JPS605412A - Tracking control system - Google Patents

Abstract

PURPOSE:To always ensure the stable tracking by sampling a level difference signal between two types of difference frequency signals produced from the reproduced pilot signal obtained in a reproduction mode with the prescribed timing and using the sampled level differene signal as a tracking control signal. CONSTITUTION:The recording/reproducing heads 3 and 4 trace odd and even tracks alternately, and a period while the head 3 is tracing the center part of a track is set as the sample holding timing. Then the tracking control is carried out with use of the level difference signal which is sampled and held at a preceding track in a period during which the other head 4 traces a track. Thus the tracking control signal is always produced only from the level difference signal obtained by the head 3 as long as the sampling/holding timing is set in such a way as mentioned above. Therefore it is not necessary at all to give concideration to the fluctuation of the tracking signal due to the individual difference between heads 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tracking control method for a reproducing head in a recording/reproducing apparatus such as a VTR.

[Technical background of the invention and ranking points]

One of the conventionally known control systems for VTRs and the like is the system described in Japanese Unexamined Patent Publication No. 116120/1983. In this method, when recording an information signal, a multi-frequency pilot signal whose frequency changes cyclically for each tone is multiplexed. (Reproduction pilot containing B) and a reference signal having the same frequency as the pilot signal recorded on the reproduction track are mixed to obtain two types of difference frequency signals, and reproduction is performed from the level difference of these difference frequency signals. This method detects head misalignment.

However, in such a tracking control method, the reproduction A' plot signal obtained from the sliding start part and the sliding end part where the sliding state of the reproducing head on the recording medium is unstable is unstable. There was a problem in that the tracking control signal obtained in some parts became unstable.

In addition, for example, when two playback heads are used by switching alternately, the individual difference C1 (variation % of playback characteristics) between the playback head and the playback head will affect the playback characteristics obtained for each playback head and the drive head. There is a problem in that the tracking control signal is more likely to become unstable because a level difference occurs in the signal or switching noise generated when switching heads is mixed into the reproduction signal.

[Purpose of the invention]

The present invention has been made in view of the above problems, and an object thereof is to provide a tracking control method that eliminates the unstable factors of the tracking control signal and allows stable tracking at all times.

[Summary of the invention]

The present invention is a tracking control method using a multi-frequency pilot signal, in which a sample-hold signal is sampled at a predetermined timing and held at a predetermined timing. The present invention is characterized in that a circuit is provided, and the output signal of the syf hold circuit is used as a tracking and king control signal.

〔Effect of the invention〕

According to the present invention, 2
Various effects can be obtained by not using the level difference signal of different types of difference frequency signals directly as a tracking control signal, but by sampling this at a predetermined timing and using a held signal.

That is, for example, if the level difference signal is sampled and held when the playback head is located in the middle of each track, the level difference signal obtained when the sliding condition between the playback head and the recording medium is at its best is used for playback. If the tracking control signal is used until the head moves to the middle of the next track, the influence of unstable playback pyro and g signals obtained at the beginning and end of sliding of the playback head on the recording medium can be eliminated. Can be canceled.

In addition, when using multiple playback heads by switching between them, the level difference signal of the difference frequency signal obtained by one of the playback heads is sampled and held, and this held signal is used to play the other playback heads. If the tracking and king control signals of the heads are used, stable tracking control can be performed without any problem caused by variations in the reproduction characteristics of individual heads. Moreover, in this case, the output during the head switching period is...
The king control signal is a constant signal that is held and is not affected by noise that occurs when switching heads. Even when a plurality of heads are switched and used in this way, it is possible to eliminate the unstable factors of the tracking and king control signals, and extremely stable tracking control becomes possible.

[Embodiments of the invention]

An embodiment of the present invention will be described below, taking tracking control in a two-head VTR as an example.

In this example, the frequency is fs * f2 mfs ef4
The 4s class pilot signal is used. The relationship between the frequencies fl and fa of each signal and the pilot signal is as shown below.

fx <f2<f4<fs Ifx −ft I=1f* −fs l (=F1
) Ift fa 1=1f* fs 1 (=F2) These four types of pilot No. 44 are placed on each track 2 of the recording medium 1 as fl+fx −fs − as shown in FIG.
Multiple recording is performed in the order of fa.

On the other hand, the VTR is provided with two recording/reproducing heads 3.4 as shown in FIG.
, 4, the head to be reproduced for each track is changed over by the switching operation of the head changeover switch 5.

Now, assume that the recording/reproducing switch 6 is set to the reproduction mode and the recording/reproducing head 3 is selected by a command from the control circuit 7. When this recording/reproducing head 3 traces the track 2a shown in FIG. This includes the p-stoke component 1s-fs from the adjacent track. In the case of a VTR, the frequency band of the noi-pilot signal is generally lower than the low frequency conversion color subcarrier, so the above crosstalk component element 1-fm
is reproduced relatively well. This reproduced signal is guided to a low gas filter 10, and only the reproduced pilot signal is extracted. Furthermore, this reproduced/mother pilot signal is supplied to one input end of the mixer 11.

A reference signal from the oscillator 12 is applied to the other input end of the mixer JJ. The frequency fB of this reference signal
are recorded on the track traced by the recording/reproducing head 3.4 (fl −fx , f
It changes in the order of s - f4. therefore,
In this case, the frequency of the reference signal f! l becomes f2,
The output of the mixer 11 is a difference frequency signal Fs= between the crosstalk molecule 1 lf3 from both adjacent tracks and the reference signal f2.
Fz will be included. These signals are sent to amplifier 13
After being amplified by the dividing circuit 14, it is divided at a predetermined amplitude ratio, and the difference frequency signal 1 is
Only 7-t-Ft is extracted. Further, these two difference frequency signals F, , F2 are respectively applied to both input terminals of the differential amplifier 220 via detection circuits 20 and 21, and the level difference between them is detected. The output of this differential amplifier 22 is
Since the polarity is inverted for each track, the polarity is switched by the polarity switching circuit 23 so that the polarity is constant for tracking deviations in the same direction, and the level difference signal and null are switched. This level difference signal is applied to the sample hold circuit 24, sampled at a predetermined timing by the control circuit 7, and held to become a tracking control signal.

Sample and hold of the level difference signal is performed at the following times. That is, in this embodiment, during recording/reproduction, dos 3 and 4 alternately trace odd-numbered tracks and even-numbered tracks, but the period during which one recording/reproduction head 3 traces the center portion of the track is held as a sandal hold. Set as the timing. During the period when the other recording/reproducing blade P4 traces the track, tracking control is performed using the level difference signal sampled and held in the previous track.

If the sandal hold timing is set like this, the tiger and king control signals will always be sent to one of the recording/playback heads 3.
It is generated using only the level difference signal obtained by. For this reason, there is no need to take into account fluctuations in tracking control signal due to individual differences between the recording/reproducing head 3 and the recording/reproducing head 4. Moreover, the influence of noise accompanying the switching operation of the head changeover switch 5 does not appear on the tracking control signal. As a result, stable tracking control is always possible. In addition, in this case, since the level difference signal is sampled and held every other track, the track and king control signals are always used for tracks and discrepancies in which the output of the differential amplifier 22 is in the same direction. Create a level difference signal with a constant polarity/
It will be shilled and held. Therefore, the extremely large effect that the polarity switching circuit 23 becomes unnecessary is brought about.

Note that the Zangle hold timing of the level difference signal is not limited to the above-mentioned time points. For example, if it is desired to cancel only head switching noise, the sample and hold timing may be set just before the switching period of each head. For example, if the present invention is applied to a method in which one track is divided into two areas and a video signal is recorded in one area and a PCM audio signal is recorded in the other area, once in each area. It is also possible to sample and hold the data.

Furthermore, in the case of a playback device that uses a single head, the effects of the present invention can be achieved by sampling and holding at the point when the recording medium and playback head are sliding most stably. is possible.

Furthermore, in the above embodiment, the method of recording four types of pilot signals with different frequencies in a cyclic manner for tracking was explained as an example, but the number of pilot signals, permutation, etc.
It is not limited to this example. Furthermore, it goes without saying that the present invention can be applied not only to one or two but also to a plurality of Cs.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing a pilot signal recording pattern of a recording medium to explain the principle of the Tiger/King control method using multi-frequency pilot signals, and Fig. 2 shows an embodiment of the present invention. It is a four-dimensional diagram. 1... Recording medium, 3.4... Recording/reproducing head, 24
... Sample hold circuit. Application agent Patent attorney Takehiko Suzue

Claims (3)

[Claims] (1) Record signals whose frequencies cyclically change from track to track on each track on a recording medium together with information signals, and generate two types of difference frequency signals from the reproduced signals during playback. Furthermore, the level difference between these two types of difference frequency signals is detected to generate a tracking control signal having a polarity and level corresponding to the tracking deviation, and this tracking control signal is used to cause the playback head to follow the track. In the tracking control method, a sample and hold circuit is provided that samples and holds a level difference signal between the two types of difference frequency signals at a predetermined timing,
A tracking control method characterized in that the output signal of this Sanzor hold circuit is used as the tracking control signal. (2) For reproduction, the do is composed of a plurality of heads that are selectively switched for each track, and the sample hold circuit is configured to receive a reproduction two-arm pilot signal obtained from any one of the plurality of heads. 2. The tracking control system according to claim 1, wherein a level difference signal between two types of difference frequency signals generated from a signal is sampled and held. (3) The playback head is composed of a plurality of heads that are selectively switched for each track, and the sample hold circuit samples and holds the level difference No. 46 during a period other than the playback head switching period. A tracking control method according to claim 1 or 2.