JPS59201259A - Method for detecting stop position of magnetic tape - Google Patents

Abstract

PURPOSE:To detect a tape stop position with high precision by outputting which area the tape stop position is in or how far the stop position is from one terminal of the area by the level comparison output between two pilot signals and the switching signal of a magnetic head. CONSTITUTION:A signal level detecting circuit 30 detects separately the levels of two pilot signals in a reproducing signal reproduced by a reproducing means. A comparator 9 compares the levels of the two input signals with each other to output a high-level or low-level signal according to the comparison result. A detection signal output circuit 40 outputs a signal which indicates which of areas obtained by dividing one period equally into four by track pitch the stop position of the magnetic tape is in on the basis of the comparison output and the switching signal of the magnetic head, and also outputs a detection signal which indicates how far the stop position is from one terminal of two specific areas among the four areas.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting the stop position of a magnetic tape, and particularly to a method for detecting the stop position of a magnetic tape during playback and stop of a magnetic tape in a magnetic recording and playback device that records and plays back using a rotating head, such as a video tape recorder. This invention relates to a detection method for detecting a position.

In a video tape recorder (hereinafter referred to as VTR), the magnetic head and video trunk are aligned (track alignment) during playback.
In order to A travel control servo system is provided. However, conventionally, when the magnetic tape is stopped, the relative relationship between the tape stop position and the magnetic head position is unclear, so when the magnetic tape starts running from a stopped state, The 1-ranking cannot be obtained until after the pilot signal is detected, and therefore the pull-in time of the servo system is long. Also, in VTR,
If continuous shooting is performed, the pitch of the magnetic tape pattern may be disturbed at the continuous portion, and the continuity of the pilot signal may be lost. However, in these cases, if the stop position of the magnetic tape relative to the rotating head is detected when the magnetic tape is stopped, then when the detection signal is used to move to the next running state, the pull-in time of the servo system can be adjusted. It would be possible to shorten the time and maintain the continuity of the pilot signal for continuous shooting.

Therefore, a main object of the present invention is to provide a magnetic tape stop position detection method that can detect the stop position of a magnetic tape in a stopped state.

To summarize this invention, the first . The levels of the third or second and fourth pilot signals are detected separately, and the stop position of the magnetic tape is determined based on the result of comparing the levels of these two pilot signals and the switching signal of the magnetic head. Outputs a signal indicating in which region one period is divided into four by the track pitch, and in two predetermined regions among the four regions, the stop position of the magnetic tape is at one end of that region. It is designed to output a detection signal indicating how far away the object is.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

FIG. 1 is a diagram schematically showing the positional relationship between a magnetic tape and a magnetic head.

First, the relationship between the video track on the magnetic tape surface and the traveling locus of the magnetic head will be explained with reference to FIG. Video tracks 2a, 2b, 2c, 2d on magnetic tape 1 and magnetic head 3a when magnetic tape 1 is stopped
(The magnetic head 3b is not shown). The magnetic tape 1 has a magnetic head 3a in the direction shown by arrow A.

The magnetic head 3b is assumed to run in the direction shown by arrow B, and the track width of the video tracks 2a to 2d is
The head width of a and 3b is w, and the track pitch in the longitudinal direction of the in magnetic tape is P. Magnetic heads 3a, 3b
The traveling locus is the traveling locus 4a of the lower end, upper end, and center of the magnetic heads 3a, 3b.

4b, 40. In addition, pilot signals f1 to r4 are sequentially recorded on each video track 2a to 2d, multiplexed with the video signal, and video tracks 2a and 2G and video tracks 1 to 2b and 2dt are multiplexed with the video signal.
These two magnetic heads (those with different azimuths are used. Switching points 5a and 5b are respectively set.

The stopping position of the magnetic tape 1 is expressed by the intersection of the central traveling locus 4C of the magnetic heads 3a, 3b and the switching point 5a, and now the X coordinate of the magnetic tape 1 is set in the 5-hand direction, and the zero point is the center of the video track 2d. It is assumed that the traveling locus 4G intersects with the switching octopus India 5a. The stopping position of the magnetic tape 1 shown in FIG. 1 is at x-1,911.

Video tracks 2a to 2d are pilot signals fI to f4
is recorded periodically with 4 tracks as one period, so by using the pitch p, x=O~4p
can represent all stopping positions.

The pilot signals f1 to f4 are signals each having a different constant frequency in a frequency range lower than that of the low-frequency conversion color signal, and there is B between the mutual frequencies.

fz l#lfs f< 1=fA, lr, f<
1#lf2 f-1-fa, a signal of about 100 kHz to 200 kHz that satisfies the condition fA≠[8. For example, f, , T2. 102 kHz in the order of f, j,
z, 118 kHz, 164 kHz, and 148 kHz have been proposed. Also, the frequency difference rf is several tens of kilohertz
2 (in the above example 16 kl-12, 4
6kH2). The pilot signal f, ~
Since f4 has a lower frequency than the video signal, the influence of the azimuth effect of the magnetic heads 3a and 3b is small, and reproduction is possible even with a magnetic head with an azimuth different from that during recording.

Regarding the stop magnetic tape 1 as described above, FIG.
) is the stop position of the magnetic tape 1, that is, X=1.911
In this state, the playback track width T+ of the video tracks 2a, 2b that the magnetic heads 3a, 3b trace during one field period
, T-.

Here, the playback track width means the width of the overlapping portion between the magnetic head and the video rack. In the figure, the horizontal axis is the time t normalized by one field time t↑, and t/1f-0 and 1 are the magnetic heads 3a and 3, respectively.
The center of the head of b is the switching point 5a, 5b.
corresponds to the time it takes to pass through Also, in the same figure, the head ends W of the magnetic heads 3a and 3b are located at 1.0 mm below the track width.
Designed to be 6 times larger. FIG. 2(b) shows the video track 2b at the same magnetic tape stop position as in FIG. 2(a).

2d shows the reproduction track width T2, T. In the figure, the values of the reproduced track widths T2 and T4 match at time points t/l-H-0 and 9, and the magnitude relationship is reversed. As can be seen from the example shown in FIGS. 2(a) and 2(b), depending on the magnetic tape stop position, the relationship between the two playback i~rack widths T, , T8 and the widths 2 and 4 has a unique size relationship. have

Figure 3 shows the magnitude relationship of the reproduction track widths T, , T, and T2°T4 in one field period with respect to the stop position X of the magnetic tape based on the above definition. be. Here, the area of O〈X
, the region where p≦x≦2p is X2.20<X, and the region where <3p is X3.311≦x≦4p is X. As is clear from the figure, the playback track width T1 and the width of the track during one field period.

And in comparing the two sets of T2 and T4, X, ~X
In any of the regions 4, there is a set in which the magnitude relationship of the playback track width of one set is not reversed, and by knowing the magnitude of the playback track width in this set that is not reversed, the stop position x of the magnetic tape can be determined in the regions X+, X2 , X-, or X4 can be determined. For example, playback i~rack I! l In comparing T, and T, if the king is always 18 or more, the stop position of the magnetic tape × is the area MX2
If the IC is always T1 or less, then the stop position x is in the area X4. Alternatively, it is also possible to determine in which region of X or -X4 the stop position @X of the magnetic tape 1 is located by knowing the magnitude relationship of the reproduction track width and the presence or absence of a point at which the magnitude relationship is reversed.

However, in FIG. 3, in area x 2, (X =
D , t −j4 ) and (x = 2p , t
-0), the playback track width is T,
-T8, (X = p, t = O) and (X
When =211°1=1(), the playback track width is T2-th. Also in the area x 4 (X = 3p,'
When t - [dry] and (X = 4p, t = O), the playback track width becomes T, =T, and (X = 3p,
t = 0) and (x = 4r+, t = t+), the playback 1 to rack width becomes T z "' T-.

Here, pilot signals r, , T2. Since t, , r, are written superimposed on the video track, the reproduction track width T, , T2, T3, T< is the pilot signal f included in the reproduction signal of the magnetic heads 3a, 3b.
It has a proportional relationship with the amplitudes of +-, fz, and ra tf4, respectively.

This invention is based on the proportional relationship between the reproduced track width and the amplitude of the pilot signal as shown in FIG.

The stop position @X of the magnetic tape 1 and the playback track width T7 as explained using FIGS. 2 and 3. T2, T8. T4
The position of the magnetic tape is detected using the correspondence relationship with the magnetic tape.

FIG. 4 shows the relationship between the stop position X of the magnetic tape and the playback trunk width T7, or the time point CA when the magnitude relationship between T2 and T4 is reversed.

In addition,. is the time when the starting point of the field is O. What this figure 4 means is that within each region X to X4, 1, /1 differs depending on the stop position, and in any of the regions This means that the relationships are expressed in equal proportions. Therefore, if the same reference voltage is generated in each region as shown in Figure 4 and one reference voltage value is extracted, the position within the region can be determined from the extracted voltage value. can. In this way, it is possible to know not only whether the magnetic tape is in area x1 or x4, but also the position within that area, which makes it possible to know the exact stop position of the magnetic tape, which is even more effective.

FIG. 5 is a schematic block diagram of a tape stop position detection device for a VTR to which the present invention is applied. In FIG. 5, a signal level detection circuit 30 separates and detects the levels of two pilot signals contained in a reproduced signal reproduced by a reproduction means (not shown). This signal level detection circuit 30 includes a balanced modulator 6, a bandpass filter whose center frequency is fA + fB, and a detector f.
3a.

8b. The comparator 9 compares the levels of two input signals and outputs a high level or low level signal depending on the magnitude.

The detection signal output circuit 40 outputs a signal corresponding to the stop position of the magnetic tape 1. This detection signal output circuit 40 includes pulse generators 10, 14, and 20 that generate positive polarity pulses at the rise and fall of the input signal. The detection signal output circuit 40 is a D-type flip-flop that operates when the input signal to the trigger terminal T rises and enters the reset state (output terminal Q becomes low level) when the reset terminal R is high level. 11.15'' and 21. Roughly speaking, the detection signal output circuit 40 includes an inverter 12.16, an exclusive OR circuit 13, AND circuits 17, 18 and 22, and an OR circuit 19 synchronized with the input signal. The sample and hold circuit 24 includes a triangular wave generator 23 that generates a triangular wave.

FIG. 6 is a timing diagram for explaining the operation of the tape stop position detection device shown in FIG. ing.

Next, the operation will be explained with reference to the fifth factor and FIG. 6. First, as shown in FIG. 6(a), time t=to
Suppose that a stop position detection command is issued. Before this time, each of the D-type flip-flops 11, 15 and 21 is in the state 1~? When it is cold, each output terminal Q is at a low level. In addition, the balanced modulator 6 is supplied with reproduction signals of the rotating magnetic heads 3a and 3b and a pilot signal [2].
However, in the reproduction signal of the rotating magnetic head 3a, in addition to the pilot signal [2, the pilot signal f
, ,f, are included. Therefore, the balanced modulator 6 to which these signals are input is lf+
r21=fA, ll'2 fa 1=f8, the frequencies are fA and f[! Outputs a signal containing the beat signal. Note that the above-mentioned reproduction signal is transmitted to the rotating magnetic head 3a.
, 3b, and then the pilot signal @f 7. It may be passed through a filter having h, f-, and f4 in the passband. Then, the bandpass filters 7a and 7b select the frequency f from the output of the balanced modulator 6.
, , ra beat signals are detected, and the detectors 8a and 8b
is shown in Figure 6(C).

A signal with a level as shown in (d) is output. The outputs of the detectors 8a and 8b are input to a comparator 9 and their levels are compared.

Now, since the stopping position of the rotating magnetic t\rad a is X = 2.5P, Fig. 6 (c), (d), (e
), the outputs of the detectors 8a and 8b are at time t.
-12, the same value is obtained, and at this point the output of the comparator 9 is inverted. In addition, as shown in this example, if there is a reversal of the signal levels of the Be 1 signals fA and fB within the field period, the comparator will be 9
The output of is inverted.

The signal levels of J, beat signals gfA, f, etc. match the signal levels of the pilot signals f, , f8 included in the reproduced signals of the magnetic t\rad a, 3b.

Next, as shown in FIG. 6(f), the pulse generator 10 generates a positive pulse in synchronization with the rise and fall of the output of the comparator 9, and this pulse is transmitted to the D-type flip-flop 11. input below the trigger terminal. Also,
The data terminal of the D-type flip-flop 1 is set to a high level, and due to the input of the positive pulse to the trigger terminal T at the above-mentioned time t-i, the output terminal Q1, that is, the output 01, is set to the high level. The level becomes high as shown in Figure 6 (0).

On the other hand, as shown in FIG. 6(h) and (+), the output of the comparator 9 and the head switching signal 1.8w for switching the magnetic heads 3a and 3b (17) are input to the exclusive OR circuit 13, and When the output is input to the pulse generator 14,
As shown in FIG. 6 <r>, a signal is obtained in which positive polarity pulses synchronized with the rising and falling edges of the head switching signals H and Sw are removed.

The D-type flip-flop 15 is triggered by the output of the pulse generator 14, and the high level signal of the output of the comparator 9 inputted to the data terminal is outputted to its output terminal Q. As described above, since the output terminal Q of the D-type flip-flop 11 is also at a high level, a high level signal is outputted to the output 02 of the OR circuit 19.

Further, as shown in FIG. 6, the pulse generator 20 is
A positive pulse is output in synchronization with the rise and fall of the head switching signals H and SW, and the output is inputted to the bottom of the terminal of the D-type flip 70 and the knob 21. Here, D
Since the data terminal of the type flip-flop 21 is connected to its output terminal 0, the output terminal Q is as shown in FIG.
As shown in Figure 2, after the stop position detection command is issued, the first trigger pulse is input and becomes high level.
High level and low level are repeated with each field period as one cycle. In addition, the triangular wave generator 23 is shown in FIG. 6 (0).
As shown in , the output terminal Q of the D-type flip-flop 21
The potential increases from Va at a constant rate of increase (V
It outputs a signal whose potential increases from vb to Va) and decreases from vb to Va in synchronization with the fall of the output terminal Q of the D-type flip-flop 21. As shown in FIGS. 6(U-) to 6(p), the sample and hold circuit 24 includes an AND circuit 22 which is a logical product of the output of the pulse generator 14 and the output terminal Q of the D-type flip-flop 21.
The output of the triangular wave generator 23 is sampled and held using the output of the triangular wave generator 23 as a sampling pulse, and the potential of the output 03 becomes ■. Here, the potential ■ is V-<Va +Vb)/2.

The above explanation is for the case where the tape stop position x1fix=2.5P, but the tape stop position X is the area X.

5, the embodiment of FIG.
l -Va n/P. As is clear from FIGS. 5 and 6, regardless of the timing at which the stop position detection command is issued, after the detection command is issued, the output is 0. , o2
For output 03, the above-mentioned stop position/amount information is output after one field time has elapsed, and for output 03, after two field time has elapsed.

Next, if the stop position
The polarities of the signals c), <6), and <e) are inverted, and a low level signal is output to the output terminal Q of the D-type flip-flop 15. For output 0, the above-mentioned ×-2,5P
A high level signal is output in the same way as in the case of , and the output 02 becomes low level. Also, the potential of the output O8 is Va
+XX(Vb-Va)/P.

Roughly speaking, when the stop position x is in the area X2 or X, the playback track width T, ,T, as shown in FIG.
Since the magnitude relationship between the signal levels of the beat signals fA and f8 is not reversed, the output terminal Q1 of the D-type frimbflop 11, that is, the output 0. remains at low level. At this time, the output of the comparator 9 is directly outputted to the output 02, which becomes a high level when X is in the area '4 x 2, and becomes a low level when it is in the area x4. Incidentally, the potential of the output O3 at this time has no relation to the stop position X or the like.

To summarize the above explanation, in this invention, as shown in FIG. ．． Depending on the high level and low level of 02, the stop position × is region XX.

It can detect whether it is in X2, X3, or X4, and if roughly
The value of x can be detected from the Q position of .

Note that in the above description, the magnetic head 3a is referred to as the magnetic head 3a.

The signal level of the pilot signal "1.r" included in the reproduced signal of 3b is detected by taking the beat with the signal r2 from pylon 1, but the same result can be obtained by using the pilot signal 8f4 instead of the pilot signal "2". Furthermore, even if a signal different from the pilot signals f2, f is used, the center frequency of the bandpass filters 7a, 7b can be set to 5'f4.
Detection can be made in the same manner by selecting the appropriate selection. Furthermore, the signal level of the pilot signal f+43 is determined by the magnetic head 3a.

The center frequencies of the reproduced signals of 3b are f, , f, respectively.

It can also be obtained by inputting it to a bandpass filter and detecting its output. Furthermore, in the above explanation, J5 compares the signal levels of pilot signals r and f, but it goes without saying that similar detection is possible using pilot signals t2 and r4. .

As described above, according to the present invention, a comparison output is obtained by comparing the signal levels of two pilot signals included in the reproduced signal, and the comparison output and the switching signal of the magnetic head are used to control the magnetic tape. Since the system detects which of the four regions the stop position of the vehicle is located in and outputs the distance from one end of each region, the stop position can be detected with high accuracy. Therefore, as explained at the beginning, if this invention is used, it is possible to shorten the pull-in time of the magnetic tape running control servo system, maintain the continuity of the pilot signal for continuous shooting, and obtain other noiseless still images. This is effective for magnetic tape feed control, etc.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the video track of the magnetic tape and the locus of the magnetic head. FIG. 2 is a diagram showing the reproduction track width when reproduction is performed with the magnetic tape stopped. FIG. 3 is a diagram that does not show the magnitude relationship of the reproduction track width with respect to the nine stop positions of the magnetic tape. FIG. 11 is a diagram showing the relationship between the stopping position of the reference tape and the point in time when the magnitude (i) of the reproduction track width is reversed. FIG. 5 is a block diagram of a Dave stop position detecting device to which this invention is applied. FIG. 6 is a signal @ waveform diagram of each part of the one-table stop position detection Vi lamp shown in FIG. FIG. 7 is a diagram showing the relationship between the output of the tape stop position detection device shown in FIG. 5 and the tape stop position. 65 in the figure, 3a is a magnetic head, 6 is a balanced modulator, 7
a, (b is the band j practice filter, P, a, 8b fJu
'A wave generator, 9 is a comparator, 10, 14.20 is a pulse generator, 11.15.21 is a D type flip-flop,
30 is a signal level detection circuit, 40 is a detection signal output circuit,
23 is a triangular wave generator, and 24 is a thimble hold circuit. Figure 1 Figure 2 Figure 2 (α) (b) Figure 83 Figure 4 Figure 4 p, --- ''/ll Figure 5 Figure 7 Figure 11' Display of the Chief Minister Patent application No. 58-76711 2, Title of the invention: A company that makes a method for detecting the stop position of a magnetic tape Representative: Hitoshi Katayama Department 5, Claims column and Detailed description of the invention column 6 of the specification to be amended; Contents of the amendment (1) The claims of the specification are as shown in the attached sheet. (2) "T/lf=" in page 8, line 4 of 11t3
o. '1' is corrected to 'j, /lF = Q, 1j. (3) Specification box page 11, line 7, line 9 to line '10
Correct the line rtx,'tJ to rH:,-'t4. 2, Claim (1) The four video tracks of the magnetic tape constitute one cycle, and each of the four video tracks 1 to 1 rack has a video signal as well as the 1st to 1st tracks of different frequencies. 2nd ° 3rd and 4th 4th
In a magnetic recording and reproducing apparatus that sequentially records pilot signals of h< the first . Third or second. A stop position of the magnetic tape tracks the one period based on a connecting beam and a magnetic head switching signal, which are obtained by separately detecting the levels of the fourth two pilot signals and comparing the levels of the two pilot signals. It outputs a signal indicating which of the four areas divided by the picker is located, and in two predetermined areas among the four areas, the magnetic tape's y stop position is within the area. A method for detecting a stop position of a magnetic tape, characterized in that a detection signal indicating the distance from one end is output. (2) Comparison of the levels of the two pilot signals is as follows:
A signal for determining the presence or absence of a point in time when the magnitude relationship between the amplitudes of the two pilot signals to be compared is reversed, a signal for determining the magnitude of the amplitudes of the two pilot signals when there is no reversal, and a signal for determining the magnitude of the amplitude of the two pilot signals when the reversal occurs. is characterized in that the determination is made based on the magnitude of the amplitudes of the two pilot signals at a time before or after the time when the magnitude relationship is reversed after the amplitudes of the two pilot signals match and 1ζ. A method for detecting a stop position of a magnetic tape according to claim 1.

Claims (2)

[Claims] (1) The four video tracks of the magnetic tape are projected in one period to each of the four video tracks (1st, 2nd, 3rd, and 4th signals with different frequencies along with 9 signals).
In a magnetic recording/reproducing apparatus that sequentially records pilot signals, the first, third, or second pilot signals included in the signals reproduced by two magnetic heads each having a different azimuth from each other. The levels of the fourth two pilot signals are detected separately, and based on the result of comparing the levels of the two pilot signals and the magnetic head switching signal, the stop position of the magnetic tape is determined by the track pitch of the one cycle. It outputs a signal indicating which of the four areas the magnetic tape is located in, and also outputs a signal indicating which area the magnetic tape is located in in two predetermined areas among the four areas. A method for detecting a stop position of a magnetic tape, characterized in that a detection signal indicating the distance is output. (2) Comparison of the levels of the two pilot signals is as follows:
A signal for determining the presence or absence of a point in time when the magnitude relationship between the amplitudes of the two pilot signals to be compared is reversed, a signal for determining the magnitude of the amplitudes of the two pilot signals when there is no reversal, and a signal for determining the magnitude of the amplitude of the two pilot signals when the reversal occurs. The patent is characterized in that after the amplitudes of the two pilot signals match, the determination is made based on the magnitude of the amplitudes of the two pilot signals before or after the time when the magnitude relationship is reversed. A method for detecting a stop position of a magnetic tape according to claim 1.