JPS6326457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic tracking device for a helical scan video tape recorder.

In recent years, in the video tape recorder mentioned above,
In order to ensure that the video head accurately scans the track on which the video signal was recorded during playback,
So-called automatic tracking devices are being developed. For example, Journal of the Television Society (1978)
As described on pages 839 to 841 of Vol. 32 No. 10, as a method of automatic tracking, a video head is attached to the free end (movable part) of an electromechanical transducer such as a piezoelectric element. (The electro-mechanical conversion element moves in a direction perpendicular to the recorded track.) A dither (DITHER) signal is applied to the above conversion element, and changes in the envelope of the reproduced signal are synchronized with the above dither (DITHER) signal. A method has been proposed in which track deviation information is obtained through detection and a negative feedback loop is constructed. In particular, to improve tracking performance,
The frequency of the above DITHER signal is several 100Hz.
It is shown to be set to .

However, when the above method is applied to a video tape recorder that records and plays back with a video head that has an azimuth angle, if the dither signal is set at several 100 Hz as described above, the effect of the azimuth angle will be Jitter (time axis fluctuation) occurs. That is, from the viewpoint of jitter, the frequency of the dither signal must be set to, for example, 120 Hz or less. Along with this, a problem arises in that the followability of tracking deteriorates. In other words, if you set the frequency of the DITHER signal to a low sample rate such as 120Hz,
When it becomes difficult to obtain tape compatibility of the video track angle with an automatic tracking device, or when the electromechanical transducer is configured with a piezoelectric element with a bimorph structure, the nonlinearity of the applied voltage-video head tip position characteristic can be automatically corrected. There is a problem in that it becomes difficult to correct using a tracking device.

Even if the DITHER signal has a low sample rate of about 120Hz, the present invention uses n (for example, 4) low-frequency By supplying the information to the filter, track deviation information in n/2 sections within one scanning period of the video head can be obtained, and the above-mentioned problem can be solved. Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 is a diagram showing the configuration of the main parts of an embodiment of the present invention, and FIGS. 2A to 2L are diagrams showing signal waveforms of each part in FIG. 1. In FIG. 1, 1 and 2 are video heads (rotating magnetic heads), and these are electromechanical transducer elements 2, such as bonded piezoelectric elements with electrodes attached on both sides.
1 and 22 are attached to the free ends of the tips. The other ends of the electro-mechanical transducers 21 and 22 are attached to the rotary disk 4. Reference numeral 3 designates a magnet for detecting the rotational phase of the video heads 1 and 2, which is also attached to the rotary disk 4. A magnetically sensitive rotational phase detector 5 is installed on the fixed part side corresponding to the magnet 3. The rotating disk 4 is driven by a DC motor 37 via a rotating shaft 6, and is rotated at high speed in the direction of an arrow 25. Since a well-known phase control means for the rotary disk 4 can be used, a description thereof will be omitted here. Further, the magnetic tape 23 is driven in the direction of arrow 24 by a capstan 38 and a pinch roller 39.

Output signals of video heads 1 and 2 (hereinafter referred to as
The RF signals (referred to as RF signals) are supplied to stationary preamplifiers 9 and 10 via rotary transformers 7 and 8, respectively. The output signals of the preamplifiers 9 and 10 are sent to the FM demodulator 33 via a video head switching switch 11.
The signal is supplied to the output terminal 34 via the envelope detector 12 and to the synchronous detector 13 as a multiplication means. Said switch 11
is driven by a signal (hereinafter referred to as a head switch signal) obtained by passing the output signal of the rotational phase detector 5 through a pulse delay circuit 35. The synchronous detector 13 is supplied via a phase shifter 15 with an output signal from a dither signal generator 14 that generates a dither signal, which is a drive signal. Note that the output signal of the dither signal generator 14 is triggered by the output signal of the pulse delay circuit 35. The output signal of the synchronous detector 13 is supplied to low pass filters 16, 17, 18 and 19. These low pass filters 16, 17, 18 and 19
The output signal of the pulse generating circuit 20 is also supplied to the pulse generating circuit 20. The low pass filters 16, 17, 18 and 1
The output signals of 9 are added by an adder 36. The output signal of the adder 36 is further added to the output signal of the phase shifter 15 in an adder 40, and then sent to the high voltage amplifier 3.
1 and 32. In the high voltage amplifiers 31 and 32, the electro-mechanical conversion elements 21 and 22
conductive brushes 29, 30 and slip rings 26, 2.
7 to the electro-mechanical conversion elements 21 and 22 as a displacement signal. Note that the slip rings 26 and 27 are attached to the rotating shaft 6.

In such a configuration, the two-channel RF signal reproduced by video heads 1 and 2 is converted to one-channel RF signal by switch 11 as shown in FIG. 2A.
converted into a signal. Note that the RF signal shown in FIG. 2A shows a case where a dither signal (DITHER), which will be described below, is not applied to the electro-mechanical conversion elements 21 and 22. FIG. 2B shows the head switch signal output from the pulse delay circuit 35.
When the head switch signal is at H level, the RF signal of video head 1 is output from switch 11,
At the L level, the RF signal of the video head 2 is output. Further, FIG. 2A shows that the video track angle is different from that at the time of recording, so that the level of the RF signal is sloped. (However, it is assumed that the negative feedback loop described below is broken at the output point of the adder 36.) FIG. There is.

FIG. 2D shows the output signal of the phase shifter 15 applied to the synchronous detector 13. This signal is a signal dither ((DITHER) signal) obtained by phase shifting the output signal of the dither signal generator 14 triggered by the head switch signal by the phase shifter 15, and has a frequency of 120 Hz.
It has a certain phase difference with respect to the head switch signal.

FIG. 2E shows how the envelope of the RF signal changes when the DITHER signal is applied to the electro-mechanical conversion elements 21 and 22. However, the negative feedback loop is
Suppose that the line is cut off at output point 6.

Figure 2 F shows the envelope detector 12 at that time.
is the output signal of The synchronous detector 13 is shown in FIG.
The signal shown in FIG. 2 is multiplied by the signal shown in FIG. 2D, and the multiplication result shown in FIG. 2G is output. This output signal is time-divided in low-pass filters 16, 17, 18 and 19, and then each signal is integrated. As a result, Figure 2 H, I, J and K
A DC voltage as shown in is obtained. Here, an example of the configuration of the low-pass filters 16, 17, 18, and 19 and the pulse generation circuit 20 is shown in FIG. 3, and the input/output relationship of signals of the pulse generation circuit 20 is shown in FIG. In FIG. 3, the pulse generation circuit 20 includes a first delay circuit 101, a second delay circuit 102, a third delay circuit 103, a fourth delay circuit 104, a fifth delay circuit 105, and a sixth delay circuit. 106, a seventh delay circuit 107, and an eighth delay circuit 108, the input signal of these delay circuits (i.e., the output signal of the pulse delay circuit 35) is set to θ ₀ , and each of the output signals is set to θ ₁ , θ ₂ , θ ₃ , θ ₄ , θ ₅ , θ ₆ , θ ₇ and θ ₈ in FIG. Note that these delay circuits include a low-pass filter 16 composed of an ordinary mono-multivibrator, etc.
9, a resistor 110, a capacitor 111, an operational amplifier 112, and a second gate circuit 113. Low-pass filters 17, 18 and 19 also have a similar configuration. In the low-pass filter 16, the first gate circuit 109 supplies the input signal to the resistor 110 only when the above-mentioned signal θ ₁ is at H level. The resistor 110 and the capacitor 111 constitute an integrating circuit with a time constant of T. That is, the input signal is time-divided and further integrated. The integrated result is as shown in FIG. 2H. FIG. 2H represents a certain level of DC voltage. Similarly, low pass filters 17, 18 and 19
The integration results obtained are shown in FIG. 2, I, J, and K. Furthermore, such a DC voltage is applied to the second gate circuit 113, the fourth gate circuit 118, the sixth gate circuit 123, and the eighth gate circuit 12.
8 and added by an adder 36. These gate circuits also supply the above-mentioned DC voltage to the adder 36 when each output signal of the pulse delay circuit 35 is at H level. The output signal of adder 36 is shown in FIG. 2L. The signal shown in FIG. 2L represents the error voltage in the negative feedback loop. That is, the electro-mechanical conversion elements 21 and 22 have a second
By applying the signal shown in FIG. L as a drive signal, one scanning period of the video heads 1 and 2 can be divided into two sections, and track deviation can be effectively corrected. Note that in this example, n=4
As described above, if n=8 is set, one scanning period can be divided into four and each error voltage can be obtained, which allows for more accurate track deviation correction.

Moreover, regarding the running speed of the magnetic tape 23,
It does not necessarily have to be the same as that during recording, and it also holds true in trick plays such as double speed, triple speed, or reverse single speed.

As is clear from the above description, according to the present invention, the video head can be made to accurately scan the recorded video track during playback, and high-quality playback images can be reproduced. The effect is remarkable in realizing a video tape recorder.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the main parts of the embodiment of the present invention, Fig. 2 is a signal waveform diagram of each part thereof, Fig. 3 is a concrete block diagram of the main parts of the embodiment, and Fig. 4 is a signal waveform of each part thereof. It is a diagram. 1, 2... Video head, 3... Magnet for rotational phase detection, 5... Rotational phase detector, 12...
Envelope detector, 13... Synchronous detector, 14
...DITHER signal generator, 16...First low pass filter, 17...Second low pass filter, 18...Third low pass filter, 19...Fourth low pass filter, 2
0...Pulse generation circuit, 36...Adder.

Claims (1)

[Claims] 1. An automatic tracking device for a helical scan video tape recorder, which comprises an electro-mechanical transducer element capable of moving a rotating magnetic head approximately perpendicularly to a video track of a magnetic tape in response to an electrical signal, and the electro-mechanical transducer. a dither signal generator that displaces the position of the video head by a predetermined amount by supplying a dither signal to an element; an envelope detector that detects an envelope of a signal reproduced from the rotating magnetic head; and an output of the envelope detector. a multiplication means for multiplying the signal by the output signal of the signal generator; a plurality of low-pass filters that integrate for each section; an addition means for adding each output signal of the plurality of low-pass filters and the dither signal; and an output signal of the addition means to the electro-mechanical conversion element. An automatic tracking device characterized by comprising a signal applying means for applying a signal.