JPH0123863B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a tracking error correction circuit for ensuring that a rotary head correctly traces a recorded track when playing back a tape in a VTR, and in particular, it relates to a tracking error correction circuit for ensuring that a rotating head correctly traces a recording track when playing back a tape. This invention relates to a tracking error correction circuit that prevents malfunctions even when magnetic powder is not attached due to dust or the like.

[Background technology]

In VTRs, especially home VTRs, high-density recording is performed to reduce tape consumption. For home use, two-head helical VTRs are generally used, and because they perform guard bandless recording, conventional methods have been used to ensure that the two rotating heads correctly trace the video track recorded on the tape. Various improvements have been made. As a representative example, ATF
(Automatic Track Finding) method is available. This system uses a tracking error detection signal to automatically control the tape running system using a servo mechanism, thereby correctly controlling the tape position and the phase relationship between the head cylinders.

A DTF (Dynamic Track Following) method has also been developed to perform noiseless special speed playback. This is a system in which a self-correcting video head is arranged as a special playback head. The special playback head is fixed to an actuator made of a piezoceramic plate with one end fixed to a rotating cylinder.By applying an appropriate control voltage to this actuator based on a tracking error detection signal, recording tracks can be recorded. The head is moved to trace the top accurately (for details, see, for example, TV Technology, December 1981 issue, p. 73).

In both the ATF method and DTF method mentioned above, it is necessary to obtain a tracking error detection signal, and one of them is a tracking error detection circuit of the 4-signal method (for example, see TV Technology, December 1979 issue, p. 89). There is.

In this four-signal system, if the auxiliary signals, that is, the pilot signals fp, each having a constant frequency are designated as f ₁ to f ₄ , they are determined to have a frequency difference of f _T1 and f _T2 , respectively, as shown in Figure 1. It is being These pilot signals fp are transmitted for each track as f ₁ , f ₂ , f ₃ , f ₄ ,
f ₁ , f ₂ , f ₃ , ... are sequentially switched and recorded superimposed on the signal, and during playback, for example, while a track on which f ₁ is recorded, f ₂ or f ₄ are switched on both sides. Since the track on which . is recorded is arranged, f ₂ and f ₄ are picked up as crosstalk, and f ₁ , f ₂ , and f ₄ are output as a reproduced pilot signal f _PB . When f ₁ is mixed with this reproduced pilot signal f _PB , |f ₂ ±f ₁ |, |f ₄ ±f ₁ |, |f ₁ ±f ₁ | appear in the output, and from Fig. 1, f ₂ − Since f ₁ = f _T1 and f ₄ −f ₁ = f _T2 , the direction and amount of deviation are detected based on the magnitude of these amplitudes. In this example, an increase in f _T2 means that the tracking has deviated as shown in d in Figure 2, and an increase in f _T1 means that the tracking has deviated as shown in b. Therefore, if the capstan motor or the like is controlled so that the amplitudes of f _T1 and f _T2 are equal, the state c in FIG. 2 will be maintained and tracking will be achieved.
However, the direction of the head deviation with respect to f _T1 and f _T2 is
Every track is the opposite.

When reproducing the next track on which f ₄ is recorded, signals with a frequency difference f _T1 and f _T2 are obtained in the same manner. In this way, tracking is performed sequentially.

FIG. 3 is a diagram showing the main part of a four-signal type tracking error detection circuit in a conventional two-head helical scanning type VTR. An oscillator (oscillator) that switches the frequency for each track and generates a pilot signal, which is picked up from the video head 1 and frequency-modulated by a low-pass filter (LPF) 2, and is extracted separately from the luminance signal Y and the low-frequency converted color signal C. The two beat components (frequency difference f _T1 , f _T2 ) generated by mixing any of the outputs f ₁ to f ₄ of the ATF OSC) 3 with the mixer (MIX) 4
are taken out through bandpass filters (BPF) 5 and 6, and signals corresponding to the amplitude are taken out through detection circuits (DET) 7 and 8, respectively, and input into a differential amplifier 9. The output of the differential amplifier 9 is an inverting amplifier 10
The control signal (error signal) is output by being alternately switched for each track with the inverted output via the inverter.
Note that the output frequency of the oscillator (ATF OSC) 3 is f ₁ to _{f 4}
The switching is performed by a head switching signal S _H for switching between two heads, and the output of a signal generator (SG) 11 that divides the frequency of the signal by two to generate a switching signal. Further, switching between the output of the differential amplifier 9 and the output of the inverting amplifier 10 is performed by a head switching signal S _H.

By the way, in the conventional circuit as described above, the fourth
As shown in the figure, when heads exist on three adjacent tracks on the tape, the tracking servo means operates in response to a control signal (error signal). Automatic tracking is performed so that the head moves in the direction (←) and in the right direction (→) if it is in the state e.
Now, when the head reaches the O position, it naturally has to move to the left (←).
As shown in the figure, if there is a dropout on the tape near this position, the pilot signal f ₄ will not be detected, and therefore f ₄ − f ₁ = f _T2 should be large, but instead f ₂ − It is determined that f ₁ = f _T1 is larger, and as a result, the servo means operates in the opposite direction (→) to the tracking correction direction (←), and the tracking becomes more and more distorted, and finally the target track is not achieved. It may happen that you miss the mark.

That is, in the conventional tracking error detection circuit shown in FIG. 3, when a dropout occurs, the tracking servo means operates in the opposite direction to the direction in which the head position should be corrected, and it takes time to return to the normal state. This has become a big problem.

[Disclosure of the invention]

The purpose of the present invention is to solve the above-mentioned conventional problems, and to control the tracking servo means (servo capstan and DTF circuit for the tape running system) by turning on and off switches when a dropout occurs on the tape. An object of the present invention is to provide a tracking error correction circuit that minimizes tracking errors.

In order to achieve the above object, the tracking error correction circuit of the present invention inputs input to a video switch provided before the tracking servo means from the dropout detection circuit, and controls the rotation of the capstan or the movement of the head of the DTF method using the switch. on,
By turning it off, auto tracking is temporarily stopped when dropout is detected.

Therefore, according to the present invention, it is possible to prevent the tracking error correction circuit from malfunctioning when dropout occurs.

[Best mode for carrying out the invention]

Next, the present invention will be explained in detail by way of examples.

FIG. 5 is a block diagram of a tracking error correction circuit according to the present invention. The reproduced signal from the video head 1 passes through an amplifier 12 and a dropout detection circuit 13, and is sent to a video signal processing circuit (not shown) and a tracking error detection circuit 14. As the tracking error detection circuit 14, for example, the conventional one shown in FIG. 3 can be used as is. The output of this error detection circuit, that is, the control signal (error signal) output, is transmitted to the tracking servo means (capstan motor or
In this example, a switch circuit (video switch) 16 is provided between the servo circuit 15 and the tracking servo means 17. When the dropout detection circuit 13 detects a dropout and generates a detection signal, the video switch 16 receives the signal and performs an opening/closing operation. That is, when a dropout is detected during playback, the video switch 16 turns off the servo signal from the servo circuit 15 during the period when the dropout occurs, thereby causing a malfunction in the tracking error correction by the tracking servo means 17. I try not to.

As described above, according to the present invention, malfunctions can be prevented by simply adding a simple switch circuit to the conventional tracking error detection circuit, and stable auto-tracking can be performed.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the 4-signal system, Fig. 2 is an explanatory diagram of the tracking operation of the 4-signal system, Fig. 3 is a configuration diagram of a conventional tracking error detection circuit of the 4-signal system, and Fig. 4 is a diagram of the conventional tracking operation. The explanatory diagram, FIG. 5, is a block circuit diagram showing the main structure of the tracking error correction circuit according to the present invention. 1...Video head, 12...Amplifier, 13...
...Dropout detection circuit, 14...Tracking error detection circuit, 15...Servo circuit, 16...
Switch circuit (video switch), 17...Tracking servo means.

Claims (1)

[Claims] 1. When reproducing a tape on which a plurality of pilot signals of different frequencies are repeatedly recorded in a predetermined order on each track, a difference between the pilot signals on adjacent tracks is detected. In a tracking error correction circuit for a VTR, the tracking servo means is operated in accordance with the detection signal, the drop-out detection circuit detects drop-out of the tape, and the tracking servo means is operated according to the output signal of the drop-out detection circuit. A tracking error correction circuit characterized by comprising a switch circuit for temporarily stopping an auto-tracking operation.