JPH0316706B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic tape stop position detecting device, and more particularly to a magnetic tape stop position detecting device for magnetic recording and reproduction in which a pilot signal is superimposed and recorded on a video signal of a video track for tracking. In a rotating magnetic head type VTR, four pilot signals f ₁ , f ₂ , f ₃ , and f ₄ that are generated in synchronization with the rotation of the magnetic head and have different frequencies should be recorded for tracking during playback. Multiplexed with video signal and recorded sequentially on each video track,
It is being regenerated. That is, if there is a track shift during playback, two pilot signals are obtained: the pilot signal of the track being played back and the pilot signal due to crosstalk from the adjacent track to which the head approaches, and the relationship between the track and the magnetic head can be detected. Can be done. These previously written pilot signals are used to detect the positional relationship between the magnetic head and the video track, that is, the tape position of the magnetic tape, not only during tracking but also during playback and when the magnetic tape is stopped. If it can also be used,
Shortening the pull-in time of the servo for magnetic tape travel control when transitioning from still image playback to normal playback, maintaining continuity of pilot signals between previously recorded video tracks and newly recorded video tracks during splicing, The present invention can be used for magnetic tape feeding control to obtain noiseless still images, etc., to improve the efficiency of these operations, and improve the performance of the magnetic recording/reproducing device. Therefore, an object of the present invention is to provide a magnetic tape stop position detection method that can detect the position of a magnetic head when the magnetic tape is stopped from playback by using a pilot signal recorded on a track. It is to provide. The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings. To summarize the invention, in a magnetic recording/reproducing apparatus that sequentially records four pilot signals f ₁ to _{f 4} having different frequencies on each video track of a magnetic tape by superimposing them on a video signal, The first and third pilot signals are separated and detected from the reproduced signal on which the pilot signal obtained from the tape is superimposed, and their amplitudes are compared to form a first comparative output, and the second and fourth pilot signals are also detected. A second comparative output is generated by comparing the amplitudes of the magnetic head, and the stop position of the magnetic head is detected by determining the relationship between the signal levels of the first and second comparative outputs. 1 to 5 are diagrams for explaining embodiments of the present invention. First, the relationship between the video track on the magnetic tape surface and the travel locus of the magnetic head will be explained with reference to FIG. Video tracks 2a, 2 on magnetic tape 1
2b, 2c, 2d, and the magnetic head 3a (the magnetic head 3b is not shown) when the magnetic tape 1 is in a stopped state. The magnetic tape 1 is inserted into the magnetic head 3a,
3b runs in the direction shown by arrow B, and tracks 2a to 2 of video tracks 2a to 2d
Let T be the track width of d, W be the head width of the magnetic heads 3a and 3b, and P be the track pitch in the longitudinal direction of the magnetic tape 1. The traveling trajectories of the magnetic heads 3a, 3b are expressed using the traveling trajectories 4a, 4b, 4c at the lower end, upper end, and center of the magnetic heads 3a, 3b. In addition, video tracks 2a to 2d
, the pilot signals f ₁ to _{f 4} are multiplexed with the video signal and recorded sequentially on each track.
and 2c and video tracks 2b and 2d are recorded using the same magnetic head, and these two magnetic heads have different azimuths. Switching points 5a and 5b for the magnetic heads 3a and 3b during reproduction are set near both ends of the magnetic tape 1, respectively. The stop position of the magnetic tape 1 is set by the magnetic heads 3a, 3.
Center travel locus 4c of b and switching point 5
Now, the x-coordinate of the magnetic tape 1 is taken as the longitudinal direction, and the zero point is the point where the central traveling locus 4c of the video track 2d intersects with the switching point 5a. The stop position of the magnetic tape 1 shown in FIG. 1 is at x=1.9p. Since the video tracks 2a to 2d are recorded periodically with respect to the pilot signals _f1 to _f4 , with four tracks as one cycle, by using the pitch p,
=0 to 4p can represent all stop positions. The pilot signals f ₁ to _{f 4} are signals each having a different constant frequency in a frequency range lower than that of the low frequency conversion color signal, and between the mutual frequencies |f ₁ −f ₂ |
≒｜f ₃ −f ₄ ｜=f _a , |f ₁ −f ₄ |≒｜f ₂ −f｜=f _b , f _a
It is a signal of approximately 100kHz to 200kHz that satisfies the condition ≠ f _b . For example, f ₁ , f ₂ , f ₃ , f ₄ are 102kHz in order,
118kHz, 164kHz, and 148kHz are proposed. Further, the frequency difference _fa and f _b are several tens of kHz (in the above example, they are 16 kHz and 46 kHz, respectively). As mentioned above, the pilot signals f ₁ to _{f 4} have lower frequencies than the video signals, 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. be. Regarding the stop magnetic tape 1 as described above, the second
Figure a shows the stop position of the magnetic tape 1, that is, x=
1.9p, the reproduction track widths T ₁ and T ₃ of the video tracks 2a and 2b traced by the magnetic heads 3a and 3b during one field period are shown. 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 t _f , where t/t _f =O, 1 indicates when the head centers of the magnetic heads 3a and 3b pass through the switching points 5a and 5b, respectively. corresponds to the time it takes to Further, in the figure, the head ends W of the magnetic heads 3a and 3b are designed to be 1.6 times the track width T.
FIG. 2b shows the reproduction track widths T ₂ and T ₄ of the video tracks 2b and 2d at the same magnetic tape stop position as in FIG. 2a. In the same figure,
At the time of t/t _f =0.9, the values of the reproduction track widths T ₂ and T ₄ match, and the magnitude relationship is reversed. As can be seen from the examples shown in FIGS. 2a and 2b, there are two playback track widths T ₁ , T ₃ and T ₂ , depending on the magnetic tape stop position.
The T ₄ relationship has a unique magnitude relationship. Figure 3 shows the magnitude relationship of the reproduction track widths T ₁ and T ₃ and the magnitude relationship of T ₂ and T ₄ in one field period with respect to the stop position x of the magnetic tape based on the above definition. be. Here, 0<x<
The area of p is X ₁ , the area of p≦x≦2p is X ₂ , 2p<x
Let the region <3p be X ₃ and the region 3p≦x≦4p be X ₄ . As is clear from the figure, when comparing the two sets of reproduction track widths T ₁ and T ₃ and T ₂ and T ₄ during one field period, in any of the regions X ₁ to _{X 4} , one set is There is a set in which the size relationship of the playback track width is not reversed, and by knowing the size of the playback track width in this set that is not reversed, it is possible to determine whether the stop position x of the magnetic tape is in the area _X1 , _X2 , _X3 , or _X4. It is possible to determine whether there is for example,
When comparing playback track widths T ₁ and T ₃ , T ₁ is always
If T is ₃ or more, the stop position x of the magnetic tape is area X ₂
, and if T ₁ is always less than or equal to T ₃ , the stop position x
is in region X ₄ . Alternatively, by knowing the magnitude relationship of the playback track width and the presence or absence of the point at which the magnitude relationship is reversed, the stop position x of the magnetic tape 1 _can be set to
It is also possible to determine which region of X ₄ it is in. However, in FIG. 3, in area X ₂ ,
At the timings of (x=p, t=t _f ) and (x=2p, t=O), the playback track width becomes T ₁ =T ₃ , and (x=p, t=O) and (x=2p , t=
t _f ), the playback track width becomes T ₂ =T ₄ . Also in region X ₄ , when (x=3p, t=t _f ) and (x=4p, t=O), the reproduction track width is T ₁ =
T ₃ , (x=3p, t=O) and (x=4p,
When t=t _f ), the reproduction track width becomes T ₂ =T ₄ . Here, since the pilot signals f ₁ , f ₂ , f ₃ , and f ₄ are written superimposed on the video track, the reproduction track widths T ₁ , T ₂ , T ₃ , and T ₄ are the same as those of the magnetic head 3.
Pilot signal included in the reproduced signals of a and 3b
It has a proportional relationship with the amplitude of f ₁ , f ₂ , f ₃ , and f ₄ respectively. This invention provides the above-mentioned proportional relationship between the reproduction track width and the amplitude of the pilot signal, and the first
The stop position x of the magnetic tape 1 and the playback track widths T ₁ , T ₂ ,
The position of the magnetic tape is detected using the correspondence between T ₃ and T ₄ . FIG. 4 is a block diagram showing an example of the present invention. In the figure, the input end of the balanced modulator 6 has rotating magnetic heads 3a, 3b containing pilot signals.
At the same time, the frequency |f ₁ −
f ₂ ｜≒｜f ₃ −f ₄ ｜=f _a or ｜f ₁ −f ₄ ｜≒｜f ₂ −f ₃
In order to form a beat signal of |=f _b (hereinafter referred to as beat signals f _a and f _b ), the pilot signal f ₁ or
f ₂ is input in response to switching control of a switch circuit 12, which will be described later. The output signal of the balanced converter 6 has a center frequency equal to the frequencies f _a and f _b of the beat signal.
The beat signal components contained in the output signal of the balanced modulator 6 are inputted to band filters 7a and 7b set respectively to separate the beat signal components. The separated beat signals f _a and f _b are respectively detected by detectors 8 a and 8 b into signals having corresponding amplitudes, and are applied to the input terminal of a comparator 9 to compare the levels between the two input signals. Ru. Based on the comparison result, an output signal O ₁ of high potential H or low potential L is derived to the first output terminal 14 . This output signal O ₁ indicates the stop position of the magnetic tape 1 depending on whether the pilot signal input to the balanced modulator 6 is f ₁ or f ₂ under the control of the switch circuit 12. I will do it. The output signal O ₁ is also applied to a circuit for forming a control signal for a switch circuit 12 for controlling whether the pilot signal input to the balanced modulator 6 is selected as f ₁ or f ₂ . A signal for controlling the switch circuit 12 is provided by a pulse generating circuit 10 to which the output signal _O1 of the comparator 9 is input, and a D-flip-flop 11. That is, the pulse generation circuit 10 generates positive pulses at the rise and fall of the input signal, and the D-type flip-flop 11
input to trigger terminal T of. The D-flip-flop 11 has the data terminal D held at the "H" level and operates when the trigger signal rises, and is in the reset state when the reset terminal R is "H", that is, the output terminal Q becomes "L". This output signal O ₂
is led out to the second output terminal 15 and is also given to the switch circuit 12, and the switch circuit 1
2 selects the pilot signal _f2 when the output signal _O2 is "L" depending on the state of the output signal _O2 , and sets it to "H".
In this state, f ₁ is selected and supplied to the balanced modulator 6. The reset terminal R of the D-flip-flop 11 is supplied with a signal obtained by inverting the detection command by an inverter 13. Next, the operation of the magnetic tape stop position detection device constructed as described above will be explained. Figure 5 shows a time chart during detection operation,
A case is shown in which the stop position of the magnetic tape 1 is x=2.5p. Assume that a stop position detection command is issued at time t=p ₀ as shown in FIG. 5a. FIG. 5b shows a head switching signal for switching the magnetic heads 3a and 3b. Before this time, the D-flip-flop 11 is in a reset state and the output terminal Q is at an L level. The switch circuit 12 therefore outputs a pilot signal f ₂ which is input to the balanced modulator 6. Re-signals from the rotating magnetic heads 3a and 3b are also input to the balanced modulator 6, and as mentioned above, the re-signals generated by the pilot signals f ₁ and f ₂ included in the re-generated signals and the input pilot signal f ₂ are input to the balanced modulator 6. The beat signal f _a ,
Outputs a signal containing f _b . beat signal here
The amplitudes of f _a and f _b match the amplitudes of pilot signals f ₁ and f ₂ included in the reproduced signal. The reproduced signal is a pilot signal after amplifying the signal reproduced by the rotating magnetic heads 3a and 3b.
The filter may be passed through a filter having f ₁ , f ₂ , f ₃ , and f ₄ within the pass band. The bandpass filters 7a and 7b separate and detect beat signals whose frequencies are fa _{and fb} from the output of the balanced modulator 6, respectively, and the detectors 8a and 8b output the amplitudes of the respective signals. The outputs of the detectors 8a and 8b are sent to the comparator 9.
is input and a size comparison is performed. Stop position is x
= 2.5p, the pilot signal f ₂ is sent to the balanced modulator 6.
While inputting t, the outputs of the detectors 8a and 8b are, for example, t=
At t ₁ they have the same value, at which point the output of comparator 9 is inverted. As in this example, if there is a point in the field period where the amplitude relationship of the beat signals f _a and f _b reverses, the field start point,
For example, the output of the comparator 9 is also inverted at t=t ₂ . Now, in synchronization with the inversion of the output of the comparator 9 at t= _t1 , the pulse generator 10 generates a pulse of positive polarity, which triggers the D-flip-flop 11 and applies it to the data terminal D. The current H is output to the output terminal Q as a signal _O2 .
When the output signal _O2 becomes H, the switch circuit 12 outputs the pilot signal _f1 . At this time, the amplitudes of the beat signals fa _{and fb} included in the output signal of the balanced modulator 6 match the amplitudes of the pilot signals f ₂ and f ₄ included in the reproduced signal. When x=2.5p, it can be seen from FIG. 3 that the amplitude of the pilot signal f ₂ included in the reproduced signal is always larger than the amplitude of f ₄ . Therefore, the comparator 9 outputs H as the output signal _O1 .
The case where the stop position is x = 2.5p has been described above _, but in this embodiment, when x is in _{the region} It becomes H. When the stop position x is in the area X ₁ , Fig. 5c,
The polarities of the signals d and e are inverted, and the output signal _O1 of the comparator 9 becomes L, and the output signal _O2 of the D-flip-flop becomes H. i.e. output signal O ₁
The output signal O ₂ is H. Further, when the stop position x is in the region _X2 or _X4 , as described above, the amplitude of the pilot signal _f1 included in the reproduced signal is greater than or equal to the amplitude of _f3 , respectively. Therefore, the output signal of comparator 9
O ₁ is not reversed. The output signal _O2 of the D-flip-flop 11 remains low. That is, when x is in the region _X2 , the output signal _O1 is H, the output signal _O2 is L, and when x is in the region _X4 , the output signal _O1 is L,
The output signal _O2 becomes L. To summarize the above relationships, in the embodiment shown in FIG. 4, as shown in the following table, the output signals O ₁ ,
Due to H and L of O ₂ , the stop position x is in the area X ₁ , X ₂ ,
It is possible to detect whether it is at X ₃ or X ₄ .

[Table] In the embodiment shown in FIG. 4, the pilot signals f ₁ and f ₂ are used as the reproduction signal and the beat signal, but other combinations, that is, f ₁ and f ₄ ,
Similar detection is possible using f ₃ and f ₂ or f ₃ and f ₄ . Furthermore, in the embodiment shown in FIG. 4, a comparison of pilot signals f ₁ and f ₃ included in the reproduced signal,
Comparisons of f ₂ and f ₄ are performed sequentially, but similar detection is possible even if both are performed in separate circuits. Furthermore, to compare the amplitudes of the pilot signals contained in the reproduced signal, the reproduced signal is input in advance to four band filters whose center frequencies are equal to the frequencies of the pilot signals f ₁ , f ₂ , f ₃ , and f ₄ . This can also be done using the results of detecting the separated outputs. As described above, according to the present invention, the stop position of the magnetic tape can be detected from the comparison output obtained by comparing the amplitudes of four pilot signals included in the reproduction signal, and the magnetic tape drive position can be detected. It is possible to improve the efficiency of travel control when conditions change, and it can also be used to maintain the continuity of pilot signals between video tracks and to control various signals to improve the performance of magnetic recording and reproducing devices. .

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the positional relationship between a magnetic tape and a magnetic head. FIG. 2 is a diagram showing changes in reproduction track width during one field period. Third
The figure shows the relationship between the magnetic tape stop position and the playback track width. FIG. 4 is a block diagram showing one embodiment of the present invention. FIG. 5 is a time chart for explaining the operation of the same embodiment. In the figure, 1 is a magnetic tape, 2a to 2d are video tracks, 3a and 3b are magnetic heads, 6 is a balanced modulator, 7a and 7b are band filters, 8a and 8
b is a detector, 9 is a comparator, and 12 is a switch circuit.

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 of different frequencies.
A magnetic tape stop position detecting device in a magnetic recording/reproducing apparatus, wherein four fourth pilot signals are sequentially recorded by a plurality of rotating magnetic heads, the first and third pilot signals included in the reproduction signal A first step that separately detects the amplitude of
a comparison means for separately detecting the amplitudes of the second and fourth pilot signals included in the reproduced signal, and detecting the magnitude relationship between the two and the presence or absence of a point at which the magnitude relationship is reversed.
and a detection signal output means for inputting the outputs of the first and second comparing means and outputting a signal indicating in which region the stop position of the magnetic tape is located in a region obtained by dividing the one cycle into four equal parts. A magnetic tape stop position detection device comprising: