JP2565204B2 - Tracking device for diagonal tracks - Google Patents

Description

The present invention relates to a tracking device for an oblique track such as a VTR, and particularly to a tracking servo system using a tracking pilot signal.

[Outline of Invention]

In a servo system that forms a tracking error voltage based on a four-frequency pilot signal cyclically recorded on a diagonal track in a four-track sequence, a back lock is detected by inserting a pilot signal for back lock detection into a reference pilot signal. When a back lock is detected by providing detection means, the four-frequency sequence of the reference pilot signal is reduced to 1/4.
This is an oblique track tracking device in which the error voltage is forcibly generated by advancing or delaying the phase by one track, and the tracking position of the rotary head is rapidly moved from the back lock position in the track arrangement direction.

[Conventional technology]

In VTR, 4 heads are used and the head drum diameter is 2/3
There is known a small-diameter drum system in which the tape winding angle is 270 °, the drum rotation speed is 45 rotations (3/2 times 30 rotations), and the recording format is kept the same as usual.

On the other hand, an ATF (Auto Track Findin) that cyclically records a tracking pilot signal of 4 frequencies in a cycle of 4 tracks
A tracking servo system called g) is known,
It is also used in the VTR of the 4-head small diameter drum system.

ATF servo 4-head VTR has 4 heads and 4 heads
Since the frequency pilot signals have a one-to-one correspondence, the same head corresponds to recording and reproduction for each of the four tracks. Therefore, the self-recording / reproducing (recording / reproducing with the same VTR) causes little image quality deterioration.

[Problems to be solved by the invention]

With the ATF servo system, there is one servo lock point for every four tracks, so locking is relatively slow. In particular, the tracking error voltage at the lock point is zero, and the tracking error voltage becomes the maximum of negative and positive in correspondence with the track deviation of +1 track (front in the tape running direction) and -1 track (back in the tape running direction). If the deviation increases, the error voltage becomes minute, and the tracking error voltage becomes zero at the point of the track deviation of ± 2 tracks.
This ± 2 track shift position is a pseudo lock point called back lock, and it is not locked at this point,
Since the error voltage is zero, the reproduction trace position moves very slowly toward the regular lock point two tracks away.

In order to increase the servo lock speed, it is detected that there is a track deviation near the pseudo lock point, and the reference pilot signal of 4 track cycles of 4 track cycles is added for 2 tracks so that this point becomes the normal lock point. It has been proposed to shift the sequence and simultaneously shift the head switching sequence of 4 heads sequentially by 2 heads (Japanese Patent Application No. 62-68720).

According to this method, the lock points are substantially two in four tracks, and the lock-in speed of the servo system is increased. Further, when the pseudo lock point is converted into the lock point, the heads are switched at the same time and the scanning order of the 4 heads is shifted by 2 heads, so that the recording head and the reproducing head correspond to the same track. Therefore, the image quality does not deteriorate during self-recording.

However, if the scanning order of 4 heads is shifted by 2 heads, the phase of the reproduced video signal jumps by 2/3 fields, which causes a problem of disturbing the monitor image.

In view of this problem, the present invention aims to increase the lock-in speed of the tracking servo without causing the reproduction phase jump.

[Means for solving problems]

Tracking device of an oblique track of the present invention, the rotary head 1a, 1b, 2a, 4 frequency reference pilot signal in synchronization with the reproduction tracing slant track by 2b (f ₁ ~f ₄₎ pilot signal generating circuit for circulating generate (Pilot signal generator 10 and switch circuit 8), track deviation detection circuit 21 for deriving a tracking error voltage based on a reproduction signal of a pilot signal of four frequencies cyclically recorded by repeating four tracks and the reference pilot signal. And a pilot signal for detecting the backside lock is inserted into the reference pilot signal, and the tracking error voltage corresponding to the position of the interleaved pilot signal is taken in to detect the backside lock generated by a two-track phase difference with respect to the normal servo lock point. When the back lock is detected by the detection means (determination circuit 25) for performing detection, A control signal is supplied to the pilot signal generation circuit to set the four-frequency sequence of the reference pilot signal to the advance or lag phase by 1/4 (one track) at a time, and the tracking position of the rotary head is rapidly tracked from the back lock position. Control circuit 11 for moving in array direction
And

[Action]

Even if the tracking voltage is almost zero in the back lock state,
By shifting the phase of the reference pilot signal by 1/4, an error voltage equivalent to a shift of one track is generated.
Therefore, the servo system shifts from the static state where the error voltage is zero to the dynamic state, and the tracking phase rapidly moves to the normal lock point.

〔Example〕

FIG. 1 shows a schematic block diagram of a tracking servo system of a 4-head small-diameter drum VTR to which the present invention is applied. This VT
R is four heads 1a and 2 for every 90 ° as shown in FIG.
A, 1b, and 2b are held on the rotary head drum 3, and 180a opposite pair 1a and 1b have a positive azimuth angle (+) and 2a and 2b have a negative azimuth angle (-). The magnetic tape 4 is wound around 270 °, and the drum 3 rotates at 45 times / second. Heads 1a (+), 2a (-), 1b every 3/4 rotation (270 °)
Azimuth recording is performed on tracks T1a, T2a, T1b ... As shown in FIG. 3 by sequentially switching (+) and 2b (-).

This VTR is 4 as shown in the recording format in Fig. 3.
A tracking type capstan phase servo called frequency ATF (Auto Track Finding) is used. That is, the continuous tracks on the magnetic tape 4 is cyclically recorded by superimposing a 4-frequency pilot signals f ₁ ~f ₄ of the tracking servo to the video signal in the 4 tracks cycles. f _{1 to} f ₄ are 102, 116, 160 and 140 KHz, respectively.
During reproduction, the phase of the capstan motor is controlled so that the crosstalk difference between pilot signals from both sides of the scanning track is eliminated.

The reproduction signal reproduced by each head 1a, 1b, 2a, 2b at the time of reproduction is led to the head changeover switch circuit 6 through the reproduction amplifiers 5a to 5d, and sequentially based on the head changeover pulse which is changed every 270 °. It is selected and supplied to a reproduction process unit (not shown). The output of the head switching circuit 6 is given to the low-pass filter 7, and the frequency band component of the pilot signal is extracted. The extracted pilot signal is multiplied by the reference pilot signal of the sequence f _{1 to} f ₄ supplied from the switch circuit 8 by the multiplier 9 to obtain the frequency difference component between the reproduction signal and the reference signal. The components of the frequency difference in the multiplication calculation force are the following two types.

Δf _A = | f ₁ −f ₂ | = | f ₃ −f ₄ | = 14 (KHz) Δf _B = | f ₂ −f ₃ | = | f ₄ −f ₁ | = 44 (KHz) Note that the reference pilot signal Is generated by the pilot signal generator 10, and the control signals SEL1, 2 of the output of the switch control circuit 11
Thus, the switch circuit 8 sequentially selects and derives in a predetermined sequence.

If the correct scan track corresponding to the heads 1a and T _1a, the frequency difference component Delta] f _A of the output of the multiplier 9 crosstalk component from the right adjacent track T ₂ b, Δf _B cross from the left adjacent track T _2a It is the talk component. Therefore Δf _A
The amount and direction (left and right) of the track deviation can be known from the level difference between the component and the Δf _B component.

These difference frequencies Δf _A and Δf _B are converted to the bandpass filter 1
A tracking error signal is obtained by separating and extracting in 2 and 13, detecting in DC conversion circuits 14 and 15, and subtracting the DC output in subtractor 16. Since the polarity of this error signal is inverted every time the scanning track changes, a signal passing through the inverter 17 and a signal not passing through it are alternately selected by the switch 18 which is switched by the switching pulse ATFSW, thereby performing synchronous rectification. To do. The output of the switch 18 shows a left shift if the polarity is positive, a right shift if the polarity is negative, and becomes zero if there is no shift. By supplying this error voltage to the capstan motor through the sample hold circuit 19 and the amplifier 20, reproduction trace without tracking error is performed.

From the above low pass filter 7 to the sample and hold circuit
Up to 19 constitutes a track shift detection circuit 21.

FIG. 4 is a graph showing the relationship between the tracking error voltage and the track deviation. Considering one track T _1a , the tracking error voltage is zero when the head 1a (reference pilot f ₁ ) is tracing this track. The servo system is locked. When a track shift occurs with respect to the lock point Q, positive and negative track error voltages are generated according to the left shift and the right shift, and the servo loop operates so as to return to the lock point Q.

When the track deviation is ± 1 track pitch (T _p ),
The error voltage becomes the maximum of positive and negative, and when the track deviation further increases, the error voltage decreases, and the error voltage becomes zero again with the deviation of ± 2 track pitch. This is the back-locked state described above. For example, as shown in FIG. 4, the head 1a (pilot
f ₁ ) traces track T ₁ b (f ₃ ) which is two tracks off. This back lock point Z is an unstable point, and if it deviates even a little from this point, the error voltage increases toward the lock point. However, since the error voltage gradually increases from zero, it takes a long time to lock in.

Therefore, it is detected that there is a trace position in the vicinity of the back lock point Z, and when it is detected, the following processing is performed to rapidly increase the error voltage.

The back lock detection can be easily performed by inserting a pilot signal for back lock detection into a reference pilot signal, as shown in FIG. 5B. That is, the reference pilot signals f ₁ , f _2, ... Are sequentially supplied from the switch circuit 8 of FIG. 1 to the multiplier 9 in synchronization with the head switching pulse of FIG. 6A, but as shown in FIG. 6B. The pilot signal P _B left-shifted by one track is inserted into each pilot signal P _A. The tracking error for this interpolated pilot signal P _B is
As shown in B of FIG. 4, the error voltage A appears one track to the left with respect to the original error voltage A.

Therefore, the sample-hold circuit 19 for tracking error shown in FIG.
The TSA is supplied to take in the original error voltage A and lead it to the capstan servo system. Further, the sample and hold circuit 22 provided in parallel with this is supplied with the sample and hold pulse TSB of FIG. 6D corresponding to the interposing pilot position to take in the error voltage B.

Error voltage B sample and hold output is comparator
23 and is compared with the comparison level rf2 shown in FIG. Since it is known from the comparison output S2 of the comparator 23 that there is a trace position near the back lock, S2 is supplied to the switch control circuit 11 to change the phase of the control signals SEL1 and SEL2, and the switch circuit 8 outputs it to the multiplier 9. The reference pilot signal P _A (and the interleaved pilot signal P _B )
As shown in FIG. D, the track is shifted to the left by one track from the phase in FIG. 6B. That is, the circulation sequence is advanced by 1/4 (one track). As a result, the reference pilot frequency during the period traced by the head 1a is shifted to f ₂ .

Then, the tracking error voltage obtained from the sample hold circuit 19 of FIG. 1 appears to be shifted by one track to the right with respect to the error voltage A as shown by the chain line C in FIG. For this reason, as shown in FIG. 6C, the back lock state is set and the tracking error voltage is substantially zero, but a negative error voltage is generated as shown in FIG. 6E. As a result, the capstan motor is rapidly decelerated, so that the head 1a rapidly moves relative to the tape in the direction of the dotted line X in FIG. 4, and the pilot f _{2 of the} head 1a and the reproduction pilot f _{2 of the} track T _2a are separated. Toward the lock point Q ′ at which At the lock point Q ', the tracking error voltage C becomes substantially zero.

Interpolated pilot signal P _B for the error voltage C in FIG.
The error voltage corresponding to (1) appears at the left of one track and corresponds to FIG. 4A. The error voltage A is near the negative maximum near the lock point Q '. Therefore, in FIG. 1, the output of the sample hold circuit 22 corresponding to the interpolating pilot is compared with the comparison level rf1 shown in FIG. Comparison output S1 (ATF
The trace position of head 1a is tracked by the lock signal)
Since it is known to be T _2a , S 1 is supplied to the switch control circuit 11 so that the reference pilot signal P _A (and the interleaved pilot signal P _B ) derived from the switch circuit 8 to the multiplier 9 is fed to the sixth
Put it back as shown in Figure F (Pilot the head 1a to f ₁
Correctly correspond to).

Then, the tracking error voltage becomes the phase shown in FIG. 4A, and when the trace position is near the lock point Q ',
The error voltage obtained from the sample hold circuit 19 of FIG. 1 suddenly changes from a substantially zero level to the vicinity of the negative maximum as shown in FIG. 6G. As a result, the capstan motor is further decelerated, so that the head 1a moves in the direction of the dotted arrow X in FIG. 4 and quickly locks at the lock point Q on the track T _1a (pilot f ₁ ).

As described above, the track deviation is ±
Even if 2 tracks are generated, 4 frequency reference pilot signals will be 1
By shifting the phase for each track, the tracking error voltage can be forcibly generated and immediately moved to the regular lock point.

Therefore, by utilizing this principle, mutual phase adjustment can be performed in the field unit video editing using two VTRs. That is, the lock status of the servo system is compared with the comparator.
If the circulating phase of the reference pilot signal is phase-advanced or phase-advanced by one track while being detected by the determination circuit 25 composed of 23 and 24, the relative phase between the head and the track changes accordingly. . Therefore, for example, an edit servo system can be constructed in which the servo phase of the reproducing VTR is continuously variable with respect to the phase of the recording VTR, and mutual phase adjustment is performed while reading the time code for each field recorded on the tape.

〔The invention's effect〕

As described above, the present invention, when the back lock, which is a pseudo stable state of the servo system in which the error voltage is zero, is detected,
By shifting the sequence of the reference pilot signal by one track, an error voltage corresponding to the shift of one track is generated, and the servo system error voltage is shifted from the static state to zero to the dynamic state. Therefore, the tracking phase can be moved rapidly to the regular lock point,
It is possible to obtain a high-speed response servo circuit having a shorter lock-in time with a simple and reliable structure.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a tracking servo system of a 4-head VTR to which the present invention is applied, FIG. 2 is a schematic diagram of a 4-head drum device, and FIG. 3 is a recording format diagram showing a track arrangement on a tape. FIG. 5 is a graph of a tracking error voltage corresponding to a track deviation, FIG. 5 is a time chart showing a 4-frequency sequence of a reference pilot signal and a sample phase of an error voltage, and FIG. 6 is a time chart showing a sequence control of a reference pilot signal. is there. In the reference numerals used in the drawings, 1a, b, 2a, b ... rotary magnetic head 3 ... rotary head drum 4 ... magnetic tape 8 ... switch circuit 10 ... pilot signal generator 11 ... switch control circuit 21 ...... Track shift detection circuit 25 ・ ・ ・ Judgment circuit.

Claims (1)

(57) [Claims] 1. A pilot signal generation circuit for cyclically generating a reference pilot signal of 4 frequencies in synchronization with a reproduction trace of an oblique track by a rotary head, and a reproduction signal of a pilot signal of 4 frequencies cyclically recorded by repeating 4 tracks. And a track deviation detection circuit for deriving a tracking error voltage based on the reference pilot signal, and a pilot signal for detecting the back lock on the reference pilot signal, and the tracking error voltage corresponding to the position of the interleaved pilot signal. When the back lock is detected by the detecting means which takes in and detects the back lock generated by the two-track phase difference with respect to the normal servo lock point, the control signal is supplied to the pilot signal generating circuit. , 4 frequency sequence of the above reference pilot signal 1/4 (for one track) In the Mimatawa lag phase, a tracking device the oblique tracks and a control circuit for moving rapidly track arrangement direction tracking position of the rotary head from the back lock position.