JPS581843A - Automatic tracking device of vtr - Google Patents

Abstract

PURPOSE:To keep the optimum tracking state even in a variable speed reproduction mode, by providing a means that varies the tracking shift degree of a servo circuit in both forward and backward directions with each unit degree and detecting and deciding the increasing/decreasing direction of the reproduced signal level obtained before and after the change of the tracking shift degree. CONSTITUTION:The control signal (b) sent from a control track 4 is reproduced by a control head 12 and fed to a control microcomputer 15. The signal (b) is delayed by a unit degree and applied to a capstan servo circuit 14 to give a shift to the tracking. Then the tracking is shifted by a unit degree, and the reproduced signal level (f) obtained after the tracking change is compared with the reproduced signal level obtained before the tracking change through a comparator 11. When an increase is detected for the reproduced signal levels before and after the tracking change, the changing direction of the tracking is kept as it is. While the changing direction of the tracking is reversed when the reproduced signal level has a decrement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a rotating 2-helical helical scan type VT.
Regarding auto-tracking devices such as R.

In a rotating two-heave type helical scan type VTR, a synchronization control signal is recorded at the end of the magnetic tape during recording, and during playback, this control signal controls the (b) dislocation of the capstan or rotation/rad cylinder. It performs phase control and operates so that the video signal recording track of the magnetic tape is traced correctly. therefore,
As long as the track of the video signal on the recorded magnetic tape and the phase of the control signal are maintained correctly, tracking will always be performed accurately.However, if the VTR used for recording and the VTR used for playback are different,
Alternatively, if the length of the recorded magnetic tape changes due to aging or other factors, the relative phase relationship between the recording track and track of the video signal on the magnetic tape and the control signal may differ from the VTR standard during playback. This does not match the tracking state, causing a deviation in tracking, resulting in deterioration of the S/N of the reproduced video signal and disturbance of synchronization in image reproduction. This problem of tracking deviation is becoming increasingly important as tracks become narrower with longer recording times.

This is recorded for 2 hours using the VH5 method, and in the case of a 6-hour recording method with a recording speed of 1A (track pitch 193 μm).
To explain this using a diagram, for example, as shown in FIG. 1, when a recording track 2 of a video signal is recorded on a magnetic tape 1 and a corresponding control signal is recorded on a control track 4, the control signal and the recording track 2 has changed, or when the distance between the control head and rotation cylinder of the VTR during playback is different from that of the VTR during recording, The tracking by the control signal is deviated, and the actual tracking by the rotary cylinder becomes, for example, as shown by a shaded rectangle 5 T. In addition, when recording and reproducing data for 2 hours and 6 hours using a head with the same head width (19.5 to 50 μm is appropriate, here we use 193 μm), a 39 μm guard band will occur during 2 hours of recording, which is due to tracking deviation. In addition, compatibility with mutually recorded tapes becomes a further problem, and in extreme cases, it may not be played at all.

Therefore, in the past, a tracking adjustment knob was installed on the VTR, and the servo control circuit of the capstan or cylinder was manually adjusted to set the phase difference between the control signal and the head switching signal obtained by rotation/rad cylinder rotation to a standard value. I changed it from 1 to 3 and adjusted it to get the best tracking while looking at the screen. Therefore, not only the operation is complicated and inconvenient to use, but also there are many inconveniences such as erroneous operation may cause the device to become unusable and be determined to be malfunctioning.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to be able to automatically correct tracking not only in standard playback but also in variable speed playback, and to improve the performance as the length of playback increases. The purpose of the present invention is to provide VTR auto-tracking that can compensate for narrow track compatibility.

In order to achieve this object, the present invention provides a means for constantly changing the tracking shift lid of the servo circuit by a standard amount in both forward and reverse directions, and detects and judges the direction of increase or decrease in the playback signal level before and after the change each time there is a change. The feature is that the optimum tracking state is always maintained by changing the direction of change in tracking as it is when increasing, and switching the direction of change in the opposite direction when decreasing.

Embodiments of the present invention will be described below with reference to the drawings.

Figure wJ2 is a block diagram of an auto-tracking device for a VTR according to an embodiment of the present invention. In this figure, 5
6 is a rotating cylinder, 6 is a cylinder motor, and 7 is a head start signal d that detects the rotation phase of the rotating cylinder 5 and indicates the point in time when the rotating head 8 starts scanning the magnetic tape 1.
9 is a preamplifier that amplifies the reproduced Eirin FM signal (usually recorded as FM in VTR), which is the output of the rotary head 8. AGC is used to control the output sent to the normal signal system at a constant level. is hung, 10
1 corresponds to the level of the envelope of the reproduced signal by sampling pulse 1, and a sample hold circuit holds the AGC control voltage, which is a signal with an expanded envelope level change. 11 is the AGC control control voltage small output! A comparator that outputs an increase/decrease signal by comparing the
12 is a control head that reproduces control signals from the control track 4; 15 is a capstan motor for running the tape; 14 is a capstan servo circuit that controls tracking; and 15 is a microcomputer for control. # Example behavior! Waveform diagram of each part in Figure 3 and yi
This will be explained using a flowchart shown in GA.

When the auto-tracking operation starts at the start of playback, etc., the initial tracking value is first set. In this embodiment, the delay of the control signal is used to change the tracking, so this corresponds to the tracking amount. 1! ! Set the initial value of the extension tt to °to.

If this initial tracking t0 is set so that optimal tracking can be achieved with a standard tape, the response speed of auto-tracking can be increased.

If the relative position of the recording track 20 and the control signal is incorrect in this state, mistracking as shown at the left end of the diagram A of the body 6 occurs, and the head 8 can pick up signals only in the shaded area.

Next, the playback signal level f before changing the tracking
(Fig. 5 (!I)), sampling pulse z (llI
5 (c)) is outputted from the microcomputer 15 to the sampling and hold circuit 10 for sampling, and a hold output 1 is obtained. this#! It is shown by the dotted line in Figure 3 (b). Next, the tracking is shifted by changing the delay amount t of the control signal in the positive direction by a unit amount of 4t and applying it to the capstan servo circuit. This amount of tracking change is shown in wIs diagram 0 as a staircase waveform. After shifting the tracking by a unit amount, operate time delay 1 until the servo circuit stabilizes, and change the playback signal level f after the change to $
It is detected at the time of the detection pulse number shown in FIG. In the figure, since the reproduced signal level is in the increasing direction, the increase/decrease discrimination signal becomes "H1" as shown in Figure 5 (C). Therefore, the direction of change in tracking is good up to that violet, so it is shown in the flowchart of Figure 4. Return the sampling to the output routine as shown below, increase the delay cover after 4 seconds while maintaining the level before the change by a unit of 1iit (Wg delay amount becomes to + 2Jt), and detect the increase/decrease direction of the playback signal level f before and after the change. Make a judgment and continue the above actions at all times.

If the increase/decrease discrimination signal becomes "L'," which means that the playback signal level has decreased before and after the change, it means that the tracking shift has gone too far, so we move to a routine that decreases the tracking by "it" in the opposite direction. Then, the direction of increase/decrease is determined in the same way, and if it is increasing, the delay amount is increased immediately.If it is decreasing, the delay amount is increased.By continuing the above operation,
An auto-tracking operation is performed to always keep the reproduced signal level f at its maximum.

In the above explanation, the reproduction signal level f is detected by one of the heads 8.
The scanning period, that is, the random phase of the reproduced video signal is used for detection, but by reading the fFld of the head 8 in FIG. As shown in FIG. 5, the recording track 20 and the reproducing head trajectory 21 generally do not coincide. The reproduction signal level f at this time is the 6th (
2) As shown in Fig. 2, the playback signal level f changes suddenly, but if the playback signal level f is detected before and after the tiger and king changes at the same phase in one field as shown in Fig. It is possible to cancel out and improve the sudden fluctuation range of the automatic tracking device due to level fluctuation.

Next, it is possible to realize an auto-tracking operation with the same configuration that automatically tracks the generated noise band into the planking period not only for standard playback but also when performing variable-speed decubitus at a traveling speed different from that during recording. shows. FIG. 7(b) is a waveform diagram of the reproduced output signal f of the double-speed automatic transmission.

The detection phase of the level f before and after the change should be set near the head start signal d (showing one of the two heads), that is, near the vertical blanking period, as shown in Figures 7 (G) to ρ. Since the auto-tracking operation works so that the level is maximum at the start of one field, it is possible to drive the noise band to the start of the other field. Similarly, the case of 1A double speed slow motion reproduction is shown in FIG. 8, G4) to G0.

By setting the detection phase so that the maximum value of the playback level f is in the center of a predetermined field, it is possible to add a noise node that appears once every five fields. Since the shape of the envelope of the control signal and the playback signal level f are in a certain relationship,
It can be determined by the microcomputer 15.

In the case of other variable speed magnifications, auto-tracking at variable speed can be similarly realized by detecting and comparing the phase that satisfies the condition that the noise band is driven into the vertical blanking period.

Note that in the above explanation, AGC is used to obtain the reproduced signal level f.
Although the control voltage is used, this may be obtained from a separately provided head output envelope detection means.

Also, the tracking is changed by delaying the control signal added to the servo circuit, but it may also be done by delaying the reference clock α, or by changing various quantities of the cylinder servo circuit instead of the capstan servo circuit. Of course, it is okay to make changes.

Furthermore, although the unit amount explained in this embodiment was constant, this amount becomes the residual deviation of auto-tracking, so it is desirable that it be as small as possible. However, if it is chosen too small, the response time will be long. This contradictory problem can be solved by changing the unit amount appropriately. That is, after auto tracking operation.

When the playback signal level first changes from an increase to a decrease, or from a decrease to an increase, the unit cover can be reset to a smaller value. Also, the auto tracking operation is not constant, but
It is conceivable to do this intermittently as necessary, or to go directly after the playback start operation, and then to fix it.

Although this embodiment has shown an example in which a microcomputer is used for control, it goes without saying that similar functions can be realized using individual circuits.

As explained above, according to the present invention, no matter what kind of recorded tape is played back, tracking is always performed automatically and correctly not only in standard playback but also in variable speed playback, and failures due to operational errors are avoided as in the past. By assembling a microcomputer and configuring it in conjunction with other control functions, it is possible to have a relatively simple configuration, and it does not require complicated operations. You can get tracking.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a recording pattern on a magnetic tape and the tracking state of the head with respect to the pattern, FIG. 2 is a block diagram of an auto-tracking device for a VTR according to an embodiment of the present invention, and FIGS. 4 is a waveform diagram of various parts according to changes in head and track positions for detailed explanation of the present invention, FIG. 4 is a flowchart for explaining the operation, and FIG.
The figure is a plan view showing the head playback trajectory during one field.
! 6 to 8 are waveform diagrams for explaining auto-tracking operations during standard speed, double speed, and 115 times speed playback, respectively. 7...Tack head 8...Head 9...Preamplifier 1o...Sample hold circuit 11.
... Comparator 12 ... Control head 1
4...Capstan servo circuit 15...Micro combiator 1m 12 mouths 3 bacteria (F13i1or hand!l!J(iif, ``”' -
-Fig.
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−−−−The first round

Claims (1)

[Claims] 1. means for changing the tracking of the servo circuit of the VTR by an arbitrary unit amount in both forward and reverse directions; means for detecting and holding the playback signal level before and after the change; There is a means for comparing the repeat signal level, and when the reproduction signal level increases before and after the change, the direction of change in tracking is
4. An auto-tracking device for a VTR, characterized in that it has control means for changing the direction of tracking change in the opposite direction when the playback signal level decreases. 2. The auto-tracking device for a VTR as set forth in claim 1, wherein the playback signal level before and after the change is detected and compared at always the same phase of the playback video signal. 3. When variable speed playback is performed at a running speed different from that during recording, detection and comparison is performed at a phase that satisfies the condition that the noise band is driven into the vertical blanking period according to the variable speed magnification. The automatic tracker and soaking device for a VTR according to item 1 or 2. 4. An auto-tracking device for a VTR according to any one of claims 1 to 5, wherein the reproduction signal level is obtained from an AGC control voltage applied to a head signal amplification preamplifier. 5. A VTR according to any one of claims 1 to 4, characterized in that the tracking is changed by delaying a control signal applied to a servo circuit.
auto-tracking device. & Patent 1iPF characterized in that the initial tracking when the amount of change in tracking of the servo circuit is set to zero is set so that optimal tracking can be obtained with a standard tape. V described in
TR's O1-) Racking device. Z Patent freezing range Paragraphs 1'gi to 6, characterized in that the unit amount is set to a small value when the reproduced signal level first decreases from an increase or increases from a decrease after the auto-tracking operation. VTR described in any of
auto-tracking device.