JPH0344370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 1. The present invention relates to an auto-tracking device in a video tape recorder (hereinafter referred to as VTR) that records and plays back video information signals such as television signals.

VTRs are used in many technical fields because they can extremely easily record and reproduce information signals. In particular, it is well known that it is widely used as consumer video equipment.

By the way, as the demand for high-density recording of information on magnetic tape, which is a recording medium, has increased, the recording track width has been narrowed. There is a limit to the mechanical accuracy of the magnetic tape drive system, magnetic head drive system, etc. Especially for consumer products where cost reduction is required.
In VTRs, narrowing the track width with the above-mentioned mechanical precision is subject to significant restrictions.

In order to achieve high-density recording and reproduction under these constraints, the track width must be narrowed and the magnetic head must be controlled by a tracking servo system during reproduction to ensure that the magnetic head always accurately moves on the track. Scanning requires so-called auto-tracking technology.

Currently, several auto-tracking technologies are known, but they can be broadly classified into the following three types.

(1) One that utilizes the amplitude change of the reproduced RF signal.

(2) A pilot signal is recorded in advance for each track, and leakage signals from adjacent tracks are used.

(3) Those using an auxiliary head.

Each of the above methods controls the position of the magnetic head and the feeding speed of the tape based on the detected tracking error signal.If the track width is narrowed to, for example, 10 μm or less, these methods can be used independently. It is not possible to obtain a sufficient tracking error signal just by using this method.

The present invention employs the advantages of methods (2) and (3) above to provide an auto-tracking device for a VTR that can perform good tracking even for a VTR with a narrow track width. purpose.

In order to achieve the above object, the present invention uses a main signal recording head in which a recording head for a main signal (video signal) and a head for reproducing the main signal are separate, and the mounting position of the head is devised. A pilot signal is recorded and reproduced using the main signal, and the relative position of the reproduction head and the track is controlled using the pilot signal so that the main signal reproduction head always accurately scans the track.

Next, the present invention will be specifically explained with reference to illustrated embodiments.

Figure 1 shows the present invention in a two-head helical scan.
This is a diagram for explaining the rotary head unit in an embodiment applied to a VTR. 1W and 2W are rotary heads for recording main signals, respectively, and as shown in the figure,
They are mounted so that they rotate at the same position on the same rotational plane with an angular spacing of 180° from each other. 1R and 2R are main signal reproducing heads, recording head 1
Like W and 2W, they are mounted so that they rotate at the same position on the same rotational surface with an angular interval of 180 degrees from each other.

In addition, as shown in FIG. 2, the recording head 1
The void length gw of the void 1WG (2WG) in W (2W),
Gap 1RG (2RG) of playback head 1R (2R)
The void length g _R of is set as g _W >g _R , and the centers are arranged so that their center lines coincide. In the illustrated embodiment, g _W =2g _R.

In FIG. 1, the magnetic tape 3 is connected to the guide drum 4.
However, it is wrapped diagonally over its 180° corner range. This magnetic tape is run in the direction shown by the arrow 5 in the figure, and the head 1W,
Recording and reproduction are performed by rotating 1R, 2W, and 2R in the direction shown by arrow 6.

Figure 3a shows the recording pattern recorded as described above, with heads 1W and 2W recording tracks 1A and 1.
Recording tracks such as B, 2A, 2B, 3A, 3B, . . . are formed. When recording the main signal for each track, pilot signals of four different frequencies are sequentially recorded for each track.

Track A recorded with a 1W head has a frequency of
The recording frequency is determined for each track, such as a pilot signal of frequency f ₁ or f ₃ , and a pilot signal of frequency f ₂ or f ₄ for track B, which is recorded by head 2W.

During playback, this pilot signal is played back by the recording head, and heads 1W and 2W
The pilot signals reproduced are the pilot signal of the track being scanned and the pilot signals of the tracks on both sides adjacent to that track.

Therefore, let the horizontal frequency be f _h , f ₁ = 10.5f _h , f ₂ =
If 9.5f _h , f ₃ =6.5f _h and f ₄ =7.5f _h are selected, the following relationship is established between the pilot signals reproduced by heads 1W and 2W during reproduction.

｜f ₂ −f ₁ ｜=｜f ₄ −f ₃ ｜=f _h ｜f ₂ −f ₃ ｜=｜f ₄ −f ₁ ｜=3f _h In other words, the reproduction pilot signal is If a signal component is frequency-converted, the frequency-converted output will be of two types: f _h component and 3f _h component.

That is, when playing back track A, if the head shifts upward in FIG. 3, the f _h component increases, and conversely, if the head shifts downward, the 3f _h component increases. Furthermore, when reproducing track B, when the head shifts upward, the 3f _h component increases, and when the head shifts downward, the f _h component increases. This relationship is shown in Figure 3b.

Therefore, the f _h component and the 3f _h component can be extracted using a bandpass filter and used as a tracking error signal. This tracking error signal causes the main signal reproducing head 1 to
As R and 2R scan on a predetermined track,
It becomes possible to perform auto tracking.

Next, a description will be given of a device for moving the heads 1R and 2R so that they are correctly positioned on the track in order to perform the above-mentioned auto-tracking.

FIG. 4 shows an embodiment of an autotracking device according to the present invention, in which a recording head 1W (2W) and a reproducing head 1R (2R) are attached in the longitudinal direction of a bimorph plate 7, which is an electro-mechanical transducer. .
In this case, head 1W (2W) and head 1R (2W)
The width direction of the gap R) is the surface 7 _S of the bimorph plate 7.
The two heads are installed so that they are perpendicular to each other and the gaps between the two heads are arranged in the relationship shown in FIG. The other longitudinal end of the bimorph plate 7 to which the head 1W (2W) and the head 1R (2R) are not attached is fixed to a base plate 11 of a rotating head cylinder (not shown). By applying a voltage to the bimorph plate 7 having the above structure through the input terminals 8A, 8B, and 8C, the bimorph plate 7 is displaced in a direction perpendicular to its surface _7S , and the head 1W (2W) is displaced.
And the head 1R (2R) can move in the width direction of the gap.

Note that the terminals 9A and 9B are used as main signal reproduction terminals, and the terminals 10A and 10B are used as main signal and pilot signal recording terminals, and pilot signal reproduction terminals.

Here, the mounting positions of the main signal recording head 1W (2W) and the main signal reproducing head 1R (2R) should be aligned, especially the center line of the gap length of both heads, as explained in Fig. 2. The reason for installing it will be explained below.

For example, as shown in Figure 5, the void length
g _W ' main signal recording head 1W'(2W') and gap length
When installing head 1R'(2R') for main signal reproduction of g _R ', in other words, one end of the gap between both heads in the width direction should be offset from each other by a certain value (1/2g _R ' in Figure 5). Consider the case. (Here, g _W ′
= g _R ′).

In this case, as shown in FIG. 6a, pilot signals of two different frequencies f ₁ ' and f ₂ ' are recorded at track pitch g _W ' (g _R ') for each track.
During playback, the main signal recording head 1W'(2W')
This will scan the boundaries of the track. When the main signal reproducing head 1R' is reproducing track B and the head shifts upward and scans,
When the f ₁ ′ component increases and shifts downward, the f ₂ ′ component increases.

Conversely, in track A, when the head shifts upward, the f ₂ ' component increases, and when the head shifts downward, the f ₁ ' component increases (FIG. 6b). In this way, a tracking error signal corresponding to the tracking deviation can be obtained, and the head can be moved to perform auto-tracking.

However, this method has the following drawbacks.

(1) The track width recorded on the tape does not become a constant track width due to the difference in the mounting positions of the main signal recording heads 1W' and 2W', and vibrations during tape running. For example, as shown in FIG. 7, if the width T ₂ of one track is different from the width T ₁ of another track (T ₁ >T ₂ ),
The head scans the positions indicated by R' and 1W', and the reproducing head 1R' no longer scans the center of the track.

(2) Adjacent tracks 1A and 1B, 2A and 2B,...
Since the pilot signals are recorded at different heads of 1W' and 2W', delicate adjustments are required to record them at the same level.

If this adjustment is not done well, there will be a difference in tracking accuracy during playback.

(3) When heads 1R' and 1W' scan as shown in Figure 8, the pilot signal of track 2B
f ₂ 'component and track 3B pilot signal
The sum of the f ₂ ' components is in equilibrium with the pilot signal f ₁ ' component of track 3A, resulting in a mistracking state.

The above-mentioned drawbacks do not occur in the structure of the present invention in which the rotary head for recording the main signal and the head for reproducing the main signal are attached so that the center lines of the gap lengths of the two heads coincide with each other.

Next, a circuit for recording and reproducing a pilot signal on a track and controlling a head according to the present invention will be explained with reference to FIG.

In FIG. 9, 11 is an input terminal for a horizontal synchronizing signal, 12a, 12b, 12c, and 12d are respectively generating pilot signals f ₁ , f ₂ , f ₃ , and f _4. Oscillator 13 is a 30Hz head switching signal SW30. The input terminal 14 of is a ring counter with a 4 count period,
15a, 15b, 15c, and 15d are analog switches; 16 is a recording video processing circuit that processes video signals to record them on a magnetic tape; 17 is an input terminal for a reproduced RF signal reproduced from the magnetic tape;
8a, 18b, 18c, and 18d are bandpass filters 1 and 1 for extracting pilot signals, respectively.
9 is an adder, 20 is an envelope detection circuit, 21
is a comparator, 22 is a head switching signal SW30
Delayed pulse circuit that generates more delayed pulses, 2
3 is an AND gate, 24 is a frequency conversion circuit, 25
e, 25f are band pass filters 26e, 26f
is an envelope detection circuit, 27 is a differential amplifier, 2
8e and 28f are analog switches, 29 is a low-pass filter, 30 is a servo characteristic compensation circuit, 31,
32 is a bimorph plate to which magnetic heads 1R, 1W, 2R, and 2W are attached.

The operation of the circuit shown in FIG. 9 will be described below with reference to the timing chart shown in FIG. 10.

A horizontal synchronizing signal taken out from a color signal circuit of a VTR video signal system is input to a horizontal synchronizing signal input terminal 11. Pilot signals f ₁ , f ₂ , f ₃ , f ₄ which are phase-locked using this as a reference phase are generated by pilot signal generators 12a, 12b, 12c, and 12d.
Generate each. These pilot signals are generated all the time, and the analog switches 15a, 1
5b, 15c, and 15d, the ring counter 14 sequentially switches the head switching signal SW30 by frequency-dividing four-phase pulses φ ₁ , φ ₂ , φ ₃ , and φ ₄ , and generates a pilot signal for each successive track on the magnetic tape.
f ₁ , f ₂ , f ₃ , and f ₄ are recorded together with the main signal from the recording video signal processing circuit 16.

As shown in FIG. 11, the ring counter 14 that frequency-divides the head switching signal SW30 includes an inverter 33, a flip-flop 34, and an AND gate 3.
5, 37 and NOR gates 36, 38, and is connected to the set terminal 39 of the flip-flop.
By inputting a set pulse from _{the AND gate 23, four-phase pilot signals f 1 ,} f ₂ ,
Generates f ₃ and f ₄ .

This pilot signal is mixed with the recorded video signal (main signal) from the recorded video signal processing circuit 16 and recorded on the magnetic tape 3 (FIG. 1) by the main signal recording head 1W (2W).

Next, the operation during playback will be explained.

RF reproduced with main signal recording head 1W (2W)
The signal is input to the reproduction RF input terminal 17. Pilot signals f ₁ , f ₂ , included in the regenerative RF input
f ₃ and f ₄ are respectively bandpass filters 18
a, 18b, 18c, and 18d and added to adder 19. On the other hand, the pilot signal f ₁ from the bandpass filter 18a is applied to an envelope detection circuit 20, envelope-detected, and compared with an appropriate level E in a comparator 21, and the field (track) in which the pilot signal f ₁ is recorded is detected. determine something.

That is, as shown in the time chart of FIG. 12, by inputting the pulse obtained by delaying the head switching signal SW30 in the delayed pulse circuit 22 and the output of the envelope detection circuit 20 to the AND gate 23,
Determine the recorded track of the pilot signal _f1 .

Therefore, the phase of the four-phase pulses from the ring counter 14 is set to _φ1 every time the pilot signal of frequency _f1 is reproduced. In other words,
A signal always having the same frequency as the pilot signal of the reproduction track is sent to the frequency conversion circuit 24 as a local signal.
join. The frequency-converted signal is separated into a frequency component of f _h and a frequency component of 3f _h by bandpass filters 25e and 25f, which are detected by envelope detection circuits 26e and 26f, respectively, and then sent to a non-inverting differential amplifier 27. Applied to input and inverting input.

The differential amplifier 27 outputs a signal corresponding to the track deviation, but as explained above, the polarity of the signal is reversed depending on the track depending on the direction of the deviation. Therefore, when the track A is on, the non-inverted output of the differential amplifier 27 is passed through, and when the track B is on, the inverted output is passed through, so that these are switched by the analog switches 28e and 28f to align the polarities. The signals with the same polarity are passed through the low pass filter 29.
By passing it through, a stable tracking error signal is obtained, and the servo characteristics are further improved by the servo characteristics compensation circuit 30. The tracking error signal obtained in this way is
bimorph board 31 with magnetic head 2W installed.
By adding 2R and 2R to the bimorph board 32, tracking is corrected and auto-tracking is performed.

As explained above, the VTR autotracking device of the present invention has a rotary head for recording the main signal and a rotary head for reproducing the main signal on an electro-mechanical transducer that can be displaced in a direction perpendicular to the recording track. ,
The center lines of the gaps in the width direction are arranged in close proximity to each other, and during recording, the main signal and the pilot signal are recorded by the rotary head for recording, and during reproduction, the rotary head for recording the main signal records the pilot signal. The scanning position of the rotary head for main signal reproduction relative to the track is controlled by the reproduced output of this pilot signal, so that even in VTRs with narrower tracks, the magnetic head is always on top of the track. can be scanned accurately,
Very high quality video reproduction without crosstalk from adjacent tracks can be performed.

Further, according to the present invention, since the recording head and the reproducing head are separate, it is possible to use the most suitable magnetic head for recording and reproducing. That is,
The recording head has a wide gap length and can sufficiently record low frequency components, and the playback head has a narrow gap length and can reproduce high frequency components with high sensitivity. You can improve your performance.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of a rotary head device of a VTR to which the present invention is applied, FIG. 2 is a layout diagram of a magnetic head in an embodiment of the present invention, and FIGS. 3 a and b
4 is a plan view of a recording pattern on a magnetic tape recorded according to an embodiment of the present invention, and an explanatory diagram showing changes in reproduction output with respect to track deviation. FIG. 4 shows a state in which a magnetic head is attached for auto-tracking. In order to explain the effect of the magnetic head arrangement of the present invention, the schematic diagram in FIG.
b is a plan view of the recording pattern according to the magnetic head arrangement shown in FIG. 5, and an explanatory diagram showing changes in reproduction output with respect to track deviation; FIGS. 7 and 8 are plan views of the recording pattern; FIG. A circuit diagram for controlling recording and reproduction of pilot signals and auto-tracking in an embodiment of the invention, FIG. 10 is a timing chart of the ring counter in FIG. 9, and FIG. 11 is a configuration of the ring counter in FIG. 9. 12 are timing charts illustrating the operation of the circuit shown in FIG. 9 during reproduction. 1W, 2W...Magnetic head for recording, 1R, 2R...
Reproducing magnetic head, 7... Bimorph board, 11... Horizontal synchronizing signal input terminal, 12... Pilot signal oscillator, 14... Ring counter, 16... Recorded video signal processing circuit, 17... Reproducing RF input terminal, 20... Envelope detection circuit, 21...Comparator, 24...
Frequency conversion circuit, 27...differential amplifier, 30...servo characteristic compensation circuit.

Claims (1)

[Claims] 1. Two video signal recording magnetic heads that rotate at the same position on the same rotational surface at an angular interval of 180° from each other, and two magnetic heads for recording video signals that are arranged close to each of the recording magnetic heads and rotate at the same position on the same rotational surface at an angular interval of 180° from each other. In an auto-tracking device for a VTR having two video signal reproducing magnetic heads rotating at the same position, each pair of the recording magnetic head and reproducing magnetic head arranged close to each other has a gap between them. The recording track is mounted on an electro-mechanical transducer element that can be displaced in the vertical direction of the recording track so that the center lines in the width direction coincide with each other. The recording magnetic head reproduces the pilot signal, and a tracking error signal extracted from the reproduced pilot signal is applied to the electro-mechanical conversion element to control the scanning position of the reproduction magnetic head. Featured VTR
auto tracking device.