JPH0315272B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape stop position detection device for a magnetic recording/playback device.

Generally, magnetic recording and playback device (hereinafter referred to as VTR)
In order to perform tracking adjustment etc.
Four pilot signals with different frequencies are generated in synchronization with the rotation of the rotating magnetic head.
f ₁ , f ₂ , f ₃ , and f ₄ are multiplexed onto a video signal to be recorded in sequence, recorded, and reproduced. In such devices, the magnetic head and pilot signal are connected during playback or when the magnetic tape is stopped.
If it is possible to detect the positional relationship of f ₁ , f ₂ , f ₃ , and f ₄ with the recorded video track, that is, the stop position of the magnetic tape, this can be used to detect the position of the magnetic tape at the time of transition from still image playback to normal playback. It can be used to shorten the pull-in time of travel control servos, maintain pilot signal continuity between previously recorded video tracks and newly recorded video tracks during continuous shooting, and control magnetic tape feed to obtain noiseless still images. performance can be improved.

The relationship between the stop position of the magnetic tape and the level of the pilot signal will be explained below with reference to the drawings.

FIG. 1 shows a video track 2 on a magnetic tape 1.
a, 2b, 2c, 2d, and running trajectories 4a, 4b, 4c of the lower end, upper end, and center of the magnetic heads 3a, 3b (the magnetic head 3b is not shown) when the magnetic tape 1 is stopped. . In the figure, arrows A and B indicate the running direction of the magnetic tape 1 and the running direction of the magnetic heads 3a and 3b, respectively.
T is the track width of video tracks 2a to 2d, W
is the head width of the magnetic heads 3a and 3b, and P is the track pitch in the longitudinal direction of the magnetic tape 1. Further, pilot signals _f1 to _f4 are recorded on each of the video tracks 2a to 2d, multiplexed with the video signal. Note that the video tracks 2a, 2b, 2
Video tracks 2a and 2c and 2b and 2d are recorded using the same magnetic head, respectively. Also, 5a, 5b
is the switching point of the magnetic heads 3a, 3b during reproduction.

Here, the stopping position of the magnetic tape 1 is expressed by the intersection of the running locus 4c at the center of the magnetic heads 3a, 3b and the switching point 5a, and as shown in the figure, the stopping position of the magnetic tape 1 is expressed by the intersection between the center of the video track 2d' and the switching point. 5a is set as 0, and a coordinate x is determined in the opposite direction to the tape running direction A. That is, the stop position of the magnetic tape 1 in FIG. All stop positions can be represented by 4P.

Furthermore, the frequencies of the pilot signals f ₁ to _{f 4} are |f ₁ −f ₂ | |f ₃ −f ₄ |−fa, |f ₁ −f ₄ |||f ₂ −
f ₃ ｜−fb, 100KHz that satisfies the condition fa≠fb
The signal is about 200KHz, and fa and fb are several tens of KH. For example, f ₁ , f ₂ , f ₃ , f ₄ are 102KHz, 118K
Hz, 164KHz, 148KHz, and fa and fb are respectively
16KHz, 46KHz. In addition, the pilot signal f ₁
Since the frequency of ~ _f4 is lower than that of the video signal, the influence of the azimuth effect of the magnetic heads 3a and 3b is small, and reproduction is possible even with magnetic heads having an azimuth different from that during recording.

FIG. 2a shows the playback track widths T ₁ and T ₃ of the video tracks 2a and 2c during one field period at the stop position of the magnetic tape 1 shown in FIG. 1, that is, when x=1.9P. be. here,
The playback track width means the width of the overlapping portion between the magnetic head and the video track. In the figure, the horizontal axis is the time t normalized by one field time tf, where t/tf = 0 and 1 are the times when the centers of the magnetic heads 3a and 3b pass through the switching points 5a and 5b, respectively. Equivalent to. Also,
In the figure, the head width W of the magnetic heads 3a and 3b
is 1.6 times the track width T. Similarly to FIG. 2a, FIG. 2b shows the playback track widths T ₂ and T ₄ of the video tracks 2b and 2a. In the figure, the values of the reproduction track widths T ₂ and T ₄ match at the time of t/tf=0.9, and the magnitude relationship is reversed.

Figure 3 shows the playback track width during one field period with respect to the value of the stop position x of magnetic tape 1.
The size relationship between T ₁ and T ₃ and the reproduction track width T ₁ and T ₃
This shows whether there is a reversal of the magnitude relationship. Here, the area where 0<x<P is X ₁ , the area where P < x < 2P is X ₂ , the area where 2P < x < 3P is X ₃ , and 3P < x < 4P
Let the area be _X4 , furthermore, let the combined area of _X1 and _X3 be _X5 , and the combined area of _X2 and _X4 be _X6 . As is clear from the figure, depending on whether or not there is a reversal in the magnitude relationship of the reproduction track widths T ₁ and T ₃ during one field period, the stop position x of the magnetic tape 1 is
It is possible to determine which of X ₅ and X ₆ is present.

Also, from the same figure, the presence or absence of the above-mentioned reversal, and when there is no reversal, the magnitude relationship of the reproducing track widths T ₁ and T ₃ are used, and when there is reversal, the reproducing track widths T ₁ and T at the time before or after the reversal. By using the magnitude relationship of ₃ , it is possible to determine in which region X ₁ , X ₂ , X ₃ , or X ₄ the stop position x of magnetic tape 1 is located.

The present invention has been made in view of these points,
By utilizing the relationship that the reproduction track width is proportional to the level of the pilot signal included in the reproduction signal of the magnetic head, and the relationship between the magnetic tape stop position and the two reproduction track widths, the stop position of the magnetic tape can be determined. An object of the present invention is to provide a tape stop position detection device for a magnetic recording/playback device, which can detect the tape stop position of a magnetic recording/playback device, thereby improving the performance of a VTR.

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

FIG. 5 is a schematic block diagram of a tape stop position detecting device for a VTR according to a first embodiment of the present invention. In the figure, reference numeral 30 denotes signal level detection means for separately detecting the levels of two pilot signals contained in a reproduced signal reproduced by a reproduction means (not shown);
0, 6 is a balanced modulator, 7a and 7b are bandpass filters whose center frequencies are fa and fb, respectively, 8a,
8b is a wave detector. 9 is a comparator (signal level comparison means) that compares the levels of two input signals and outputs a high potential (hereinafter abbreviated as H) or a low potential (hereinafter abbreviated as L) depending on the magnitude;
40 is a detection signal output means for outputting a signal corresponding to the stop position of the magnetic tape 1, and in the detection signal output means 40, 10 is a pulse that generates a pulse of positive polarity at the rise and fall of an input signal. The generator 11 is a D-flip-flop which operates when the input signal to the trigger terminal T rises and is in the reset state (the output terminal Q is L) when the reset terminal R is H. The generator 12 is an inverting circuit.

FIG. 6 is a timing diagram for explaining the operation of the embodiment shown in FIG. It's on.

Next, the operation will be explained.

First, it is assumed that a stop position detection command is issued at time t= _t0 as shown in FIG. 6a. Before this time, the D-flip-flop 11 is in the reset state, and the output terminal Q, ie, the output O1, is at a low level.

The balanced modulator 6 also includes a rotating magnetic head 3a,
3b and the pilot signal f ₂ are input, but as shown in FIG. 4, the reproduction signal of the rotating magnetic head 3a includes pilot signals f ₁ and f ₃ in addition to the pilot signal f 2 _. ing. Therefore, the balanced modulator 6 to which these signals are input receives beat signals of frequencies fa and fb such that |f ₁ −f ₂ |=fa, |f ₂ −f ₃ |=fb, respectively, as described above. Outputs the included signal. Note that the above reproduction signal is transmitted to the rotating magnetic head 3a,
The signal regenerated by 3b may be amplified and then passed through a filter having the pilot signals f ₁ , f ₂ , f ₃ , and f ₄ within its passband. Then, the band filters 7a and 7b output beat signals fa and fb from the output of the balanced modulator 6 (hereinafter referred to as beat signals fa and fb).
) are separately detected, and the detectors 8a and 8b output respective signal levels as shown in FIG. 6c and d. The outputs of the detectors 8a and 8b are input to a comparator 9 and compared in magnitude. now,
Since the stopping position of the rotating magnetic head 3a is x=2.5P, the detector 8 is detected as shown in FIG. 6c, d, and e.
The outputs of a and 8b have the same value at time t= _t2 , and the output of the comparator 9 is inverted at this time. Furthermore, as in this example, if there is a reversal in the signal levels of the beat signals fa and fb within the field period, the output of the comparator 9 will also be inverted at time t= _t1 , which is the field start point. do.

The signal levels of the beat signals fa and fb are as follows:
This corresponds to the signal level of the pilot signals f ₁ and f ₃ included in the reproduction signals of the magnetic heads 3a and 3b.

Next, the pulse generator 10 generates a pulse of positive polarity in synchronization with the rise and fall of the output of the comparator 9, as shown in FIG.
- Input to trigger terminal T of flip-flop 11. Further, the D-flip-flop 11 has its data terminal D connected to H, and the above-mentioned time t
By inputting a positive pulse to the trigger terminal T at =t ₁ , its output terminal Q becomes H as shown in FIG. 6g.

In addition, FIG. 6b shows the magnetic head switching signal H・Sw.
FIG.

The above explanation is an example in which the output of the comparator 9 is inverted during the field period, but if the stop position x of the magnetic tape 1 is within the area X ₆ shown in FIG. 3, that is, the areas X ₂ and X ₄ , If there is no inversion above,
Since the output of the comparator 9 is fixed at H or L, the output terminal Q of the D-flip-flop 11 remains at L.

Therefore, in the first embodiment shown in FIG. 5, the output after one field period has elapsed since the detection command was issued.
01 allows the magnetic tape stop position x to be detected.
In other words, if output 01 is H, the stop position x is in the area
If output 01 is L at X ₅ (X ₁ or X ₃ ), stop position x
is in the region X ₆ (X ₂ or X ₄ ).

FIG. 7a shows the second embodiment of the present invention, and FIG. 7b shows the outputs 01, 02 and the areas X ₁ , X ₂ ,
This shows the relationship between X ₃ and X ₄ . In the figure, 40' is a detection signal output means, and in the detection signal output means 40', 13 is an exclusive OR circuit, 14 is a pulse generator having the same function as the pulse generator 10 for output 01, and 15 is D- for output 01
A D-flip-flop with the same function as flip-flop 11, 16 is an inverting circuit, 17 and 18 are
19 is an AND circuit and 19 is an OR circuit. Also, the same reference numerals as in FIG. 5 indicate the same parts.

FIG. 8 is a timing diagram for explaining the operation of the second embodiment shown in FIG. 7a, and FIG.
Similar to the explanation of FIG. 6, the case where the stop position of the magnetic tape 1 is x=2.5P is taken as an example.

Next, the operation of this second embodiment will be explained.

In this embodiment, after the stop position detection command is issued at time t= _t0 , the process up to the point where the output 01 becomes H at time t= _t1 is the same as in the case of FIGS. 5 and 6. In this second embodiment, as shown in FIG. 8h and i, the output of the comparator 9 and the magnetic head 3
exclusive OR circuit 1 for switching signals H and Sw of a and 3b
3, and its output is input to the pulse generator 14.
is being entered. Then, the pulse generator 14
As the output of the pulse generator 1 shown in FIG.
From the output of 0, a pulse signal is obtained from which positive polarity pulses synchronized with the rise and fall of the switching signals H and Sw are removed. Such a pulse generator 14
This output triggers the D-flip-flop 15, and the output H of the comparator 9 input to its data terminal D is output to the output terminal Q as shown in FIG. 8J. Note that the D-flip-flop 15 is in a reset state before time t= _t0 . In this way, the D-flip-flops 11, 15
The output terminals Q of are all H, and the AND circuit 1
The output of 7 becomes L due to the output H of the comparator 9 and the output L obtained by inverting the output H of the output terminal Q of the D-flip-flop 11 by the inverting circuit 16.
Furthermore, the output of the AND circuit 18 becomes H by using the H outputs of the D-flip-flops 11 and 15 as two inputs.
The output of the OR circuit 19 becomes H as shown in FIG. 8k. Therefore, as shown in FIG. 7b, the output O1,
Both O2 are H, and the stop position x of magnetic tape 1
It can be detected that is in region _X3 . In addition, the 8th
The timing of the detection command in figure a is different, and the timing t ₁ ,
Even if the order of t ₂ is reversed, it has no effect on the outputs O1 and O2.

In the above explanation, the stop position x of the magnetic tape 1 is x
= 2.5P, that is, in the area X ₃ ,
When the stop position x of the magnetic tape 1 is in the area _X1 , the polarity of the signal shown in Figure 8e is reversed, and D
- L is output to the output terminal Q of the flip-flop 15, and the output O1 shown in FIG. 7b is H and O2 is L.
The state will be as follows. Further, when the stop position x is in the region _X2 or _X4 , as explained in FIGS. 5 and 6, L is output to the output terminal Q of the D-flip-flop 11, that is, the output O1. At this time, the output of the OR circuit 19 is connected to the comparator 9.
The output of is output as is, and the stop position x is the area
Since it is H when it is in the region X ₂ and L when it is in the region X ₄ , the relationship shown in FIG. 7b is obtained.

Therefore, in the second embodiment shown in FIG. 7, the output after one field period has elapsed since the detection command was issued.
From O1 and O2, it is possible to detect which of the regions X ₁ , X ₂ , X ₃ , and X ₄ the stop position x of the magnetic tape 1 is located.

In the first embodiment shown in FIGS. 5 and 6, the signal levels of the pilot signals f ₁ and f ₃ included in the reproduced signals of the magnetic heads 3a and 3b are set to be the same as the pilot signal f ₂ and the beat. Although the same detection is possible by using the pilot signal _f4 instead of the pilot signal _f2 , the same detection is also possible by using a signal with a frequency different from the pilot signals _f2 and _f4 . can also be detected in the same way by appropriately selecting the center frequencies of the band filters 7a and 7b.

Also, the signal levels of pilot signals f ₁ and f ₃ are
It can also be obtained by inputting the reproduced signals to bandpass filters whose center frequencies are f ₁ and f ₃ respectively and detecting their outputs. Furthermore, in this case, it goes without saying that similar detection is possible by using a combination of pilot signals f ₂ and f ₄ instead of pilot signals f ₁ and f ₃ .

As described above, according to the present invention, the reproduction track width and the signal levels of the two pilot signals included in the reproduction signal of the magnetic head are proportional to each other, and the signal levels of the two pilot signals are compared. The magnetic tape stop position can be detected using the relationship between the obtained playback track width and the magnetic tape stop position, which has the effect of improving the performance of the magnetic recording and playback apparatus.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the video track of the magnetic tape and the locus of the magnetic head, Figures 2a and b are diagrams showing the playback track width when playing with the magnetic tape stopped, and Figure 3 is a diagram showing the relationship between the video track of the magnetic tape and the locus of the magnetic head. A diagram showing the magnitude relationship of the playback track width with respect to the stop position of the magnetic tape,
FIG. 4 is a diagram for explaining the operation of the tape stop position detection device for a VTR according to an embodiment of the present invention, and FIG. 5 is a block diagram of the tape stop position detection device for a VTR according to the first embodiment of the present invention. , FIG. 6 is a signal waveform diagram of each part of the device, FIGS. 7a and 7b are a block diagram of the second embodiment of the present invention and a diagram showing the relationship between the output of the device and the tape stop position, and FIG. The figure is a diagram of signal waveforms of various parts in the apparatus of FIG. 7. 3a...Magnetic head (reproduction means), 9...Comparator (signal level comparison means), 30...Signal level detection means, 40, 40'...Detection signal output means. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. Four video tracks of a magnetic tape constitute one cycle, and four pilot signals, first, second, third, and fourth, having different frequencies are transmitted to each of the four video tracks along with a video signal. A tape stop position detecting device for a magnetic recording/reproducing device in which a plurality of rotating magnetic heads sequentially record a tape stop position, the first, third or second, signal level detecting means for separately detecting the levels of the two pilot signals, signal level comparing means for comparing the levels of the two pilot signals, and an output of the signal level comparing means and a switching signal for the rotating magnetic head. and whether or not there is a reversal in the magnitude relationship between the two pilot signals, and if there is no reversal in the magnitude relationship between the two pilot signals, the magnitude relationship between the levels, and detection signal output means for outputting a signal indicating in which of the four areas the magnetic tape stop position is located based on the magnitude relationship of the levels before or after the reversal when the reversal occurs. A tape stop position detection device for a magnetic recording/playback device, characterized in that: