JPH0542731B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable speed playback device for a helical scan VTR that can obtain good playback images without noise bars.

Conventionally, in broadcasting VTRs, so-called variable speed playback, in which playback is performed at a speed different from that during recording, has been performed without noise bars. However, it is a 1 head system for broadcast VTRs, and 2 heads for home VTRs.
The method is different from the head method, and the variable range of playback speed is narrower. For this reason, even if the technology of broadcasting VTRs is applied to home VTRs, it is not possible to obtain reproduced images without noise bars at the wide range of playback speeds of home VTRs.

Therefore, the conventional two-head helical scan
VTRs had the disadvantage that variable speed reproduction images without noise bars could not be obtained.

The object of the present invention is to perform variable speed reproduction without noise bars in a two-head helical scan system. In particular, it is an object of the present invention to move the head to be reproduced next at an appropriate position and speed at the time of head switching so that there is no image disturbance at the time of head switching.

The feature of the present invention is that the same tracking error signal is always supplied to the two heads to move the two heads at the same speed, and the position shift amount is adjusted according to the playback tape speed and the amount of displacement of the rotating magnetic head. The point is that the required amount of position shift is achieved by one or more position shifts during a period when the magnetic head is not in charge of reproduction.

First, before describing embodiments of the present invention, the principle of the present invention will be explained.

FIG. 1 is for explaining the head arrangement of a rotating cylinder to which the present invention is applied.
FIG. Rotating magnetic heads 1 and 2 (hereinafter simply referred to as heads) are glued onto piezoelectric bimorphs 3 and 4, respectively. The piezoelectric bimorphs 3 and 4 are cantilevered against a rotating cylinder 5 at their other ends remote from the heads 1 and 2. Then, by applying a voltage to the electrodes of the piezoelectric bimorphs 3 and 4, the tips are displaced in the direction of the rotation axis (in the direction perpendicular to the paper plane in FIG. 1),
The heads 1 and 2 can be displaced in the width direction of the recording track. A head position moving device using a piezoelectric bimorph is well known in broadcasting VTRs and the like, and is not the main focus of the present invention, so a detailed explanation will be omitted here.

Note that the explanation here will be directed to an azimuth recording type helical scan VTR. For this reason,
Heads 1 and 2 have different azimuths.
Furthermore, the heads 1 and 2 may be used for both recording and reproduction, or may be heads for reproduction only.

In the following, the principle of the present invention will be explained in detail using an example in which a tracking error signal is detected by a so-called wobbling method, assuming a VTR having the above-described magnetic head.

As is well known, in the wobbling method, sinusoidal vibration is applied to the heads 1 and 2, and due to the phase difference between the envelope waveform of the reproduced output waveform and the vibration waveform,
This is to obtain tracking errors.

Therefore, in the case of variable speed playback, the head automatically traces the recording track based on this tracking error signal. Therefore, if left as is, the head will trace successive tracks in the same way as in normal playback. Therefore, if variable speed playback is to be performed, it is necessary to instruct a track corresponding to the speed of the variable speed at the time of head switching, and to move the head to be played next to that position. This amount of movement is referred to as a position shift amount.

Generally, in the case of variable speed playback of a times speed, the average positional shift amount in one field period is (a-1)p (1) where p is the track pitch amount.

However, if an instantaneous shift is made at the time of head switching, recorded tracks with different azimuths cannot be reproduced, so in the case of the configuration shown in FIG. 1, the allowable position shift amount is 0 or an even multiple of the track pitch.

Therefore, if m is the closest even number (or 0) that is smaller than (a-1), the position shift amount at the time of head switching is m×p and (m+2).
Repeat ×p an appropriate number of times, and on average (a-1)
If it is set to p, variable speed playback of a times the speed can be performed. The above is the principle of the present invention.

The basic idea of the present invention in concretely implementing the above-described principle is the following two points. The first point is the position shift (m
x p) [or (m+2) It is to perform a position shift of the amount [(m+2)×p] (or m×p).

The second point is that in the two-head helical scan system, the above-mentioned position shift is carried out during the period when the head is not in charge of reproduction, and the drive amplifiers of the two heads always have the same torque. By applying a king error signal, both heads always move at the same speed except for position shifts, and the head to be played next is driven at the correct speed regardless of changes in tape speed. By doing this, it is possible to extremely easily pull the servo into the recording track of the rotating magnetic head at the time of head switching, and to prevent the generation of noise bars or screen disturbances at the time of head switching. can.

An embodiment of the present invention will be described below with reference to FIG. FIG. 2 shows, as an example, changes in head position when the tape is reproduced at a speed four times the tape speed at the time of recording, with the vertical axis representing the amount of head displacement and the horizontal axis representing time. Further, p in the figure indicates one track pitch.

In such a case, since a in the above equation (1) is 4, (a-1) in the equation (1) becomes 3. Therefore, in this embodiment, the position shifts of 2 track pitches and 4 track pitches are repeated the same number of times on average. Preferably, this should be repeated alternately.

FIG. 2A shows the required positions and amounts of movement of heads 1, 2. If bimorphs 3 and 4 are to be driven by the same drive amplifier, as shown in Figure A, the 4 track pitch and the track pitch shift must be performed instantaneously, and the direction must be changed instantaneously to pull in the track. , which is impossible. Note that a positional shift in this direction, that is, a shift in the direction of a track recorded later in time, is defined as a shift in the positive direction.

FIGS. 2B and 2D show the displacement of each head when the present embodiment is applied and reproduction is performed at four times the speed. In FIGS. 2B and 2D, the solid line portion shows the displacement during the period when the head is in charge of reproduction, and the broken line portion shows the displacement during the period when the head is not in charge of reproduction. Second
When the solid line parts in Figures B and D are combined, Figure 2A is obtained. This example uses an auto-tracking method, so
In reality, it responds to track bends, etc. Therefore, the movement trajectory of the head is a curved line, but for simplicity, it is set as a straight line.

Head position shifting is accomplished by applying pulses such as those shown in FIGS. 2C and 2E to the integrator input in the servo circuit. As shown in FIGS. 2C and 2E, each of these positional shifts occurs during a period when the head is not in charge of playback.

The first shift occurs immediately after the end of the head regeneration period, and the next shift occurs approximately in the middle of the period when no regeneration is in charge. Figure 2 is an example of 4x speed, so
There are both a 4-track pitch position shift and a 2-track pitch position shift, and the decision as to which one to use is made immediately before the position shift at the center of the period in which playback is not in charge. (The point at which the arrows in Figure 2 B and D are marked) Set the threshold level q drawn with the two-dot chain line in Figure 2 B and D, and at the time when the arrow is marked, the head position will be lower than this level. In the case below, the shift at that point will be 4 track pitches (as of ○A). Then, the position shift performed immediately after the end of the reproduction of the head that was in charge of reproduction at that time is also set to be the same amount (time point ◯).

On the other hand, at the time of level judgment, the threshold level q
If it is higher, a shift of 2 track pitches is made (time point ○), and the subsequent shift (time point ○) is made by the same amount.

Specifically, the position is always shifted by 2 tracks, and at times ○A and ○B, the position shift is further added by 2 tracks. By performing the above position shift, the head position change shown by the broken line is obtained.

As can be seen in FIG. 2, by shifting the track position twice, the amount of head shift can be significantly reduced, thereby lowering the required dynamic range of the entire system. Also, except when shifting, the head in charge of regeneration and the other head move at the same speed.
Pulling into the track at the time of head changeover is extremely easy.

FIG. 3 shows a circuit block diagram for realizing the head position movement shown in FIG. 2.

In FIG. 3, reproduction signals reproduced from magnetic tape 51 by heads 1 and 2 are amplified by amplifiers 6 and 7, respectively. Reference numeral 9 denotes a cylinder rotation tack signal generator, which generates a reproducing head switching pulse SW30. The reproduced signal amplified by the amplifiers 6 and 7 is switched at appropriate timing by a switch circuit 8 controlled by the switching pulse SW30, and becomes a reproduced FM signal.

The reproduced FM signal is envelope-detected by an envelope detection circuit 10, and a synchronous detection circuit (multiplier) 1
1. The other input of the synchronous detection circuit 11 is supplied with a signal obtained by phase-shifting the output of the oscillation source 12 that causes the piezoelectric bimorph to vibrate in a sine wave (wobble) by a phase shift circuit 13 . This phase shift circuit 13 is for making the output of the oscillation source 12 have the same phase as the vibration of the actual piezoelectric bimorph.

The output of the synchronous detection circuit 11 is supplied to a low-pass filter 14 for removing the fundamental wave and high frequency of the wobbling frequency. The output of the filter 14 is subjected to servo system gain adjustment by a gain adjuster 15, and becomes a tracking error signal. The tracking error signal is applied to adders 16 and 17, where a position shift pulse is added to each adder and supplied to integrators 18 and 19, respectively.
The outputs of the integrators 18 and 19 are supplied to adders 20 and 21, where the outputs of the oscillator 12 are added together.
The outputs of adders 20 and 21 are sent to drive amplifiers 22 and 23.
The signals are amplified and drive bimorphs 3 and 4, respectively, which in turn drive heads 1 and 2.

On the other hand, when the switching pulse SW30 is input to the shift pulse generation circuit 24, a shift pulse is generated from the shift pulse generation circuit at a predetermined timing. Shift pulses for heads 1 and 2 are shown in FIG. In FIG. 4, pulse a is a shift pulse for head 1, and pulse b is a shift pulse for head 2. First, the heights of these shift pulses are changed by gain adjusters 25 and 26, respectively, based on the speed signal from the tape speed detection circuit 32. Subsequently, additional pulses are added by adders 27 and 28, and a polarity determining circuit 2 consisting of a polarity inversion circuit, a switch, and a gain adjustment circuit is added.
Supplied on 9,30. As the tape speed detection circuit 32, a frequency generator attached to a capstan shaft or a capstan drive motor shaft or means for measuring time intervals of control pulses can be used.

The direction of the track position shift is different when the tape speed is faster than the recording tape speed and when it is slower or reversed. For this reason, current tape running mode information is obtained from the system control circuit 31 of the VTR, and it is determined whether the polarity of the pulse is to be a positive voltage pulse or a negative voltage pulse. Also, since the track pitch amount p changes depending on the tape speed during recording, the gain is adjusted by the gain adjusters 25 and 26 as described above.

The outputs of the polarity determining circuits 29 and 30 are added to the tracking error signal in adders 16 and 17, respectively, and these are integrated by integrators 18 and 19 to achieve the position shift of heads 1 and 2.

On the other hand, the outputs of the integrators 18 and 19 are
Polarity determining circuits 33 and 34 comprising a polarity inverting circuit and a switch select whether to invert the polarity or not, depending on the tape running mode information at that time. Thereafter, the signal is supplied to level comparison circuits 35 and 36.

In the level comparison circuits 35 and 36, the threshold level supplied from the threshold level generation circuit 37 and the output from the polarity determination circuits 33 and 34 are compared. As explained in connection with FIG. 2, it is determined whether the outputs from the polarity determining circuits 33 and 34 have become lower than the threshold level at the time of level determination in the direction of increasing tracking error due to the difference in recording and reproducing speeds. It will be judged.

When the outputs from the polarity determination circuits 33 and 34 become lower than the threshold level, the levels of the level comparison circuits 35 and 36 become high level. This level change is determined by flip-flops 41 and 42 at the time when clock pulses e and f (see FIG. 4) outputted from shift pulse generation circuit 24 are generated. Incidentally, the clock pulse e occurs near the center of the non-reproducing period of the head 1. If the output of the level comparison circuit 36 is at a high level at the time when the clock pulse e is generated, this high level is held by the flip-flop 42 until the next clock time. Similarly, the flip-flop 41 is clocked by the pulse f shown in FIG.
At the center of the non-reproduction period, it is determined whether the output of the comparator circuit 35 is at a high level. If the level is high, this high level is the flip-flop 41.
is held until the next clock.

The output of flip-flop 42 is connected to gates 43 and 4.
4, and if the flip-flop 42 output is at a high level, pulses e and d pass through the gate. Pulse e passes through adder circuit 48, has its level adjusted by level adjuster 49, and is supplied to adder 27 as an additional pulse. Then, the amount of position shift at the center of the non-reproducing period of head 1 is further increased. On the other hand, the pulse d passes through the adder 47 and the level adjuster 5
The level is adjusted to 0 and the signal is supplied to the adder 28.
As a result, the amount of positional shift of the head 2 at the end of reproduction is further increased.

Similarly, when the output of the flip-flop 41 goes high, the shift amount of head 2 at the center of the non-reproduction period and the shift amount at the end of reproduction of head 1 are increased. As mentioned above, the additional pulse provides an additional position shift of two track pitches to the head. Furthermore, as mentioned above, the outputs of the gain adjusters 25 and 26 change the track pitch amount (a-
1) smaller and equal to giving the head a position shift times the nearest even number.

The above equation (1) also holds true when the tape is running in reverse or when it is played back at slow speed. However, in this case, the outputs of the gain adjusters 25 and 26 are larger than the track pitch amount (a-1), and the position shift is the amount multiplied by the nearest even number (negative even number) (or 0). It's fine if you give it.

For example, in the case of slow playback, 0<a<1, so the even number (or 0) closest to (a-1) and larger than this is 0. Therefore, the position is not normally shifted, but only when the threshold level is exceeded, the position is shifted by two track pitches in the opposite direction to that shown in FIG. In this case, the polarity determining circuits 29, 30, 3
Similar to the case of reverse rotation, the polarities of 3 and 34 need to be reversed compared to the case of normal rotation with a reproduction speed faster than the recording speed.

Next, as an example of this, changes in the head position when the present invention is applied to 1/2 forward rotation slow playback will be explained with reference to FIG. FIG. 5A shows the necessary positional movement amount of heads 1 and 2 as in FIG. 2A, and FIG. 5B,
D shows the positional movement of heads 1 and 2, respectively, when the present invention is applied. The time indicated by the arrows in FIGS. 5B and 5D is the time when it is detected by the clock pulses e and f whether the outputs of the polarity determining circuits 33 and 34 in the flip-flops 41 and 42 have become lower than the threshold level q. . At this point, when the outputs of the polarity determining circuits 33 and 34 are smaller than the threshold level q shown in the figure, a position shift pulse is generated. It should be noted that, in comparison with FIG. 2, the determination of whether level q has been exceeded is reversed in FIG. can.

Figures 5C and 5E show the position shift pulses for heads 1 and 2. In this case, the polarity is reversed from that in FIG. The direction of head movement shown in A, B, and D is also reversed from that in FIG.

It is clear from the above description that slow reverse rotation and fast forward reverse rotation are possible by appropriately converting the polarity of the polarity determining circuits 29, 30, 33, and 34 in FIG.

Further, unlike the case shown in FIG. 1, it is also possible to use both heads 1 and 2 with the same azimuth for reproduction only, or to use one for both recording and reproduction and one for reproduction only. It is clear that in this case, the operation can be carried out in exactly the same way as in the case where the azimuth is different, except that the allowable head position shift amount is an odd value (including positive and negative values).

That is, in the case of forward rotation of a times the speed of a and the playback tape speed faster than the recording tape speed, if n is an odd number smaller than (a-1) and closest to this, the gain adjusters 25 and 26 will always adjust the track pitch to n.
A position shift pulse of a magnitude that provides a double head position shift is generated, and the flip-flops 41 and 42
If the output becomes high level, a position shift of two track pitches may be added.

Also, if slow playback is reverse playback, use the odd number (including negative) that is greater than (a-1) and closest to this.
When n', head shifting is always performed taking into account the sign of n' times the track pitch, and when the outputs of the flip-flops 41 and 42 become high level, an additional position shift is performed in the opposite direction.
It is sufficient to shift the position by the track pitch.

The advantage of using the same azimuth head is that in the case of slow or still playback, the same recorded track can be played back for a fixed period of time. Therefore, a slow or still playback screen with good image quality without screen blur can be obtained.

In the above embodiment, in the case of normal rotation (quick viewing), the track pitch is always shifted by m times (however, m is smaller than a-1 and is the closest even or odd number), and the addition is performed by 2 times in the same direction. Performed a truck pitch shift. On the other hand, in the case of slowing or reversing, n times the track pitch in the opposite direction (however, n is a
A shift of the nearest even or odd number greater than -1 was performed, and an additional shift of two tracks was also performed in the opposite direction.

However, the important point is that the position shift amount should be (a-1)×p on average. Therefore, in the case of normal rotation (quick viewing), a shift of m+2 times the track pitch may be performed, and a shift of 2 track pitches may be added in the opposite direction as an additional shift. In this case, it is necessary to reverse the polarity of the additional pulses compared to the embodiment previously described in connection with FIGS. 2 and 3.

Also, in the case of a throw or reversal, the sign should be taken into consideration.
A shift of m' times (where m' is smaller than a-1 and the nearest even or odd number) may be performed, and the additional shift may be a shift of 2 track pitches in the positive direction. In addition, in the case of reversal,
A circuit for reversing the polarity of the pulses may be added between the level adjuster 48 and the adder 27 and between the level adjuster 50 and the adder 28 in the circuit shown in FIG.

Next, as an example, changes in head position in the case of normal rotation slow playback using the same azimuth head will be shown. In this case, a in the above formula (1) is a value between 0 and 1, -1<a-1<0, and the above m is -1
Leave it behind. That is, a shift of one track pitch is always performed in the reverse direction, and when the head position level falls below the threshold level, a shift of two track pitches is added as an additional shift in the forward direction.
As a result, in this case, a shift of one track pitch is performed in the positive direction.

FIG. 6 shows how the head position moves in this case, similar to FIGS. 2 and 5. In FIG. 6, as in FIGS. 2 and 5, A shows the necessary positional change of the head, B shows the movement of the head 1 according to the present invention, and D shows the movement of the head 2.
C and E indicate shift pulses that provide position shifts for heads 1 and 2, respectively.

In this case, at the time of ○A in Figure 6B, the head 1
Since the position of is below the threshold level q, the pulse of ○B and the pulse of ○C add a shift of 2 track pitches in the positive direction to the normal shift amount of 1 track pitch in the opposite direction, resulting in a total of +1 track pitch in the positive direction. This will give a shift of In this case, the polarity determining circuits 29, 30, 33, 34
The polarity of is selected to be non-inverted.

As is clear from the above description of the embodiment, the present embodiment can change the head position correctly for variable speed playback of any tape speed within the movable range of the piezoelectric bimorph. Therefore, even when the tape speed changes continuously, it is possible to respond to this and obtain stable reproduced images without noise bars. Furthermore, although the present embodiment has been described with reference to a two-head helical scan azimuth recording method, the present invention is not limited to this, and is applicable to recording without azimuth (in this case, the allowable shift is an integral multiple of the track pitch). It is obvious that this method can also be applied to cases where the number of heads is large. Further, although the device for moving the head position substantially in the recording track width direction is a piezoelectric bimorph, it is obvious that it may be a device using other electromechanical transducers, such as an electromagnet.

Furthermore, in the description of the embodiments, a wobbling method was used as a tracking error detection means, but the present invention is not limited to this tracking error detection means. For example, the present invention can be applied to tracking error detection using a pilot method in which a pilot signal is recorded on a recording track and then reproduced to obtain a tracking error signal as a tracking error detection means. is self-evident.

In the embodiments described so far, as shown in FIGS. 2, 5, and 6, the positions of heads 1 and 2 are shifted immediately after the period in which they are in charge of regeneration and in the period in which they are not in charge of regeneration. Although this is done twice in the middle, it is also possible to do this only once, immediately after the end of the period in charge of reproduction. Although the required shift amount increases in this case, it is clear from the above explanation that correct operation can be performed by selecting an appropriate position shift amount.
In addition, in this case, the amount of position shift to be performed immediately after the end of the period in charge of playback can be determined by comparing the head position immediately before the end of the period in charge of playback with the threshold level, as explained above. it is obvious.

As described above, the present invention has the great effect that stable and good reproduced images without noise bars can be obtained in all variable speed reproduction including forward and reverse rotation with a simple circuit. be. Further, according to the present invention, the helical scan VTR has a continuously variable speed playback function that reproduces good image quality without being affected by changes in temperature, humidity, tension, etc.
can be provided.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the head arrangement of an embodiment of the present invention, FIG. 2 is an explanatory diagram of head position movement at 4x speed when the embodiment of the present invention is applied to VTR playback, and FIG. Figure 4 is a block diagram of an embodiment of the present invention, Figure 4 is a time chart of pulses generated by the shift pulse generation circuit 24 in Figure 3, and Figure 5 is a diagram of an embodiment of the present invention applied to VTR playback. FIG. 6 is an explanatory diagram of head position movement during 1/2 slow playback. FIG. 6 is an explanatory diagram of head position movement during 1/2 slow playback when another embodiment of the present invention is applied to VTR playback. 1, 2... Rotating magnetic head, 3, 4... Piezoelectric bimorph, 18, 19... Integrator, 22, 23... Piezoelectric bimorph drive amplifier, 24... Shift pulse generation circuit, 35, 36... Comparison circuit, 32... Tape speed detection circuit.

Claims (1)

[Claims] 1. A plurality of rotating magnetic heads, each of which is movably supported by an electromechanical transducer, and when a magnetic tape is reproduced at a tape speed different from that during recording, the recording of the rotating magnetic head is In a variable speed playback device for a helical scan VTR that detects a positional deviation signal with respect to a track and corrects the positional deviation of a rotating head with respect to a recording track, during a period when the corresponding rotating magnetic head is not reproducing signals, The shift pulse of each magnetic head and the pulse superimposed on the shift pulse (hereinafter referred to as
a shift pulse generating means for outputting a superimposed pulse (referred to as a superimposed pulse); a gain adjustment circuit for adjusting the gain of the shift pulse in accordance with a playback tape speed; addition determining means for determining whether or not to add a pulse; means for generating a sawtooth wave signal based on the positional shift amount determined by the gain adjustment and addition determining means and the positional deviation signal; and a drive amplifier to which a sawtooth wave signal is supplied, and by supplying the drive signal output from the drive amplifier to each of the plurality of electromechanical transducers, the corresponding rotating magnetic head reproduces the signal. 1. A variable speed playback device for a helical scan VTR, characterized in that the position of the magnetic head is shifted during a period when the magnetic head is not being played.