JPS6363967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method in which a reproducing rotating head is mounted on a head driving element such as a piezoelectric element in order to automatically perform tracking based on information of a reproducing high frequency signal (hereinafter abbreviated as RF signal). RF
This invention relates to an automatic tracking correction device that prevents the above-mentioned automatic tracking malfunction from occurring when no signal is output, recovers the RF signal output in a short period of time, and smoothly transitions to normal tracking operation. be.

Conventionally, information from RF signals is used to detect the tracking status of the reproducing rotary head and recording track, and the reproducing rotary head is displaced in the direction along the rotational axis of the cylinder (usually in the vertical direction) to achieve good tracking. Various methods have been reported as so-called automatic tracking devices. For example, there is a device that detects an RF signal, sequentially samples the detected output, sequentially compares the sampled outputs, and as a result, displaces the reproducing rotary head in a direction in which the detected output increases. But something like this
It goes without saying that a device that performs a tracking operation based on an RF signal is based on the premise that an RF signal is output.

However, in the next state, no RF signal is output, which means that automatic tracking operation is not guaranteed at all.

One example is a VTR that has a recording head with a narrow track width that slows down the tape speed for long-duration recording, but when recording at normal tape speed with that VTR,
There are sections between recorded tracks where no signal is reproduced. FIG. 1 shows the relationship between recording tracks on a magnetic tape and a reproducing rotary head.

FIG. 1a shows recording heads a 1 and b 1, each having a width of 60 μm and having azimuth angles _A and B, respectively, and a cylinder ₁ .
The recording tracks A ₁ , B ₁ , A ₂ , B ₂ recorded azimuthally when there is a tape movement of 120 μ in rotation are shown. This is the case for so-called standard records.
Figure 1b shows the width with azimuth angles A and B, respectively.
With recording heads a ₂ and b ₂ of 30μ, 40μ per cylinder rotation
It shows recording tracks A ₃ , B ₃ , A ₄ , B ₄ , A ₅ , B ₅ recorded azimuthally when there is tape movement of . This is the case with so-called long-term recording.

Figure 1c shows recording heads a ₃ and b ₄ of width 30μ with azimuth angles A and B, respectively, and one rotation of the cylinder.
The recording tracks A ₆ , B ₆ , A ₇ , B ₇ recorded azimuthally when there is a tape movement of 120 μ are shown.
This is a VTR that can record for long periods of time, and is in a normal recording state.

At this time, the 2
If the movable rotary heads have the same azimuth angle A, for example
If it is, only the tracks recorded at azimuth angle A will be reproduced, and the tracks recorded at azimuth angle B will not be reproduced. Therefore, even if the amount of deviation between the reproducing head and the recording track is the same, the reproduction output will also differ if the recording state differs as described above. Figure 2 shows that in each of Figure 1 a, b, and c,
The RF signal output levels reproduced when the reproduction head is moved 120 μ in the track width direction are shown in a', b', and c'. Looking at this, we can see that in the states a' and b' in Figure 2, the RF signal is almost always regenerated and the automatic tracking operation can be performed without malfunction, but in the state c'
There is a section where no RF signal is reproduced, and when the reproducing head is located in this section, the automatic tracking operation is not guaranteed at all and malfunctions occur. For this reason, a state in which the reproducing head cannot escape from this section, a so-called "drop", occurs. At this time, noise appears all over the television screen, and there is no guarantee when the screen will return to normal, resulting in an extremely unsightly situation.

This is to realize long-term recording of VTR.
This shows that because the head width was narrowed, the conventional tracking operation alone no longer worked.

Second, if there is an unrecorded portion on the tape, no RF signal is output. At this time, if the automatic tracking operation is left as it is, its operation is not guaranteed at all, and high voltage may continue to be applied to the head drive element, causing adverse effects. Furthermore, as shown in Fig. 3, when the next recorded part on the tape comes, there is a possibility that the track will be tracked on a different track than the one that should be tracked, and both heads _a4 and _a5 will be tracking different tracks. If tracking is performed, the television screen will appear blurred, or so-called ``jump'', resulting in an extremely unsightly image. This is caused by the continuous automatic tracking operation, which is meaningless in unrecorded areas.

The present invention solves the above conventional problems, and detects the RF signal level, and when the RF signal falls below a predetermined output, that is, an output at which automatic tracking cannot be performed satisfactorily, the normal automatic tracking operation is performed. , the playback head is forcibly driven, this operation is continued until the RF signal level exceeds a predetermined output, and when the RF signal level exceeds the predetermined output, the normal automatic tracking operation is performed again. The main idea is to quickly bring the head out of the "dropped" state and to prevent "jumping" from occurring when changing from the non-recording state to the recording state.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4 shows a main part block diagram of an embodiment of the present invention. In the same figure, from VTR1
The RF signal is input to the automatic tracking circuit 2 as tracking information and processed. Also,
The RF signal is input to the RF signal level detection circuit 3, the RF signal level is detected, and the result is output to the control circuit 4. The control circuit 4 controls the automatic tracking circuit 2 to stop its normal operation and forcibly perform a predetermined operation based on the signal from the RF signal level detection circuit 3. The automatic tracking circuit 2 is connected to the head drive element 5 of the VTR 1, normally performs automatic tracking operation, and performs RF
The section detected by the signal level detection circuit 3 is
The operation is controlled by the control circuit 4.

Although many circuits are conceivable as the RF signal level detection circuit 3, one example is shown within the broken line frame in FIG. This detects the RF signal with a diode 6, passes it through a low-pass filter consisting of a capacitor 8 and a resistor 7 to ignore dropouts such as tape scratches, and impulse noise, and sets a predetermined threshold with a volume control 9. The signal is output through the transistor 10. The control circuit 4 is determined in accordance with the configuration of the automatic tracking circuit, and there are various possibilities, such as quickly escaping from a "falling" state.
It is necessary to be able to smoothly transition to normal automatic tracking operation. Next, a typical automatic tracking method and the operation of the control circuit for the method will be specifically described.

FIG. 5 shows a block diagram of the automatic tracking circuit and its corresponding correction circuit for one head. This automatic tracking circuit detects the RF signal from the VTR 1 in a detection circuit 11, samples and holds the output in sample and hold circuits 12 and 13 alternately based on a sample pulse generation circuit 17, and sequentially in a comparison circuit 14. As a result of the comparison, the arithmetic circuit 15 determines to achieve better tracking, and the arithmetic circuit 15 controls the head drive element 5 by controlling the applied voltage generating circuit 16 at the next stage. In such a circuit system, the control circuit 4 controls the arithmetic circuit 15. Here, the operation of the control circuit 4 when the RF signal level is below a predetermined level will be described based on FIG. Here, FIG. 6 shows a recording track A having the same azimuth as the reproducing head, the reproducing head locus, the RF output level at that time, and the output from the RF signal detection circuit 3. When a decrease in the RF signal output is detected by the RF signal output detection circuit 3, the reproducing head is gradually displaced by approximately one track pitch (see FIG. 6a). With this action,
When the RF signal does not recover to the predetermined value, it is preset to the displacement start point and then reversed from there to approximately 1
The track pitch is displaced (see Figure 6b).
In other words, the track pitch has been displaced by +/-1, and the nearest recording track is always scanned within this range, allowing a transition to normal automatic tracking operation in a short period of time.

In addition, by continuing the above operation in the unrecorded part, as shown in Fig. 7, when the next recorded part comes, both heads will track to the nearest track, so that the same operation as shown in Fig. 3 will be performed. There is no "jumping" and the automatic tracking operation smoothly transitions. Here, the solid line is for head _a6 ,
The dashed line shows the head locus of head _a7 .

The displacement of ±1 track pitch may be performed several times within one field, or may be performed once in several fields. Furthermore, various forced drive methods can be considered depending on the automatic tracking circuit.

As is clear from the above description, the present invention provides a VTR equipped with a movable reproducing rotary head for automatic tracking based on reproduced RF signals.
When the playback RF signal falls below a predetermined level, the automatic tracking operation is stopped and the playback head is forcibly driven to prevent a "drop" condition and to prevent recorded and unrecorded parts from coexisting. There is no skipping when playing back a tape, and
This prevents abnormal voltage from being applied to the head drive element, and its value is extremely high when it is used in VTRs that can record for long periods of time and have an automatic tracking function.

[Brief explanation of drawings]

Figures 1a, b, and c are diagrams showing examples of recording patterns on tape, Figure 2 is a diagram showing the RF signal output reproduced when the reproduction head is displaced, and Figure 3 is a diagram showing head skipping. 4 is a block diagram of a main part of an embodiment of the present invention, FIG. 5 is a block diagram showing a specific example of the present invention, and FIG. 6 a,
7b is a diagram showing an example of the operation of the control circuit in the embodiment of the present invention, and FIG. 7 is a diagram showing an example of the operation in the unrecorded portion in the present invention. 1...VTR, 2...Automatic tracking circuit,
3...RF signal level detection circuit, 4...control circuit,
5... Head drive element, 11... Detection circuit, 1
2, 13...Sample hold circuit, 14...Comparison circuit, 15...Arithmetic circuit, 16...Applied voltage generation circuit, 17...Sample pulse generation circuit.

Claims (1)

[Scope of Claims] 1. In a video tape recorder equipped with a movable playback rotary head in order to automatically perform tracking based on information of a playback high-frequency signal, at the moment the playback high-frequency signal output falls below a predetermined output. The automatic tracking system stops the automatic tracking operation, and at the same time, the movable reproducing rotary head is moved within a range of one track pitch in each width direction of the recording track around the point where the movable reproducing rotary head has been scanning from the above moment. An automatic tracking correction device characterized in that the automatic tracking operation is performed again when the reproduced high-frequency signal becomes larger than the predetermined output. 2. In the description of claim 1, the automatic tracking system includes an automatic tracking circuit, an RF signal level detection circuit for detecting a reproduced high frequency signal level, and a signal from the RF signal level detection circuit to detect the automatic tracking system. An automatic tracking correction device comprising a control circuit for controlling a tracking circuit.