JPS60150255A - Automatic tracking device - Google Patents

Abstract

PURPOSE:To eliminate an error signal having 30Hz cycle which appears at a control signal for the tracking phase in a tracking controller using four types of pilot signals different in frequencies, by using a head switching pulse to produce an error erasing signal. CONSTITUTION:The pilot signal is sampled through an LPF15 for reproduction signals fed from rotary magnetic heads A and B. Then these reproduction signals undergo the balanced modulation through a balanced modulator 16. Thus the signals of frequency components 3fH and fH are obtained, and the differential is supplied to a BPF28 as a phase control signal S1. Then an error signal S2 having 30Hz cycle is extracted. The resistance division output of a head switching pulse Ps is supplied to a terminal of a subtractor 30 as an error erasing signal S3. Then a capstan motor 26 is driven by the signal S1 which is free from the signal S2.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a tracking device for a video tape recorder, and more specifically, 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 signals.

□ [Technical background of the invention] Conventionally, a helical scan type video tail coder (hereinafter referred to as V
When performing tracking control so that the rotating magnetic head accurately scans the recording track (video track) in the TR, a control signal recorded on the tape is used. 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 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, in general, the phase control of the control signal is not fixed to a constant value, but a tracking polymer is provided that can vary the phase stability point of the control signal, and by adjusting this, it is possible to It also ensures tape compatibility.

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 kinds of motherboard signals of different frequencies together with the video signal on the video trunk, and when playing back, the playback signal is used to move the rotary magnetic head to either the front or back of the video track to be scanned. There is a device that detects whether there is a deviation and controls 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 rotary magnetic head using four different frequency signals, the variation in the mounting height between the two rotary magnetic heads (J? Two comparison signals for detecting the tracking phase are extracted from the balanced modulation output of the Ilot signal (details will be described later).
Due to variations in the characteristics (gain vs. frequency characteristics) of the filter, the control signal (hereinafter referred to as phase control signal) of the APC (automatic phase control) loop that controls the tracking phase may have a signal component with a period of 30 Hz (hereinafter referred to as error signal). ) will occur.

As a result, uneven rotation of 30'H2 cycles occurs in the motor that is controlled by the servo loop, that is, the casostan motor. As a result, 30 Hz jitter occurs in the reproduced video signal, and wow and flutter in the audio signal worsens.

Considering mass production, it is extremely difficult to eliminate such defects, including changes over time, through component precision and adjustment alone.

[Purpose of the invention]

The present invention has been made in order to cope with the above-mentioned circumstances, and provides an automatic tracking device capable of removing an error signal of 30I (z period) occurring in a tracking phase control signal with a simple configuration. With the goal.

[Summary of the invention]

This invention focuses on the fact that the phase difference between the head switching pulse and the error signal is 0° or 180°, and generates an error cancellation signal by controlling the gain of the head switching pulse according to the amplitude detection output of the error signal. The error signal is removed by combining this error cancellation signal with a phase control signal that controls the tracking phase of the rotating magnetic head.

[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 four 29-lot signals mentioned above.
This figure shows an example of a tape recording pattern. In this case, there is no conventional control track. Tape 1 has video track 2,
．． 9, 4, 5, 6, 7, . . . are formed in order. Tracks 2.4.6 are recorded by one of the two rotating magnetic heads (head A), and tracks 3 and 5.7 are recorded by the other head (head B).
It was recorded in These tracks have a video signal along with the NoJ? A pilot signal is recorded in a superimposed manner, and as described above, this pilot signal is composed of four kinds of /firoy) signals of different frequencies and are recorded on a video track in a predetermined order. That is, tracks 2 to 7 have frequencies f1-f2fs, f<, ft, respectively.
, f2 (hereinafter f3 + fa + . . . ) pilot signals are 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 rotating magnetic head B scans, for example, track 5 as shown in the figure. At this time, this head B is on track 5.
Pilot signal P (f4
) (and video hinoki), pilot signals P(fa) of frequencies f3 and ft are generated from the trunks 4 and 6 on both sides, respectively.

P(fl) is reproduced (because the frequency of the pilot signal 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 Fig. 2,
Create a phase control signal for tracking control.

Next, the configuration and operation of the circuit shown in FIG. 2 will be explained. In FIG. 2, the portion surrounded by a broken line is a feature of the present invention.

First, a description will be given of the part that generates the phase control signal for controlling the tracking phase of the rotary magnetic head based on the reproduced signal.

The signals reproduced from the rotating magnetic heads A and B are sent to the reproduction preamplifier 12 via rotating transformers llh and llb, respectively.
a, 12b, and is further input to the switch SWl, which is opened and closed by the head switching i4 pulse P8 inputted from the terminal 10. Amplifier 1 corresponding to heads A and B during tracking is output from switch SWl.
The outputs of 2a and 12b are taken out alternately, and this output is A
The signal is input to an amplifier 13 for GC (automatic gain control), and its amplitude is adjusted. The output signal of this amplifier 13 is passed through an equalizer amplifier 14 to a low bus filter (LPF').
) J s is supplied, and the f ilot signal is extracted. This mother pilot signal output is the AGC detection circuit 1
7.

Furthermore, this f-irot signal output is transmitted to Hera PA during recording.
The converted girot signal, which has the same frequency and the same order as the girot signal supplied to the terminal 161, is supplied to the terminal 161.
The signal is manually input to a balanced modulator (BM) 16 for balanced modulation. At this time, as shown in the table, if the frequencies of the mother pilot signals P(fx) to P(f4) are determined (naturally, the converted pilot signal also has a frequency of each of these mother pilot signals). from this BMI 6 a signal with frequency components of 3fH and 9 is obtained.

=9- For example, when head B is scanning track 5 as shown in FIG. 4.6, the frequencies fa and fl, respectively.
Gwilot signal P (fa)' t 'P' (ft
). At this time, as the converted/9-irot signal, a converted/f-irot signal having the same frequency as the pilot signal P (f4) is supplied from the terminal 161 to the BMI 6 (this is the case because of the servo effect).

Therefore, the above frequency components are synthesized from 8M16,
In this case, the frequency component 1fa corresponding to the advance of the tape
The frequency component lf corresponding to the fll signal and the tape delay
4? sl signal is obtained. Note that the frequency component corresponding to the scanning of track 5 is 0 (f4 f4=o)
. The level of the signal having frequency components of 3fH and fH from BMI 6 has a magnitude proportional to how much the scanning of head A or B has shifted to the left or right. In other words, depending on whether the scanning of heads A or B (where 9 is the horizontal synchronization frequency) is delayed or advanced, the level of one of the signals having frequency components of 3fH and 9 will be higher than the other. . As you can see from the table, head A
The frequency components corresponding to the delay (or lead) in and B are inverted, but this can be done by switching the head switching/arm pulse (pm) IC and the switch SW2, as will be described later.

The output of BMJ 6 is a band/pass filter (BPF) to extract the 9 and 3 fH frequency components, respectively.
Js, J9 will be operated manually. The signals having frequency components of 9 and 39 extracted by the BPF 113 and J9 are subjected to level detection as comparison signals by level detectors 20 and 21, respectively, and are input to the switch SW2. As mentioned above, this switch Sw2 has reversed frequency components corresponding to the lead and lag in heads A and B, so
It is used for switching. In other words, when head A reproduces b, the frequency component corresponding to the advance is lfH (delay is 3fH), and when head B is reproducing it, it is 3fH (delay is fH), so this Switch 5IIV is 3fH when head A is playing.
The output of BPF 19 for BPF 19 is connected to the 10 terminal of subtraction type voltage comparator 22, and the output of BPF J B for 9 is connected to voltage comparator 2.
When head B is performing playback, it is switched so that it is manually input to one terminal of head B.

The voltage comparator 22 compares the signal levels of the frequency component of 1fH*37H, and outputs the difference.

This difference output is supplied as a phase control signal (Sl) to a capstan motor 26, which will be described later, and by opening the rotational phase of this motor 26, the tracking phases of the heads A and H are controlled.

The phase control signal (Sl) includes an error signal (S2) with a period of 30 Hz due to variations in the mounting level difference between the heads A and B, variations in the characteristics of the Pandox filters 18 and 19, and the like. The circuit surrounded by the broken line is the phase control signal (81)
Remove the error signal (S2) from. The phase control signal (St) from which the error signal (S2) has been removed is passed through the loop filter 23.
, mixer 24, and motor drive amplifier 25 to the capstan motor 26 as a motor control signal. As a result, APC is applied to the capstan motor 26 that drives the chip so that the phase control signal becomes the reference level, and the rotating magnetic heads A and B are accurately aligned with their own Bill.
Now scans Odorak. That is, the chive feed is controlled so that the two signal levels having the frequency components of fH and 3fH are the same or have a constant voltage difference. Note that 27 is an AFC (automatic frequency control) discriminator that detects the rotational frequency of the capstan motor 25 and outputs a control signal to set it to a predetermined value. This AF
The C valve side discriminator 27 force signal is added to the phase control signal (Sl) in the mixer 24 and is supplied to the capstan motor 25.

Next, the configuration and operation of the portion surrounded by broken lines, which is a feature of the present invention, will be explained.

The phase control signal (Sl
) is a band with a center frequency of 30Hz! Filter (B
PF ) 2 B and is also supplied to the ten terminal of the subtracter 30 via the resistor 29 . BPF RB is a 30Hz period error signal (
S2) is extracted and given to the amplitude detection circuit 3J to detect its envelope. This detected output is shaped into a rectangular wave by the waveform shaping circuit 32 and then supplied to one input terminal of the polarity discrimination circuit 33.

The head switching signal (PI) applied to the terminal 10 is supplied to the other input terminal of the polarity discrimination circuit 33, and the polarity discrimination circuit receives the error signal (82) from the head switching signal (P8). Determine whether the polarity is the same as that of the polarity. According to this determination result, the movable contact (b) of the switch SW3, which was in the center position (ax), is connected to the position (a2) or (a3).

Position (a2) is connected to the terminal IO via a resistor 34, and position (a3) is connected to the terminal 10 via a resistor 35 and an inverter circuit . Also,
The movable contact (b) is connected to one terminal of the subtracter 30, and the field effect transistor fi (FET) sy
It is grounded via the drain-source current path of.

Error signal (Sl) and head switching pulse (P8
) have the same polarity (phase difference O0), the movable contact piece (b) of the switch SWs is connected to the position (a2). As a result, head switching Yarus (P8) is part 1
Well, it is divided by the resistor 34 and the drain-source resistance of the FET 37. This resistance-divided output is supplied to one terminal of the subtracter 30 as an error cancellation signal (S3), and is subtracted from the phase control signal (Sl). Conversely, the error signal (
When the head switching signal (Sl) and the head switching signal (P,) have opposite polarities (phase difference of 180°), the movable contact piece (b) of the switch '8W' is connected to the position (&3). Therefore, the head switching pulse (ps) is inverted by the inverter circuit 36, and the head switching pulse (ps) is inverted by the inverter circuit 36.
The signal is divided by the drain-source resistance of 7 and is supplied to the subtracter 30 as an error cancellation signal (S3).

As described above, an error cancellation signal (S3) having the same polarity as the error signal (Sl) is obtained, and its amplitude is
In order to match that of the error signal (Sl ),
The drain-source resistance of the FET 37 is controlled according to the amplitude of . That is, the detected output of the amplitude detection circuit 31 is supplied to one terminal of an error signal amplification circuit 40 formed by a differential amplifier □ via a dyne adjustment variable resistor 38 and a resistor 39, and is amplified by this error signal amplification circuit 40. Afterwards, it is supplied to the dart of FET 37. As a result, the Dreyley-to-source resistance of the FET 37 is controlled according to the amplitude of the error signal (Sl), and the amplitude of the error cancellation signal (S3) is matched to that of the error signal (Sl). As a result, a phase control signal (St) from which the error signal (Sl) has been removed is obtained from the subtractor 3°, and this drives the canostan motor 26, so that the rotational irregularity of the capstan motor with a period of 26,030 Hz is eliminated. It disappears.

Note that the variable resistor 38 is for adjusting the dyne of the error signal canceling loop shown in the broken line.

In addition, 4J is a feedback resistor, and (Vb) is the error signal amplification circuit 4.
This is the bias voltage supplied to the 0 terminal.

As detailed above, this implementation sequence focuses on the fact that the head switching f pulse (P, ) and the error signal (Sz) have a phase difference of 0° or 180°, and the head switching f pulse (P + r ) is used to eliminate the error signal (S3
). Therefore, the error signal (Sl) can be removed without providing an adjustment means to remove the error signal (Sl) while increasing the precision of the parts.
Even in mass production, video jitter and o
7- - It is possible to prevent deterioration of wow and flutter in the DIO signal.

Note that the tracking phase of the heads A and B can also be controlled by controlling the rotational phase of the cylinder f motor that rotationally drives the cylinder in which the heads A and B are installed, but the present invention can also be applied to such a system. Of course.

In addition, in the previous embodiment, the error signal (Sl) is
) has been described, however, the error signal (Sl) may be erased by addition processing, and in this case, the switching of the switch sW3 may be reversed from that in the previous embodiment.

Further, in the previous embodiment, a case was explained in which a three-point switch was used as the switch SW3.
, a3 may be used. In this case, the signal line (A) (second
(see figure) without providing posisilane (a2) or (a3
) may be used as the other input of the polarity discrimination circuit 33 at the time of polarity discrimination.

Furthermore, the drain-source current path of terminal 10 and FET 37 is connected only by a resistor, and this connection point and subtractor 3
0, the switch SW3 and the inverter circuit 36 may selectively form a loop that directly connects the connection point to one terminal of the subtracter 30 and a root that connects the connection point via the inverter circuit. good. Now, get the error cancellation signal (S3) of the same polarity as the head switching pulse (P8) at the above connection point, and then set this polarity appropriately according to the polarity of the error signal (S2) and subtract it. Vessel 3
It is supplied to one terminal of 0.

Note that even if the polarity of this signal (S3) is set after controlling the division r-in of the error cancellation signal (S3) by the resistor as described above, it is also possible to Even if the polarity of the error cancellation signal (S3) is set to control the division dyne, if a two-point switch such as the one described above is used as the switch SW3, the polarity of the error cancellation signal (S3) will be , movable contact (
It goes without saying that it is necessary to decide which of positions a2 and a3 to connect b) to. That is, in the initial state, it is necessary to set an initial value for the switch SW3, for example, so that the comparison is always made in positive phase.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an automatic tracking device that can remove a 30 Hz cycle error signal that occurs in a tracking phase control signal with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the recording and recording of 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. 28...BPFl 29.34, 35.39...Resistor, 30...Subtractor, 3...Amplitude detection circuit, 32
...Waveform shaping circuit, 33...Polarity discrimination circuit, 36.
...Inverter circuit, 37...FET, 38...Variable resistor, 40...Error signal amplification circuit, 4...Feedback resistor. Applicant's agent Patent attorney Takehiko Suzue 21- Figure 1□B

Claims (1)

[Claims] At the time of recording, a video signal and a pilot signal are recorded onto a magnetic tape by two rotating magnetic heads, and during playback, a video signal and a pilot signal are recorded from the magnetic tape by the two rotating magnetic heads. In an automatic tracking device that controls tracking phases of the two rotating magnetic heads based on reproduced pilot signals, a motor capable of controlling tracking phases of the two rotating magnetic heads; a phase control signal generating means for generating a phase control signal for controlling the tracking phase of the two rotating magnetic heads and supplying it to the motor; and a filter for extracting a 30 Hz period error signal from the phase control signal. means, amplitude detection means for detecting the amplitude of the error signal extracted by the filter means, and switching control for selecting the reproduction output of the rotary magnetic head that is tracking the magnetic tape among the two rotary magnetic heads. the gain of the head switching signal used for the filter is controlled according to the detection output of the amplitude detection means; a polarity determining means for determining the polarity of the error signal extracted by the means; and a polarity determining means for determining the polarity of the error signal extracted by the means; and combining means for removing signals.