has the effect of reversing the polarity depending on the running speed and running direction of the playback tape. 1
Reference numeral 9 denotes an adder, which is used to add signal waveforms (3rd and 4th
(corresponding to e and f in the figure) are added. Reference numeral 20 denotes a low-pass filter, which functions to blunt the waveform of the rapid level change portion of the sawtooth waveform to prevent displacement ringing caused by resonance from occurring in the piezoelectric bimorph. It also has the effect of eliminating jaggedness in the waveform caused by D-A conversion as shown in FIG.
21 is a gain switching circuit that changes the level of the sawtooth wave during a search according to the search speed. Specifically, as shown in FIG. 2, the sawtooth wave level is set to such a level that the piezoelectric bimorph is displaced by 2(n-1)P in total amplitude, and the level is switched based on information that determines the search speed. 22 is an adder in which signals for auto-tracking, which will be described later, are added. 23 is also an adder, and this is because the auto tracking method of this embodiment is different from any wobbling method (the head is forcibly vibrated in the track width direction,
For this purpose, a sine wave signal for head vibration, which will be described later, is added. 32 is an adder to which the DC level from the DC level generator 33 is added. This DC level is used to compensate for the head level difference when assembling the head.
Alternatively, it may be used to generate a head step difference during an odd-numbered speed search as described above, or to generate a necessary step difference during slow playback as shown in FIGS. 3 and 4. Adder 3
The output of 2 is input to the drive amplifier of the piezoelectric bimorph.

Next, a signal generation circuit for additional displacement during slow playback will be described. Reference numeral 13 designates a slow reset pulse generation circuit, and as shown in FIGS. 3 and 4, during 1/2 slow, CH- as shown in FIG.
1 reset pulse is counted down by 1/2,
Also, at 1/4 throw, it counts down to 1/4. In other words, the countdown is performed at the same rate as the slow speed ratio. As for CH-2, as is clear from FIGS. 3 and 4, the reset pulse has a waveform obtained by delaying the CH-1 reset pulse by one field. 14 is a sawtooth wave generator similar to 9, which inputs the output of the oscillator 8 as a pulse signal counted down by the counter 16 by the slow speed ratio, and generates a reset pulse in exactly the same way as 9 with a reset pulse from the reset pulse generator. to generate a sawtooth waveform. The output of the sawtooth wave generator 14 has the waveform shown at e and f in FIGS. 3 and 4.

The slow reset pulse generation circuit 13, the sawtooth wave generator 14, and the counter 16 together constitute a sawtooth wave generation circuit for slow playback that generates an additional sawtooth waveform to be added to the still playback waveform necessary for slow playback. are doing. 15 is a level adjuster, 12
Similarly, the gain is adjusted so that the displacement of the piezoelectric bimorph due to this sawtooth signal becomes a desired value (in this case, 2 track pitches). If necessary, polarity reversal is also performed here. 17 is a switch,
It is turned off except during slow playback, and the signal is not input to the adder 19.

Next, we will discuss signal generation for vibrating the piezoelectric bimorph for wobbling. 24 is a frequency multiplier circuit which multiplies the head switching signal by an odd number.
This can be easily accomplished using a phase lock loop (PLL) circuit. As mentioned above, the odd number multiple of the head switching pulse is
By multiplying by an odd number, CH-1 and CH-2
This is because the direction of head displacement is reversed at the same position on the TV screen, canceling out the effect of a drop in the reproduced FM signal level due to head vibration. Generally, when scanning the center of the recorded track, the playback FM
The signal level change is twice the vibration signal frequency, and even if the change is an odd number, the head displacement direction will not be reversed as described above.
Although FM signal level changes are not canceled out,
In this case, since the level change itself is small, it is not noticeable on the screen. However, when scanning a position offset from the track center, the reproduction FM level change becomes the same frequency as the vibration signal frequency, and the change is large. The level change in this case can be offset by setting the vibration frequency to an odd multiple of the head switching pulse repetition number, that is, the frame frequency. Furthermore, when the same azimuth head is used, head vibration causes jitter on the screen, but when the azimuth angle is the same, the effects of jitter can be canceled out by multiplying the azimuth angle by an odd number and displacing the heads in opposite directions. Therefore, when using the same azimuth head, it is most preferable to use an odd multiple of the head switching pulse.

A band pass filter 25 extracts only the fundamental frequency component from the output of the frequency multiplier 24, outputs a sine wave of the fundamental frequency, and removes harmonics and DC bias. 26 is a level adjuster for adjusting the amount of head vibration. The output of the level adjuster 26 is input to the adder 23, and the same sine wave is added to the signals for both channels.

Next, the tracking error signal generation circuit will be described. The reproduced FM signal is amplitude modulated by the head vibration mentioned above. The reproduced FM signal is subjected to envelope detection by an envelope detection circuit 27 and input to a multiplier 29 . The other input of the multiplier 29 is a signal obtained by adjusting the phase of the output of the low-pass filter 25 by the phase adjuster 28. The phase adjuster 28 is for correcting the phase shift between the head drive sine wave signal and the actual head displacement, and is unnecessary if the sine wave frequency is sufficiently lower than the piezoelectric bimorph resonance frequency. The output of the multiplier 29 is supplied to a low-pass filter 30, where the input fundamental wave and its harmonic components are removed. The output of the low pass filter 30 is a tracking error signal, which is supplied to the analog switch 31. analog switch 3
1 receives the head switching signal as input, and separates the tracking error signal into a signal for the CH-1 reproduction period and a signal for the CH-2 reproduction period. The value of each tracking error signal during the non-reproduction period is interpolated by means such as pre-holding as necessary. Reference numeral 34 denotes a servo loop characteristic compensation circuit, which is composed of a low-pass filter, a phase lead circuit, a phase delay circuit, and the like. A gain adjuster 35 adjusts the loop gain of the entire servo loop. If necessary, the polarity of the servo loop is reversed so that the entire servo loop constitutes a negative feedback system. The output of the gain adjuster 35 is supplied to the adder 22 and added to the signal for variable speed reproduction.

By adding an auto-tracking signal to the sawtooth signal for variable speed playback as described above, fluctuations in tape running speed during variable speed playback, head level differences (due to temperature changes, changes over time, etc.), track bending, etc. can be suppressed. compensation, and it is possible to always obtain variable-speed reproduction images of good image quality without noise bars.

As described in connection with FIG. 2, in the present invention,
As for the amount of head displacement, a dynamic range that is twice or approximately twice the required dynamic range is required during the non-scanning period. If this value becomes too large, a problem will occur. A large dynamic range is required when the search speed is very large. In this case, by shifting the DC level of the waveforms shown in FIGS. 2c and 2d, it is possible to widen the speed range in which good noise barless variable speed reproduction can be performed. The waveform in this case is shown in FIG.

The DC level required for this purpose is supplied by a DC level generator 33 shown in FIG. 7th
As shown in the figure, even if a certain level or more is clipped due to the circuit's dynamic range, etc., in the present invention, the bending point shown by "A" in FIG. There is a very high possibility that the dovetail displacement ringing will be converged within this period, and therefore it is unlikely that it will not adversely affect the reproduced image quality.

In the embodiments described above, variable speed playback heads having the same azimuth angle are used, but the present invention is not limited thereto; for example, heads 4 and 5 may have different azimuth angles, It is clear from the above description that the present invention is also applicable to a configuration in which heads 1 and 2 are not provided, and heads 4 and 5 perform recording and reproduction at normal speeds. Although the wobbling method has been described as a method for obtaining a tracking error signal, the present invention also relates to a so-called pilot method in which a tracking pilot signal is recorded on a recording track and then reproduced to obtain a tracking error signal. It is obvious that this can be applied. Although a piezoelectric bimorph is used as an electromechanical transducer for obtaining head displacement, other types of electromechanical transducers may be used, for example, electromagnetic members such as electromagnets.

〔Effect of the invention〕

As described above, according to the present invention, the electromechanical transducer drive signal for obtaining the head displacement required for various variable speed playback modes is always a simple periodic waveform, even when the drive signal waveform is complex. This can be generated very easily by a combination (addition) of the following, and it is possible to prevent ringing, track deviation, etc. from occurring even when the head starts scanning the tape. Therefore, according to the present invention, it is possible to easily realize a helical scan type video tape recorder that is inexpensive, highly reliable, and can perform playback without noise bars even in the variable speed playback mode.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the head arrangement in the device of the present invention, FIG. 2 is a diagram explaining the principle of the device of the present invention and is a diagram showing the time course of head displacement during forward search, and FIG. FIG. 4 is a diagram showing the time course of the head displacement during forward 1/2 speed slow speed in the embodiment of the device of the present invention. FIG. Fig. 5 is a block diagram of a circuit that generates a signal for driving an electromechanical transducer; Fig. 6 is a diagram showing a signal waveform of a part of the circuit in Fig. 5; Fig. 7 is a diagram showing the passage of time;
The figure shows the time course of head displacement when the search speed is high. 1, 2, 4, 5... Rotating magnetic head, 3... Rotating cylinder, 6, 7... Piezoelectric bimorph, 8...
Pulse oscillator, 20...Low pass filter, 24
...Frequency multiplier circuit, 27...Envelope detection circuit,
29... Multiplier.

Claims (1)

[Scope of Claims] 1. In a variable speed playback device for a video tape recorder having a configuration in which a rotating magnetic head is displaced by an electromechanical transducer for each channel, track pitch is shifted to the rotating magnetic head via the electromechanical transducer. A sawtooth wave generation circuit for still reproduction generates a sawtooth voltage that provides twice or approximately double the displacement amplitude, and a slow wave generator that generates a sawtooth voltage with a period that is an integral multiple of the rotation period of a rotating magnetic head. a sawtooth wave generation circuit for reproduction; an adder for adding the output of the sawtooth wave generation circuit for still reproduction and the output of the sawtooth wave generation circuit for slow reproduction; a drive amplifier for driving a mechanical transducer;
1. A variable speed playback device for a video tape recorder, characterized in that the variable speed playback device for a video tape recorder is configured to be controlled to be at a position opposite to a scanning period based on a scanning start point position. 2. The sawtooth wave generating circuit for slow playback varies linearly or substantially linearly for a period that is an integral multiple of the rotation period of the rotating magnetic head, starting at or near the end of tape scanning of the rotating magnetic head;
Claim 1 further comprises a configuration in which a sawtooth wave voltage is generated for controlling the electromechanical transducer to give the rotating magnetic head a displacement amplitude that is twice or approximately twice the track pitch. Variable speed playback device for the video tape recorder as described.