JPH0315273B2 - - 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.
There is a system in which 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 conditions fa≠fb
The signal is about 200KHz, and fa and fb are several tens of KHz. For example, f ₁ , f ₂ , f ₃ , f ₄ are 102KHz,
They are 118KHz, 164KHz, and 148KHz, and fa and fb are 16KHz and 46KHz, respectively. Note that the pilot signals f ₁ to _{f 4} have lower frequencies than the video signal, so
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 2d. 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.
This shows the magnitude relationship between T ₁ and T ₃ . here,
The area where 0<x<P is X ₁ and the area where P < x < 2P is
Let _X2 be the area where 2P<x<3P, and let _X4 be the area _where 3P < x < 4P. As is clear from the figure, the reproduction track widths T ₁ and T ₃ during one field period
If there is no reversal, use the magnitude relationship of the playback track widths T ₁ , T ₃ , and if there is the above reversal, use the playback track widths T ₁ , T 3 before or after the reversal. By using the magnitude relationship of ₃ , the stop position x of the magnetic tape 1 is
It can be determined which of X ₁ , X ₂ , X ₃ , and X ₄ is present.

FIG. 4 shows the relationship between the stop position x of the magnetic tape and the time tx at which the magnitude relationship of the reproduction track widths T ₁ and T ₃ is reversed. Note that tx is the time when the starting point of the field is set to 0. From the same figure, the stop position x of the magnetic tape is either area X ₁ or X _3.
, the value of the stop position x can be detected using the above tx.

The present invention has been made in view of these points,
The stop position of the magnetic tape can be detected by utilizing the relationship that the playback track width is proportional to the level of the pilot signal included in the playback signal of the magnetic head, and the relationship between the stop position of the magnetic tape and the playback track width. and this allows
It is an object of the present invention to provide a tape stop position detection device for a magnetic recording/playback device that can improve the performance of a VTR.

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

FIG. 6 is a schematic block diagram of a tape stop position detection device for a VTR according to an embodiment of the present invention. In the figure, 30 is a 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). , 6 is a balanced modulator, 7a and 7b are bandpass filters whose center frequencies are fa and fb, respectively, and 8a and 8b are detectors. 9 is a comparator (signal level comparison means) 40 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 thereof;
1 is a detection signal output means for outputting a signal corresponding to the stop position of the magnetic tape 1. In the detection signal output means 40, 10, 14, and 20 output pulses of positive polarity at the rise and fall of the input signal. The pulse generators 11, 15, and 21 operate when the input signal to the terminal T rises, and are in the reset state (output terminal Q) when the reset terminal R is H.
is L), D-flip-flop, 12,16
is an inverting circuit, 13 is an exclusive OR circuit, 17,1
8 and 22 are AND circuits, 19 is an OR circuit, 23 is a triangular wave generator that generates a triangular wave in synchronization with the input signal, and 24 is a sample and hold circuit.

FIG. 7 is a timing diagram for explaining the operation of the embodiment shown in FIG. 6, and this is based on an example in which the stop position of the magnetic tape 1 is x=2.5P as shown in FIG. There is.

Next, the operation will be explained.

First, assume that a stop position detection command is issued at time t= _t0 as shown in FIG. 7a. Before this time, each of the D-flip-flops 11, 15, and 21 is in a reset state, and each output terminal Q is at an L 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. _{5, 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 pass beat signals fa and fb at frequencies f ₁ and f ₂ 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. 7c 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.
The outputs of a and 8b have the same value at time t= _t2 , and at this time the output of the comparator 9 is inverted. In addition, 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 start point of the field. 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 positive pulse 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, ie, the output O1, becomes H as shown in FIG. 7g.

On the other hand, as shown in FIG. 7h and i, the output of the comparator 9 and the head switching signal H・Sw for switching the magnetic heads 3a and 3b are input to the exclusive OR circuit 13, and the output thereof is input to the pulse generator 14. Then, a signal is obtained from which the positive polarity pulses synchronized with the rising and falling edges of the head switching signals H and Sw are removed from FIG. 7f. The output of the pulse generator 14 triggers the D flip-flop 15, and the output H of the comparator 9, which is input to the data terminal D, is output to its output terminal Q. As mentioned above, since the output terminal Q of the D-flip-flop 11 is also at H level, the output O2 of the OR circuit 19 is outputted at H level.

Further, as shown in FIG. 7, the pulse generator 20 outputs positive pulses in synchronization with the rising and falling edges of the head switching signal H.Sw, and its output is input to the trigger terminal T of the D-flip-flop 21. Ru. Here, since the data terminal D of the D-flip-flop 21 is connected to its output terminal, the output terminal Q becomes H by the first trigger pulse input after the stop position detection command is issued as shown in Fig. 7m. Then, the following two field periods are considered as one cycle: H,
Repeat L. Further, as shown in FIG. 7o, the triangular wave generator 23 increases the potential from Va at a constant rate of increase (Vb - Va)/tf in synchronization with the rise of the output terminal Q of the D-flip-flop 21. A signal whose potential decreases from Vb to Va is output in synchronization with the fall of the output terminal Q of the D-flip-flop 21. Then, the sample and hold circuit 24 uses the output of the AND circuit 22, which is the logical product of the output of the pulse generator 14 and the output terminal Q of the D-flip-flop 21, as a sampling pulse, as shown in FIGS. The output is sampled and held, and the potential of the output O3 becomes V. Here, the potential V is V- as is clear from the correspondence with FIG.
(Va+Vb)/2.

The above explanation is for the case where the tape stop position x is x=2.5P, but if the tape stop position x is in the area _X3 , the embodiment of FIG.
is H, the output O2 is H, and the potential of the output O3 is Va+(x-
2P)×(Vb−Va)P. As is clear from FIGS. 6 and 7, in this embodiment, regardless of the timing at which the stop position detection command is issued,
After the detection command is issued, the outputs O1 and O2 are set to 1.
After the field time, the above-mentioned stop position information is output for the output O3 after two field times.

Next, if the stop position x is in the _area
The polarity of the signals in figures c, d, and e is reversed,
L is output to the output terminal Q of the D-flip-flop 15. The output O1 is H as in the case of x=2.5P, and the output O2 is L. Also,
The potential of the output O3 is Va+x×(Vb-Va)/P.

Furthermore, if the stop position x is in the area X ₂ or X ₄ , the playback track width is
The magnitude relationship of T ₁ and T ₃ , that is, the beat signals fa and fb
Since the magnitude relationship of the signal levels of D-
The output terminal Q of the flip-flop 11, ie, the output O1, remains at L level. At this time, the output of the comparator 9 is directly outputted to the output O2, which becomes H when x is in the region _X2 and becomes L when it is in the region _X4 . Note that at this time, the potential of the output O3 has no relation to the stop position x.

To summarize the above explanation, in this embodiment, as shown in FIG.
It is possible to detect which of the regions X ₁ , _{X 2} , X ₃ , and _{X 4 the} stop position x is in, and furthermore, if x is in the regions can do.

Note that in the above embodiment, the magnetic head 3
Pilot signal included in the reproduced signals of a and 3b
Although the signal levels of f ₁ and f ₃ are detected by taking the beat with the pilot signal f ₂ , similar detection is possible by using the pilot signal f ₄ instead of the pilot signal f ₂ . signal f ₂ ,
Even if a signal different from f ₄ is used, the bandpass filter 7a,
7b can be similarly detected by appropriately selecting the center frequency. Also, the pilot signal
The signal levels of f ₁ and f ₃ can also be obtained by inputting the reproduction signals of the magnetic heads 3a and 3b to band filters whose center frequencies are f ₁ and f _3, respectively, and detecting their outputs. Furthermore, in the above embodiment,
Although the signal levels of pilot signals f ₁ and f ₃ are compared, it goes without saying that similar detection is possible using pilot signals f ₂ and f ₄ as well.

As described above, according to the present invention, the signal levels of two pilot signals included in the reproduction signal are compared to obtain a comparison output, and the stop position of the magnetic tape is determined by the comparison output and the magnetic head switching signal. , it detects which of the four regions it is in and uses a triangular wave generator to output the distance from one end of each region, so the above-mentioned stopping position can be detected with high precision. It has the effect of improving the performance of the VTR.

[Brief explanation of drawings]

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,
Figure 4 is a diagram showing the relationship when the magnetic tape stop position and the playback track width are reversed in size.
The figures are diagrams for explaining the operation of a VTR tape stop position detection device according to an embodiment of the present invention, FIG. 6 is a block diagram of the device, FIG. 7 is a signal waveform diagram of each part of the device, and FIG. 8 is a diagram showing the relationship between the output of the device and the tape stop position. 3a...Magnetic head (reproduction means), 9...Comparator (signal level comparison means), 30...Signal level detection means, 40...Detected 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 each of the four video tracks has video signals as well as first, second, third, and third video signals having different frequencies.
A tape stop position detecting device for a magnetic recording/reproducing device, wherein four fourth pilot signals are sequentially recorded by a plurality of rotating magnetic heads, the tape stop position detecting device comprising: , signal level detection means for separately detecting the levels of the signals of the third or second and fourth two pilot signals, signal level comparison means for comparing the levels of these two pilot signals, and the output of the comparison means and the above. It has a waveform generator which inputs a head switching signal for switching reproduction signals from a plurality of rotating magnetic heads and whose value increases or decreases in synchronization with the head switching signal, and from the output of the comparing means and the head switching signal,
It detects in which of the areas obtained by equally dividing the one period the magnetic tape is located, and outputs the detection result, and if there is a point in time when the output value of the comparison means is reversed, the point in time is detected. detecting the output value of the waveform generator at and outputting a signal indicating how far the stop position of the magnetic tape is from one end of the area in two predetermined areas of the four areas; What is claimed is: 1. A tape stop position detecting device for a magnetic recording/reproducing device, characterized in that the tape stop position detecting device is provided with a detection signal output means for detecting a magnetic recording/reproducing device.