JPS59223970A - Tracking controlling device of video tape recorder - Google Patents

Abstract

PURPOSE:To reduce considerably the variation of a time until a tracking servo is stabilized by resetting a signal generating circuit by the output signal of a band-pass filter and forcedly making the frequency of the output signal of the signal generating circuit to coincide with the frequency of a pilot signal. CONSTITUTION:When the 4th pilot signal is given to a selecting circuit 14, an output signal having a frequency of f1 out of output signals of a signal generating circuit 13 is given to a mixer 6. Such a condition is regarded as resetting of the signal generating circuit 13. In this way, the frequency of the output signal of the signal generating circuit 13 which is selected by the selecting circuit 14 and given to the mixer 6 becomes f1. On the other hand, a pilot signal which is given to the mixer 6 through a low-pass filter 5 becomes the 1st pilot signal and, eventually, the frequencies of the pilot signal and output signal given to the mixer 6 become coincident with each other. Therefore, the tracking servo when a video tape 1 is set to the reproducing condition from the stopping condition is stabilized, because the frequencies of the pilot signal and output signal become coincident with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a tracking control device for a helical scan type video tape recorder using an azimuth recording method.

<Prior Art> A tracking control device for such a video tape recorder is shown in FIG.

In FIG. 1, reference numeral IVi videotape, 2 and 3 are rotary heads, 4 (l-j: head output amplifier, 5 is a low-pass filter, 6 is a mixer, and 7 is a first unit with a band frequency of 1H (horizontal scanning frequency) Bandpass filter, 8fd A second bandpass filter with a band frequency of 3fH, 9 is a switching circuit that switches and outputs the output of both bandpass filters 7.8, io and 1i alternately receive the output of the switching circuit 9. 1st and 2nd rectifier circuits for rectification, 12 both rectifier circuits 1o and ii
It is a DC amplifier that amplifies the output of

13bfl (-6,5fH), f2 (=
7.5 f mouth), fa (= 10.5 ftl)
14 is a selection circuit that selectively supplies the output signal of the signal generation circuit 13 to the mixer 6.Head output amplifier 4, selection circuit 14 and switching circuit 9 are arranged to perform predetermined operations for each field in response to head switching and ζ pulses.
As shown in FIG. 2, a video track of 15 degrees 15 is formed by the two rotary heads 2 and 31 having an azimuth angle in an oblique direction.
,...The signal is not recorded on the top. This video track 15,15. . . . Above, the first to fourth pilot signals S1°S2 having frequencies as shown in FIG.
S3. S4 is recorded while cycling through each video track individually. Each pilot signal S+, S
2, Ss, S4, respectively, 6.5"H17,5
fH.

It has frequencies of 10.5fH and 9.5fH, and the fourth
As shown in the figure, an FM modulated luminance signal S5 and a low frequency conversion carrier color signal S6 are both recorded on the videotape.

S7 is an FM carrier frequency shift part.

During playback, the tracking control device of FIG. 1 operates as shown in FIG.
．． When tracking a video track in which the first pilot signal S1 is recorded, the first pilot signal of this video track and the numbers of the video tracks on both sides adjacent to this video track are recorded. 4
．． The output obtained by reproducing the second pilot signals S4 and S2 is applied to a mixer 6G via a low pulse filter 5.

Further, the mixer 6 is connected to the signal generation circuit 1 via the selection circuit 14.
3 output signals are provided. Therefore, from mixer 6, the first. 4th. Second pilot signal S+, S4. S
The beat signal of 1.2 and the output signal is the 1st. It is applied to a second bandpass filter 7.8. Both bandpass filters7.
8 outputs a beat signal having a frequency of fH1311I. The levels of both beat signals change depending on the tracking state of the rotary heads 2 and 3 during reproduction.

Therefore, if the level change of this beat signal is obtained as the output of the DC amplifier 12 and this output is used, the tracking state can be controlled.

However, in such a tracking control device,
When the video tape 1 changes from a stopped state to a running state for playback, the pilot signal reproduced by the rotary head 2.3 and the output signal of the signal generation circuit 13 given from the selection circuit 14 to the mixer 6, respectively. If the frequencies of the two bandpass filters 7.8 are different, the level of each beat signal output from both bandpass filters 7.8 becomes large. Therefore, the output level of the DC amplifier 12 increases, and the output level of the DC amplifier 12 increases.
A circuit device (not shown) that receives the output of No. 2 and performs tracking servo operates in response to this change in output level as a tracking error signal. That is, a response operation is performed in the direction of matching the image frequencies of the pilot signal and the output signal. Therefore, in such a tracking control device, the time it takes for the tracking servo to stabilize from when the videotape is stopped to when it is running during playback varies depending on the level and size of each beat signal, so the tracking servo The problem is that the stability of the system becomes very poor.

<Purpose> The purpose of the present invention is to reduce the fluctuation in time until the tracking servo stabilizes when the videotape changes from a stopped state to a running state during playback, and to speed up the stabilization of the tracking servo. .

<Example> Hereinafter, the present invention will be explained in detail based on the example shown in FIGS. 6 and 7.

FIG. 6 is a circuit diagram of this embodiment, and parts corresponding to those in FIG. 1 are given the same reference numerals. The tracking control device according to this embodiment is applied to an azimuth recording helical scan type video tape recorder. This video tape recorder is the first. It has second rotating heads 2 and 3. Both rotary heads 2 and 3 are attached to both ends of a head bar within a tea caddy-shaped cylinder (not shown). Both rotary heads 2 and 3 are arranged in a slit formed around this cylinder so as to face slightly outward from the slit, and the video tape 1 is wound around this cylinder in an Ω-shape. In FIG. 6, the barrel rotary heads 2 and 3 are shown to be in contact with the video tape 1 at the same time, but in reality they are alternately in contact with the barrel rotary heads 2 and 3. The head output amplifier 4 amplifies the outputs of the cylindrical rotating heads 2 and 3 and provides the amplified output to the low-pass filter 5. Of the output signals of the head output amplifier 4, the low-pass filter 5 passes only the first to fourth pilot signals 51 to S4, which have been completely recorded on the video tape 1, and supplies them to the mixer 6. The signal generation circuit 13 outputs a signal having a frequency corresponding to the frequency of the pilot signal. The selection circuit 14 selects the output signal of the signal generation circuit 13 in response to the head switching pulse and supplies it to the mixer 6. The mixer 6 outputs a signal obtained by frequency mixing the first to fourth pilot signals 51 to S4 and the output signal of the signal generating circuit 13. This signal is a beat signal having a frequency difference between the pilot signal and the output signal. Of these beat signals, the first beat signal with a frequency of fH is given to the switching circuit 9 via the first band pulse filter 7, and the second beat signal with a frequency of 3fH is given to the switching circuit 9.
The signal is applied to a switching circuit 9 via a bandpass filter 8. The switching circuit 9 outputs the first beat signal to the first rectifying circuit 10 and the second beat signal to the second rectifying circuit 11 in response to the head switching pulse. First and second rectifier circuits 1
0.11 is the first. The second beat signal is rectified and a rectified output is provided to the DC amplifier 12.

The DC amplifier 12 provides a rectified output (from which a control voltage is applied to, for example, a phase control circuit of a tracking servo (not shown)).

16, the first signal included in the output signal of the head output amplifier 4
- A specific frequency of the fourth pilot signal S+-84,
For example, it is a third bandpass filter that passes only the fourth pilot signal S4 having a frequency of 9.5 fH. 17 is a waveform shaping circuit that shapes the output waveform of the third bandpass filter 16. The fourth pilot signal S4 whose waveform has been shaped by the waveform shaping circuit 17 is applied to the selection circuit 14.

The signal generation circuit 13 is reset via the selection circuit 14 by this fourth pilot signal S4. This reset method will be explained. The selection circuit 14 includes four individual contacts (not shown) and one movable contact, and each of the four individual contacts receives an output signal of each frequency from the signal generation circuit 13. One movable contact sequentially contacts four individual contacts in response to the head switching pulse and is connected to the mixer 6. Therefore, each time the head switching pulse is input to the selection circuit 14, the The movable contact moves the corresponding individual contact and gives the output signal from the signal generation circuit 13 to the mixer 6. However, this selection circuit 14
is passed through the waveform shaping circuit 17 to the third bandpass filter 1
When the fourth pilot signal S4 is given from
The movable contact is forcibly switched to an individual contact corresponding to an output signal having a frequency fl. Therefore, when the fourth pilot signal is applied to the selection circuit 141, the output signal of frequency 11 among the output signals of the signal generation circuit 13 is applied to the mixer 6.

Such a state is said to be caused by the signal generation circuit 13 being reset. In this way, the frequency of the output signal of the signal generation circuit 13 which is selected by the selection circuit 141 and given to the mixer 6 becomes fl. Also, the pilot signal given to the mixer 6 via the low-pass filter 5 is the first pilot signal. Since the signal S1 is obtained, the frequencies of the pilot signal given to the mixer 6 and the output signal eventually match.

Therefore, the tracking servo when the videotape 1 changes from the stopped state to the playback state is stabilized because the frequencies of the pilot signal and the output signal match.

The stability of this tracking servo will be further explained with reference to FIG. FIG. 7(a) shows the waveform of the head switching pulse, and each high level and low level period corresponds to one field. FIG. 7(b) Each output signal of the signal generation circuit 13 given to the U mixer 6 is
, E2. fa and f4. Figure 7 (C
) is a frequency F+, in order to make it easier to understand the correspondence between each pilot signal given to the mixer 6 and the output signal.
f2. These are indicated by fa and f4. Figure 7 (
d) shows the level of the control voltage applied from the DC amplifier 12 to the phase control circuit of the tracking servo. The first period 1'1 is the period when the third bandpass filter 16 and waveform shaping circuit 17 shown in FIG. 6 are not provided, and the second period T2 is according to the embodiment. That is, in the first period TI, the frequency of the pilot signal [Fig. 7(C)
] and the frequency of the output signal [Fig. 7 (1)] do not match, and the degree of mismatch varies, so when the videotape changes from a stop state to a playback state, it is necessary to apply a signal to the tracking servo's phase control circuit. Since the thick σ of the control voltage [FIG. 7(d)] is not constant, the time it takes for the tracking servo to stabilize becomes variable, resulting in a lack of stability in the tracking servo. On the other hand, in the second period T2, the image frequencies of the pilot signal and the output signal always match, so the control voltage fluctuation σ is small and constant, and the time until the tracking servo stabilizes is constant. However, in the end, the transition to the regeneration state can be achieved smoothly.
As described above, according to the present invention, a pantone filter is provided which filters a pilot signal having a specific frequency through a band pass when a videotape changes from a stop state to a playback state.
The signal generation circuit is reset based on the output signal number of the bandpass filter, and the frequency of the output signal of the signal generation circuit is forced to match the frequency of the pilot signal. It is possible to greatly reduce fluctuations in the tracking servo, and the tracking servo can be stabilized more quickly.

[Brief explanation of the drawing]

1 to 5 are used to explain the conventional example, and FIG. 1 is a circuit diagram of the conventional example, and FIG. 2 is a diagram schematically showing the positional relationship between the video track of the video tape and the rotary head. ,
Figure 3 is a frequency distribution diagram of the pilot signal, Figure 4 is FM
The pilot signal combined with the modulated luminance signal etc. and the F
FIG. 5 is a diagram showing a rotating head tracing a video track of a videotape, FIG. 6 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a time chart for explaining the operation of the circuit shown in the figure. 1... Video tape, 2, 3... Rotating head, 4.
... Hera) Power amplification 15, b...Low pass filter, 6...Mixer, 7, B...1st. Second
Bandpass filter, 9... Switching circuit, 12... DC amplifier, 13... Signal generation circuit, 14... Selection circuit, 16... Third bandpass filter, 17... Waveform shaping circuit . Applicant Nyap Co., Ltd. Agent Patent Attorney Kazuhide Okada

Claims (1)

[Claims] ([) A plurality of pilot signals for tracking state detection having specific frequencies in sequence are individually and periodically recorded on the video track of the videotape, and during playback (this pilot signal corresponds to this pilot signal) In a tracking control device for an azimuth recording type helical scan type video tape recorder equipped with a mixer that outputs a beat signal by mixing the output signal of a circuit that sequentially generates signals, the video tape changes from a stopped state to a playback state. A bandpass filter is provided that allows a pilot signal having a specific frequency to pass through the band, the signal generation circuit is reset by the output signal of the bandpass filter, and the frequency of the output signal of the signal generation circuit is set to the frequency of the pilot signal. A tracking control device for a video tape recorder that forces matching σ.