JPS6079551A - Automatic tracking device - Google Patents

Abstract

PURPOSE:To always obtain an optimum tracking phase of a rotary magnetic head by varying gradually a gain of a motor control signal in a prescribed period determined in advance, also envelope-detecting a reproducing output in this period, and providing this detecting output to the motor control signal. CONSTITUTION:A CPU of a microprocessor 28 executes a processing for outputting a gain control signal for varying gradually a gain of a motor control signal outputted from an adder 24 is a picture muting period in case a reproducing operation is started. This gain control signal is converted to an analog signal by a D/A converter 29, and thereafter, supplied to (-) terminal of an adder 26. As for this adder 26, when a level of the gain control signal is varied gradually, the gain of the adder 26 to the motor control signal supplied to its (+) terminal is varied. As a result, an output level of the adder 26 is varied gradually, a rotational phase of a capstan motor M is varied gradually, and a tracking phase of rotary magnetic heads A, B is also varied gradually.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a tracking device for a video tape recorder. The present invention relates to a tracking device for a video tape recorder that tracks a rotating magnetic head based on information.

[Technical background of the invention]

Conventionally, in a helical scan video tape recorder (hereinafter referred to as a VTR), control signals recorded on the tape are used to perform tracking control so that the rotating magnetic head accurately scans the recording track (video track). . That is, during recording, a control signal is recorded on the side edge of the tape along its length, and during playback, tape feeding is controlled so that the phase of this control signal matches the phase of the reference signal. In this way, the rotating magnetic head can accurately scan the video track. However, if the recording position accuracy of the control signal or the recording position of the video track is insufficient, or if the track linearity is poor, tracking may not be achieved when the tape is played back between different devices.

Therefore, it is generally not necessary to fix the phase control of the control signal to a constant value, but instead of using racking, which allows the phase stability point of the control signal to be varied. By installing a tape tape and adjusting the tape, tapes can be used interchangeably with different devices.

By the way, for users who don't know how to adjust the tracking volume or who find it troublesome, there is a V that can automatically adjust tracking.
TR has been proposed. One method is to superimpose and record four different frequency signals on the video track together with the video signal, and when playing back, use the playback/mother signal to scan the front and back of the video track that the rotating magnetic head should scan. Some devices detect which direction the head is deviated from and control the tracking phase of the head based on the detected output.

[Problems with background technology]

However, in the device that controls the tracking phase of a rotating magnetic head using the four types of motherboard signals of different frequencies described above, tracking There may be a positional offset and it may not be possible to center the rotating magnetic field on the track.

The above-mentioned variations in mechanical performance and accuracy include, for example, differences in mounting level between two rotating magnetic heads, variations in track width of the rotating magnetic heads, and variations in track pitch difference. Furthermore, variations in electrical precision and accuracy include variations in the dynes of the rotor IJ lance, regeneration preamplifier, band/pass filter, and frequency characteristics of the equalizer amplifier.

[Purpose of the invention]

This invention was made to deal with the above situation, and V
It is an object of the present invention to provide an automatic tracking device that can always obtain the optimal tiger and king phases of a rotating magnetic head regardless of variations in mechanical and electrical performance and precision of each part of a TR.

[Summary of the invention]

This invention gradually changes the gain of the motor control signal obtained based on the regenerated pilot signal within a predetermined period, performs envelope detection on the regenerated output during this period, and The gain at the point where the detected output is maximum is given to the motor control signal after the predetermined period has elapsed.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 shows a VTR equipped with an automatic tracking device that performs tracking control using the above four A' pilot signals.
This shows an example of tape recording iR turn. In this case, there is no traditional control track. Tape 1 has video track 2 t 3 t 4 t 5 t 6
t 7 , . . . are formed in order. Tracks 2 and 4.6 were recorded by one of the two rotating magnetic heads (head A), and track 3 #
s t 7 is recorded by the other head (to, do B). These tracks are recorded with the video signal superimposed with the Nokilot signal, and this i
As mentioned above, the Z-irot signal has four different frequencies.
The pilot signals are recorded on the video track in a predetermined order. That is, tracks 2 to 7 have frequencies efl and fz, respectively.

fs = f4-fx, fz (hereinafter f3 yf<t・
) is recorded superimposed on the video signal. Note that arrow A indicates the tape running direction, and arrow opening indicates the scanning direction of the rotating magnetic head.

During reproduction, the rotary recording head B scans, for example, track 5 as shown in the figure. At this time, this head B is on track 5.
The frequency f4 recorded in Gwilot Tsukuda P(f
4) (and the video signal) and simultaneously reproduce pilot signals P(fs) of frequencies af3-fl from tracks 4 and 6 on both sides.

P(fx) is reproduced (pilot) (because the frequency of No. 1 is low and the influence of azimuth loss is small, the pilot signal of the adjacent track is also reproduced at the same time). Next, these signal outputs are detected by the tracking device shown in Figure 2,
Create a motor control signal for tracking control.

Next, the configuration and operation of the circuit shown in FIG. 2 will be explained.

In addition, the part surrounded by the broken line in FIG. 2 is the part that characterizes the present invention.

First, the part that controls the tracking phase of the rotary magnetic head based on the reproduced pilot signal will be explained.

The signals reproduced from the rotary magnetic heads A and B are sent to a reproduction preamplifier 12 via rotary transformers 11a and 11b, respectively.
a, 12b, and is further input to a switch SWi which is opened and closed by a head switching pulse P input from a terminal 10. The outputs of the amplifiers 12 a r 12 b are alternately taken out from the switch SW1, and these outputs are used as the outputs of the amplifier 1 for AGC (automatic gain control).
3 and its amplitude is adjusted. This amplifier 13
The output signal is supplied to a low pass filter (LPF) 25 via an equalizer amplifier 14, and a pilot signal is extracted. These output signals are supplied to the AGC detection circuit 17. Further, this /(' pilot signal output is supplied to heads A and B during recording.) A balanced modulator ( B
M) 16 for balanced modulation.

At this time, as shown in the table, Pilot No. 46 P (ft)
If the frequencies of P(f4) to P(f4) are determined (the converted i4 pilot signal naturally has a frequency equal to each of these pilot signal frequencies), then this BMI6
From this, signals with frequency components of 3fH and fH are obtained.

For example, when head B is scanning track 5 as shown in FIG. , 6, respectively, to reproduce pilot signals P(fs) and P(fl) of frequency fs=fl. At this time, the conversion pilot signal p (
The converted pilot signal with the same frequency as f4) is connected to terminal 16.
1 is supplied to BMI 6 (this happens because the tape is applied). Therefore, the above frequency components are synthesized from the BMI 6, and in this case, a signal of the frequency component 1f4-ftl corresponding to the advance of the tape and a signal of the frequency component 1f4-fsl corresponding to the delay of the tape are obtained. Note that the frequency component corresponding to the scanning of track 5 becomes zero (f4f<=O). BMI 5 to 3 f
. That is, depending on whether the scanning of head A or B is delayed or advanced, the level of one of the signals having frequency components of 3/H and fH will be higher than the other. As you can see from the table, the frequency components corresponding to delays (or advances) are reversed in Do A and B, but this is due to the head switching/Grus kBMI 6 as will be explained later.
The outputs are input to pandox fill voice (BPF) 1g and J9 for extracting the frequency components of fH and 3fH, respectively. BPF l & and f taken out at 19
The signals having frequency components of
2 is input.

As described above, this switch SW2 is used for switching between heads A and B since the frequency components corresponding to the lead and lag are reversed. That is, when playing back with head A, the frequency component corresponding to the advance is 1f■ (the delay is 3'fH), and when playing back with head B, the frequency component corresponding to the advance is 0. H (Delay &! The output of BPF JB is switched to be input to one terminal of the voltage comparator 22, so that when head B is reproducing, it is just the opposite. 1fn in the voltage comparator 22;

The level of 4it of the frequency component of 3 fH is softened,
The difference is output.

This phase difference output is passed through the loop filter 23 to the adder 2.
4. Then, the adder 24 discriminates the rotational frequency of the capstan motor M, and adds it to the output signal of an AFC (automatic frequency control) discriminator 25 for setting it to a predetermined value. (described later) is supplied to the motor M as a motor control signal via a motor drive amplifier 27. As described above, since the APC (automatic phase control) of the capstan motor that drives the tape is applied so that the phase difference output becomes the reference level, the tracking control is performed so that heads A and B accurately scan their own video tracks. be done. That is, always fH and 3f
The tape is fed so that the two signal levels having the H frequency component are the same or have a constant voltage difference.Next, the structure and operation of the characteristic portion of the present invention will be explained. 28 is microzorohi. This microprocessor 28
CPU (without 1 vote) outputs from the adder 24 during the image meet period when the playback operation is started →
- Execute processing to output a gain control signal for gradually changing the gain of the data control signal. This gain-control signal 4'd is a digital code signal, and after being converted into an analog signal by the D/A4 converter 29, it is supplied to one terminal of the adder 26. : Since this adder 26 has a differential amplifier configuration, when the level of the J gain control signal gradually changes,
The gain of adder 26 for the motor control signal being supplied to the Some+ terminal changes. As a result, the output level of the force i calculator 26 gradually changes, and the rotational phase of the canstan motor M gradually changes. .

As a result, the tracking phases of the rotating magnetic heads A and H also gradually change. 1 At this time, the reproduced output signal given via the switch SW1 is amplified by the amplifier 30, and then sent to the envelope'
K-wave device? Envelope detection is performed at I. This detection output is A/1) (analog/digital) converter 32
After the signal is converted into a digital signal, the microprocessor 2
This microprocessor also has 28 CPUs
The data is stored in RAM (not shown) in the memory. The CPU further detects the maximum value of the detected output and determines the level of the gain control signal when the maximum output is obtained. Then, when the image mu snoring period ends,
The gain control signal of the determined level is constantly supplied to the adder 26 via the D/A converter 29, and the gain of the motor control signal is set to the gain when the envelope detection output reaches the maximum.

The point where the envelope detection output of the reproduced output signal is maximum is the rotating spider head A.

When B is scanning the center of the track. Therefore, if the gain of the motor control signal at this time is given to the motor control signal after the end of the image mute period, the tracking phase will change when the motor control signal obtained based on the reproduced pilot signal is followed. Even if an offset would occur in , no offset occurs.

Note that the tracking phase during the image mute period is controlled in both the leading and trailing directions.

As detailed above, according to the present invention, the gain determined based on the maximum envelope detection output when the gain of the motor control signal formed from the regenerated pilot signal is gradually changed forcibly is given to the motor control signal. I did it like this,
Mechanical and electrical performance and accuracy vary, and even if an offset would occur if the tracking phase was determined only from the regenerated pilot No. 1, no offset occurs. This eliminates the need to require higher precision than necessary for the components of the VTR, which is advantageous in terms of VTR manufacturing costs and the like.

In the previous embodiment, a case has been described in which the gain of the motor control signal is adjusted at the output stage of this signal, but the gain may be adjusted during the generation process. For example, as shown by the broken line (4) in FIG.
It may also be controlled quickly.

Furthermore, the operation of setting the gain of the motor control signal may be performed during a period other than the image mute period.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an automatic tracking device that can always obtain the optimum tracking phase of a rotating magnetic head regardless of variations in mechanical and electrical performance and precision of each part of a VTR.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing nine turns of tape recording in a VTR equipped with an automatic tracking device, and FIG. 2 is a circuit diagram showing one embodiment of the automatic tracking device according to the present invention. 26... Adder, 28... Microprocessor 1.
29...D/A converter, 30...J.8 width converter,
31... Enperoso detector, 32... Inverter. Applicant's agent Patent attorney Takehiko Suzue Figure 1□B

Claims (1)

[Claims] At the time of recording, a video signal and a pilot signal are recorded on a magnetic tape by a rotating magnetic head, and at the time of reproduction, a video signal is reproduced from the magnetic tape along with the video No. 11 by the rotating magnetic head. In an automatic tracking device that adjusts the tracking phase of the rotating magnetic head by 1ii31+t41 based on a signal, a capstan motor for running the magnetic tape and a pilot signal reproduced by the rotating magnetic head are used. a motor control means that outputs a motor control number 43 that controls the rotational phase of the capstan motor; and a gain variable means that can gradually change the gain of the motor control side 1 signal during a predetermined period of time. and envelope detection means for detecting an envelope of the reproduction output of the rotating magnetic head during the predetermined period; detecting a maximum value of the detection output of the envelope detection means, and setting a gain set by the gain variable means when the maximum value is output. and gain fixing means for setting the gain determined by the gain determining means to the motor control signal after the predetermined period has elapsed.