JPS6341470B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking device for a video tape recorder or the like.

In recent years, so-called auto-tracking devices have begun to be introduced for the purpose of accurately scanning recorded tracks during playback in video signal magnetic recording and reproducing devices or video signal magnetic reproducing devices that use magnetic tape, such as video tape recorders. Ta. This auto-tracking device is capable of slow playback, which plays back at a tape running speed different from the tape running speed at the time of recording.
In special mode playback such as still playback, first playback, and reverse playback, it is possible to provide a reproduced image free of noise bands. Such auto-tracking devices usually have a magnetic head for reproducing video signals attached to an electro-mechanical conversion element.
A DITHER signal, which is a drive signal, is applied to the electro-mechanical transducer, the position of the magnetic head with respect to the recording track is determined from the DITHER signal and the reproduction envelope of the magnetic head, and a control loop is established so that the magnetic head is on track. It consists of

In this type of tracking device,
If the recording track width is narrow (e.g. 20 μm),
The displacement width of the rotating magnetic head due to the DITHER signal is limited to several μm at most. In other words, the positional information of the rotating magnetic head obtained from the reproduction envelope has an extremely poor signal-to-noise ratio. In order to configure the above control loop with such a signal, it is necessary to insert a low-pass filter with a large time constant in the middle of the control loop, which limits the response of the control loop.
In other words, in a transient state such as when suddenly switching from fast regeneration to reverse regeneration,
There was a problem in that the control loop did not respond for a certain period of time, and noise bands appeared in the reproduced image.

The present invention utilizes information contained in control signals to generate a rotating magnetic head (hereinafter referred to as a video head).
By constantly knowing the positional relationship between the video head and the video track, the video head can correctly scan the video track during special playback such as slow, still, fast, and reverse playback, and when switching the special playback mode, and can reproduce playback images without the head. This not only solves the problem of the tracking system with slow control loop response, but also makes it possible to obtain the same effect even when there is no control loop.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a diagram showing the main part of a video tape recorder in playback mode using an example of the present invention.
In the figure, 1 and 2 are video heads, which are attached to the free ends of electromechanical transducers 21 and 22, such as bonded piezoelectric elements. The electro-mechanical conversion element 21, 2
The other end of 2 is attached to a rotary disk 4.
Reference numeral 3 denotes a rotational phase detection magnet, which is also attached to the rotating disk 4. magnet 3
A rotational phase detector 5 is installed on the fixed part side corresponding to the above. Rotating disk 4 is driven by DC motor 6 and rotates at high speed in the direction of arrow 25. The output signal of a frequency generator 7 attached to the DC motor 6, the output signal of the rotational phase detector 5, and the output signal of the reference oscillator 10 are supplied to a disk servo circuit 8. The output signal of the disk servo circuit 8 is supplied to the DC motor 6 via a drive circuit 9. Thereby, phase control of the rotary disk 4 during reproduction is performed. The magnetic tape 23 is driven in the direction of an arrow 24 by the capstan 11 and a pinch roller (not shown). The capstan 11 is driven by a DC motor 15 via a pulley 12, a belt 13, and a pulley 14. The capstan control circuit 36 is supplied with the output signal of the frequency generator 16 that detects the rotation speed of the DC motor 15 and the output signal of the reproduction speed instruction section 35, and the output of the capstan control circuit 36 is supplied to the DC motor 15. 1
The signal is supplied to the drive circuit 32 of No. 5.

The output signal of the control head 17 and the output signal of the rotational phase detector 20 are input to the arithmetic circuit 33 constituting the signal processing means. The rotational angle of the capstan 11 is detected by the slitted disc 19 and the rotational phase detector 20, and the rotational phase detector 20 outputs a pulse signal corresponding to the rotational angle. For example, when the tape is played back at the same speed as the tape running speed during recording, the rotational phase detector 20 is
Set to output pulse signals.
Since 10 pulse signals are output in the same way even if the running speed is different, this means that the reproduced control signal interval is effectively divided into 10. Hereinafter, the output pulse signal of the rotational phase detector 20 will be referred to as a sub-control signal.

Note that the rotational phase detector 20 is composed of, for example, a light emitting element and a light receiving element, and includes a circular plate 19 with a slit.
This system detects the light passing through a slit bored in the slit, but a gear-shaped body made of a magnetic material is used instead of the slit disk 19, and a magnetic flux detector is used as the rotational phase detector 20. A similar output signal can be obtained using .

The output signal of the arithmetic circuit 33 is supplied to a high voltage amplifier 34. This signal is amplified to a voltage sufficient to drive the electro-mechanical conversion elements 21 and 22,
The voltage is applied to the electro-mechanical transducers 21, 22 via conductive brushes 29, 30, 31 and slip rings 26, 27, 28. Note that the slip rings 26, 27, and 28 are attached to the rotating shaft 18 of the DC motor 6.

FIG. 2 is a block diagram showing an example of the configuration of the arithmetic circuit 33 shown in FIG. In the figure, a control signal, a sub-control signal, and a head switching signal (hereinafter referred to as head SW pulse) are input to input terminals 51, 52, and 53, respectively.
By performing calculations as described below, information for correctly tracking the video head on the video track can be obtained at the output terminals 54 and 55. Also,
38 in the figure is a main counter constituting a first sub-control signal counting circuit which is reset by a control signal. Reference numerals 39 and 40 denote A and B output counters constituting a second sub-control signal counting circuit which is preset at a certain time by the output of the main counter 38, and these are counters for the reproducing rotating magnetic field. There are as many as there are heads. 42 is a timing circuit for determining the certain time; 41 is a still pattern generator that generates a still pattern signal necessary for correcting the tilt of the video track and video head for correct tracking during still image reproduction; The output signals of the output counters 39 and 40 are added to the still pattern signal by adders 43 and 44, and outputted to output terminals 54 and 55. Note that 46 is each counter input, into which a sub-control signal is input. Further, 47 is a preset input, 45 is a preset data input, 48 is a reset input, 49,
50 is a still pattern signal output.

Next, the operation of this arithmetic circuit 33 will be explained.
For convenience of explanation, the A and B output counters 39 and 40 are removed from the circuit of FIG. 2, and the information of the preset data input 45 is directly input to the adders 43 and 4.
The circuit shown in FIG. 3 will be explained below. Since we are considering application to a two-rotation head type video tape recorder, the two video heads are A and B, the video head scanning when the head SW pulse is at the H level is the A head, and the L is the video head scanning when the head SW pulse is at the H level. The video head scanning at the level is called the B head. Here, the still pattern signal referred to in the present invention will be explained. This signal is a triangular wave signal shown in FIGS. 5A and 5B and described later. The still pattern signal is a pattern signal that corrects the difference between the scanning locus of the video head and the inclination of the video track during still image reproduction, and its amount corresponds to 0 at the beginning of track scanning and 1 pitch at the end.

FIG. 4 shows the scanning trajectory of the video head when the tape is stopped at a position where it is on-track with respect to the video track at the point where the video head begins scanning. In the same figure,
56 is a video track, 57 is a magnetic tape, 58
59 and 60 represent the scanning locus of the video head, and the directions of movement of the magnetic tape and the video head during normal reproduction, respectively. Two-head video tape recorders are designed to always on-track when the magnetic tape is being fed at normal speed, so when the magnetic tape is stopped, the video head will not move at the end of the scan, as shown in Figure 4. 1 pitch off. The still pattern corrects this deviation, and is a signal with a maximum amplitude of 1 pitch, which shows a value proportional to the cylinder rotation angle and is synchronized with the head SW pulse.

FIG. 5 shows the relationship between the still pattern signal and the head SW pulse for the two heads A and B. In the same figure, A is the still pattern signal waveform for the head, B is the still pattern signal waveform for the B head, and C is the still pattern signal waveform for the head.
shows the head SW pulse waveform.

If this waveform is constantly applied to the video head's electro-mechanical transducer, when the tape stops, the head trajectory due to the rotation of the cylinder will be corrected and become parallel to the video track, so that the video head can be adjusted at any given time. The amount of deviation between the tape and the video track is a constant amount that is independent of the rotation angle of the cylinder and depends on the tape position.

Next, the main counter 38 will be explained.

The main counter 38 is a sub-control signal counter that is reset with a control signal recorded once per frame, and its output waveform is shown in FIG. 6A, and the control signal is
Shown in Figure B.

Now, position the control head so that the video track coincides with the corrected head trajectory at the moment the control signal is output. Also,
The video track at that time will be called _Ao track, and the control signal (pulse) will be called _Xo .

First, the physical meaning of the counter output Y _(t) at time t will be explained. This amount is the control signal
Since the number of sub-control signals proportional to the amount of tape movement is counted from the time when X _o is output, the amount is also proportional to the distance between the corrected head trajectory and the video track A _o . In other words, the distance to the next track is 2 pitches, so if we convert the vertical axis "10" in Figure 6A to 2 pitches, we get Y _(t)
indicates the distance of the video head to the A _o track at time t.

FIG. 7 shows the relationship between the magnetic tape 67 and the corrected head trajectory 61 at that time. In the figure, 65 and 66 are control signals X _o , X _o+1 ,
68 is the video track _Ao , 62 is the center of the video track, 63 is the distance between the corrected head trajectory and the video track _Ao , 64 is the control head, and 69 is the video head.

As more time passes and the magnetic tape moves,
Control signal X _o+1 appears and main counter 3
8 is reset, the output of the main counter 38 is
A _o+1 track Indicates the distance to the corrected video track.

Generally, the output Y _(t) of the main counter 38 indicates the distance to the Ao track, where _Xo is _the control signal output immediately before time t.
That is, Y _(t) represents the distance from the corrected head trajectory to the nearest video track in the direction of tape travel.

Also, the nearest track is updated one after another as the tape moves. The output of the main counter 38 is added to the output of the still pattern generator 41 in adders 43 and 44 in FIG. 3, and then output.
By applying these outputs to the electro-mechanical transducers of both the A and B heads, the video head continues to scan correctly on the video track at any tape speed. That track is the track closest to the head in the direction of tape travel, as described above.

Although FIG. 3 is shown to explain the arithmetic circuit 33, if left as it is, the following problems will occur. That is, the video track closest to the corrected head trajectory is updated every time a control signal is output, but when playing back at any tape speed, this update may occur in the middle of the screen. In other words, it appears as a noise band on the screen to move to the next track in the middle of the screen.

Figure 8 shows the output of the main counter and the head at that time.
Shows SW signal.

FIG. 9 shows the playback screen at that time, and shows that a noise band 71 appears in the middle. This width is determined by the response speed of the electromechanical transducer, and if the response is fast, it can be narrowed to an unnoticeable level, but it remains in principle and becomes noticeable especially when the tape feed speed is faster than the normal speed. appears.

In order to compensate for the drawbacks of the configuration shown in FIG. 3, the configuration shown in FIG. 10 can be considered. This eliminates the output counters 39 and 40 in the configuration of FIG. 2, and instead uses A and B.
A common output counter 72 is used. The output counter 72 is a sub control signal counter that is preset using the output of the main counter at the beginning of each field, that is, at both the rising and falling edges of the head SW pulse.

FIG. 11 shows its operating waveforms. In the figure, 70 is the output waveform of the main counter 38, and 73 is the output waveform of the output counter 72. Since the noise band 79 is preset at the falling edge 76 of the head SW pulse waveform and the track is updated, the noise band 79 is hidden in the vertical blanking period.

That is, in the configuration shown in FIG. 3, the video head is
Regardless of the cinder rotational phase, the corrected head trajectory scans the closest track in the tape traveling direction. However, in the configuration shown in Figure 10, the video head is related to the cylinder rotational phase, and the video head starts scanning. At that time, the corrected head locus continues to scan the closest track in the tape traveling direction, and does not move on to the next track until it has finished scanning that track. According to this method, when playing back from stills at several times higher speed,
It is possible to obtain reproduced images that are free from interference due to blinding noise, including transient states of speed changes. Note that the preset timing was set at the starting point of each A and B field. As a result, the update of the scanning track is hidden in the vertical blanking period, but if the response of the electro-mechanical transducer is not fast, sufficient masking cannot be achieved in the vertical blanking period. Furthermore, when an electromechanical transducer such as a piezoelectric element is used, ringing occurs due to the mechanical resonance of the element, even after the vertical blanking period.
A problem arises in that scanning continues with ringing still remaining. This ringing causes mistracking and appears as noise at the top of the screen. To avoid this, it is effective to shift the preset timing to a point a little earlier than the beginning of the field. However, in the configuration shown in Figure 10, if the timing is simply made faster, the track will be updated in the middle of the previous field, so A,
An output counter is used for each B head, and presets are performed separately just before each field. Figure 12 shows the operation of each part at that time, and the tape feed speed is different from normal running.
This is a diagram when the speed is 1.5 times, that is, 1.5 times the speed. Further, the phase with respect to the head SW pulse for tape feeding is not particularly specified. In the figure, A is the main counter output waveform, B is the control signal, and C is the head
SW pulse, E and G are preset pulses for each head of A and B, D and F are counters 3 for each output of A and B
This is the output waveform of No.9,40. After this, adder 4
Since the 3 and 44 still pattern signals are added, waveforms shown by solid lines in FIGS. 13B and 13D appear at the output terminals 54 and 55 of the arithmetic circuit 33. The still pattern signal waveforms at that time are shown in A and C in the same figure, respectively, and the output counter waveforms before adding the still pattern signal are shown by broken lines in B and D in the same figure. Further, an arrow 80 indicates a period during which head A is tracking, and an arrow 81 indicates a period during which head B is tracking. 1st
As shown in FIGS. 2E and G, preset timing is performed independently at the front 1/3 field of each field and at the end of each field. Therefore, the sudden change in waveform occurs at least 1/3 field before the beginning of each field, so
This can prevent delays in the response of the electromechanical transducer due to these changes and mistracking due to ringing.

Next, it will be explained that the present invention can also be applied to reverse playback.

The above explanation applies to high-speed playback from stills, but exactly the same results can be obtained in high-speed playback from stills in reverse. However, when reversing, it is necessary to input the sub-control signal to each counter in a down-count manner. That is, the second
By using up-down counters that can handle negative numbers as the main counter, A output counter, and B output counter shown in the figure, you can switch between up and down depending on the tape feed direction, from high-speed reverse playback to high-speed forward playback. Good tracking is achieved in all modes regardless of the capstan servo.

Note that since the forward/reverse switching signal of the counter needs to accurately follow the actual tape feeding direction, it is better to create it using a sub-control signal.

FIG. 14 is a diagram showing an example of a circuit that generates forward and reverse signals using two types of sub-control signals FG ₁ and FG ₂ that differ in phase by 90°. In other words, the sub control signal with a phase shift of 90° is transferred to the D flip-flop.
By inputting to the input terminal and T input terminal, Q
The forward and reverse signals are obtained from the output terminal. FIG. 15 shows a timing chart during forward/reverse reversal in FIG. 14. In the figure, a broken line 82 indicates the actual tape feeding order reversal timing, and 83 indicates the above-mentioned timing.
FG1, 84 and FG1, 85 indicate forward and reverse signals.

FIG. 16 shows the relationship between the vertical peak value of the output waveform of the arithmetic circuit 33 of FIG. 3 and the reproduction speed. In the figure, 86 indicates the maximum waveform value, and 87 indicates the minimum waveform value. This head drive signal waveform is
As the tape feeding speed increases, it tends to expand upward, that is, in the tape running direction, and when the tape is reversed, it tends to expand downward. By the way, if this voltage is applied to the electro-mechanical conversion element, the necessary head swing width will be too large, exceeding the dynamic range of the electro-mechanical conversion element, or the head output will decrease due to deterioration of the head touch. . Therefore,
In such a case, it is necessary to perform a correction process by adding an occupied area correction means based on speed as described below to the output of the arithmetic circuit 33 shown in FIG. That is, the correction is performed by detecting the tape feed speed and, when the waveform begins to expand upward, by subtracting a voltage equivalent to two pitches at a certain speed from the waveform. When the rotation is reversed, addition is performed in the opposite manner. The switching speed is set so that the waveform is always near the center of the dynamic range of the electro-mechanical conversion element, and the value is, for example, -2, 0,
When 1.5 times the speed is selected, the speed-dependent correction voltage applied to the output of the arithmetic circuit 33 in FIG. 2 becomes as shown in FIG. 17. As a result of this correction, as shown in Figure 18, the head drive signal waveform increases almost vertically as the speed increases, resulting in exceeding the dynamic range of the electro-mechanical transducer and deterioration of the head touch. It is possible to alleviate the decrease in head output due to

FIG. 19 shows an example of the configuration of one channel of the occupied area correction circuit that can be used in the present invention. In the figure, 88 is an input terminal connected to the output terminal of the arithmetic circuit 33 in FIG. 2, and 89 is an output terminal. Further, 90 is an adder, 91 is a speed-to-voltage conversion circuit that measures speed using a sub-control signal, etc., and 92 is a voltage comparator.
It switches at three points, 0 and 1.5 times the speed, and generates a voltage of 2n pitch (where n is 2, 1, 0, -1). 93
is a timing circuit that does not apply the voltage generated here as it is, but delays it until the time when the head is not reproducing to avoid moving to the next track in the middle of the reproducing field. It can be constructed from a flip-flop or the like.

In the above embodiment, a configuration was explained in which the output counter (second control signal counting circuit) is preset within the previous field, but it is also possible to preset the output counter (second control signal counting circuit) at the end time of the previous field, that is, the start time of the current field. Similar effects can be obtained.

As is clear from the above description, according to the present invention, even if the tape feed speed during playback is set to an arbitrary feed speed between several times the standard feed speed and several times the reverse speed, or even if the tape feed speed during playback is Since the rotating video head always correctly tracks the video track even in a transient state, a very excellent effect can be obtained in that a completely noise-free reproduced image can always be obtained. In order to reproduce the control signal at any running speed, it is preferable to use a magnetic flux response type head composed of a Hall element or a magnetoresistive element as the control head 17.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main part of a video tape recorder implementing an example of the present invention, FIGS. 2 and 3 are diagrams showing an example of the configuration of an arithmetic circuit that can be used in the present invention, and FIG. 4 is a still image playback diagram. Fig. 5 is a waveform diagram of the still pattern signal and head SW signal, Fig. 6 is an explanatory diagram of the operation of the main counter,
Fig. 7 is a diagram showing the relationship between the head trajectory and the video track when tape running is stopped, Fig. 8 is a signal waveform diagram of each part of Fig. 3, Fig. 9 is a diagram showing an example of the playback screen, and Fig. 10 is a diagram showing the relationship between the head trajectory and the video track when tape running is stopped. Diagrams showing other examples of arithmetic circuits,
Fig. 11 is an operation waveform diagram of Fig. 10, Figs. 12 and 13 are signal waveform diagrams of each part of Fig. 2, and Fig. 14
The figure shows an example of a forward/reverse signal generation circuit, FIG. 15 is an operating waveform diagram of the circuit in FIG. 14, and FIG.
Figure 17 is a characteristic diagram of the occupied area correction circuit according to speed, Figure 18 is the occupied area diagram after correction, and Figure 19 is an example of the configuration of one channel of the occupied area correction circuit. FIG. 1, 2...Video head, 3...Magnet, 5...
Rotational phase detector, 8... Disk servo circuit, 11
...Capstan, 17...Control head, 1
9... Disc with slit, 20... Rotational phase detector, 2
1, 22...Electro-mechanical conversion element, 23...Magnetic tape, 33...Arithmetic circuit, 38...Main counter, 39...
A output counter, 40...B output counter, 4
1... Still pattern generator, 42... Timing circuit, 43, 44... Adder, 72... Output counter.

Claims (1)

[Scope of Claims] 1. A video signal is recorded as an inclined video track on a magnetic recording medium by a rotating magnetic head, and control signals are recorded on the recording medium at regular intervals in the longitudinal direction of the recording medium. It has a sub-control generating device that generates a sub-control signal which is proportional to the amount of travel of the recording medium and effectively divides the control signal when reproducing the recording medium at a traveling speed different from that during recording. A tracking device for a video signal recording and reproducing apparatus in which a head is changed in a direction substantially perpendicular to a video track using an electro-mechanical conversion element, the first sub-control signal counting being reset by a control signal during reproduction. a second sub-control signal counting circuit that is preset using the output of the first sub-control signal counting circuit in the previous field for a signal synchronized with the rotation of the rotating magnetic head; a triangular wave generator for correcting the difference in slope between the track and the head scanning locus, and an arithmetic circuit for outputting a signal obtained by adding the output of the second sub-control signal counting circuit and the output of the triangular wave generator, A tracking device characterized in that an output voltage of an arithmetic circuit is applied to the electro-mechanical conversion element to move a rotating magnetic head in a direction substantially perpendicular to a video track. 2. In the description of claim 1, the second sub-control signal counting circuit and the triangular wave generator are each provided in plural numbers, and are adapted to drive and control a plurality of rotating magnetic heads. tracking device.