JPH07118116B2 - Magnetic tape stop position detection device for magnetic recording / reproducing device - Google Patents

Description

The present invention relates to a magnetic tape stop position detection device, and more particularly to a magnetic tape stop position detection device for magnetic recording / reproduction in which a pilot signal is superposed on a video signal of a video track for recording. It is about.

In a rotary magnetic head type VTR, four pilot signals f ₁ , f ₂ with different frequencies, which are generated in synchronization with the rotation of the magnetic head, are used for tracking during reproduction.
It is practiced to multiplex f ₃ and f ₄ with a video signal to be recorded, and sequentially record and reproduce on each video track. That is, if there is a track deviation during reproduction, two signals, the pilot signal of the track being reproduced and the pilot signal due to crosstalk from the adjacent track to which the head approaches, can be obtained, and the relationship between the track and the magnetic head can be detected. You can

Such a pilot signal already written is detected not only at the time of tracking but also at the time of reproduction and when the magnetic tape is stopped, that is, the positional relationship between the magnetic head and the video track, that is, the tape position detection of the magnetic tape. If it can also be used for, it is possible to shorten the pull-in time of the servo for controlling the running of the magnetic tape during the transition from still image playback to normal playback, and to use the pilot between the recorded video track and the newly recorded video track during joint recording. It is possible to improve the operation efficiency of the magnetic recording / reproducing apparatus by maintaining the continuity of signals and controlling the magnetic tape feeding to obtain a noiseless still image.

Therefore, an object of the present invention is to provide a magnetic tape stop position detection device capable of detecting the position of a magnetic head in a state where the magnetic tape is being reproduced and stopped using a pilot signal recorded on a track. Is to provide.

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

To summarize the present invention, four pilot signals f _{1 to} f ₄ having different frequencies in synchronization with the rotation of the rotary magnetic head are (f ₁ , f ₂ ), (F ₂ , f ₃ ), (f ₃ ,
f ₄₎ and (f _4, in adjacent tracks on the magnetic tape in combination f _1), multiplexed sequentially recorded to the video signal to be recorded, the magnetic tape stop position detecting apparatus of a magnetic recording and reproducing apparatus which reproduces And each pilot signal is | f ₁ −
_{f 2 | ≒ | f 3 -f} 4 | = f a and _{| f 1 -f 4 | ≒ |} f 2 -f 3 | =
a pilot signal having a frequency difference of f _b, which is included in the signals sequentially reproduced by the rotary magnetic head;
First beat signal level detecting means for detecting a first beat signal having _a frequency difference f _a obtained from a reference pilot signal different from the reproduced pilot signal and outputting the first detected signal; A second beat signal having a frequency difference f _b obtained from the reference pilot signal different from the pilot signal included in the signal sequentially reproduced by the magnetic head and the reproduced pilot signal is detected, and the second detection is performed. Second beat signal level detecting means for outputting a signal,
The output signals from the first and second beat signal level detecting means are compared with each other, and if the magnitude relationship is reversed, the comparing means for inverting the output value at the L or H level, and L or Switching signal generating means for outputting a signal reset to any one of the H levels and inverting its output level by a pulse signal when the output of the comparing means is inverted; and among the first to fourth pilot signals, And a signal switching means for selecting either one of the two pilot signals and the two signals having the same frequency based on the output of the switching signal generating means and outputting the selected pilot signal as the reference pilot signal. Magnetic recording means for detecting the stop position of the magnetic tape from the level of the output signal of the means and the level of the output signal of the switching signal generating means. A magnetic tape stop position detecting device of the reproduction apparatus.

1 to 5 are views for explaining an embodiment of the present invention.

First, the relationship between the video track on the magnetic tape surface and the running track of the magnetic head will be described with reference to FIG. FIG. 3 is a diagram schematically showing a relationship between video tracks 2a, 2b, 2c, 2d on the magnetic tape 1 and a magnetic head 3a (the magnetic head 3b is not shown) when the magnetic tape 1 is stopped. The magnetic tape 1 travels in the direction indicated by the arrow A, the magnetic heads 3a and 3b travel in the direction indicated by the arrow B, and the video tracks 2a.
The track width of 2d is T, the head width of the magnetic heads 3a and 3b is W, and the track pitch in the longitudinal direction of the magnetic tape 1 is P. The traveling loci of the magnetic heads 3a, 3b are represented by the traveling loci 4a, 4b, 4c of the lower end, upper end and center of the magnetic heads 3a, 3b. Note that the video track 2a~2d pilot signals f ₁ ~f ₄ multiplexes the video signal is sequentially recorded in each track, video track 2a and 2c and video track
2b and 2d are recorded by the same magnetic head, and those two magnetic heads having different azimuths are used. Switching points 5a and 5b of the magnetic heads 3a and 3b at the time of reproduction are set at positions near both ends of the magnetic tape 1, respectively.

The stop position of the magnetic tape 1 is represented by the intersection of the center running locus 4c of the magnetic heads 3a and 3b and the switching point 5a. Now, with the x coordinate of the magnetic tape 1 as the longitudinal direction, the zero point is the center running of the video track 2d. It is assumed that the locus 4c intersects the switching point 5a. The stop position of the magnetic tape 1 shown in FIG. 1 is in the state of x = 1.9p. Since video track 2a~2d are periodically recorded as one cycle four tracks with respect to the pilot signals f ₁ ~f _4, that represent all the stop positions x = 0~4p by using the pitch p it can.

The pilot signals f _{1 to} f ₄ are signals each having a different constant frequency in a frequency region lower than that of the low-pass conversion color signal, and | f ₁ −f ₂ | ≈ | f ₃ −f ₄ between the mutual frequencies. ｜ ＝ f _a , |
Satisfies the conditions f ₁ −f ₄ | ≈ | f ₂ −f ₃ | = f _b , f _a ≠ f _b
It is a signal of about 100 kHz to 200 kHz. For example, f ₁ , f ₂ ,
102 kHz, 118 kHz, 164 kHz, and 148 kHz have been proposed in the order of f ₃ and f ₄ . Further, the frequency differences f _a and f _b are several tens of kHz (16 kHz and 46 kHz respectively in the above example). Since the pilot signals f _{1 to} f ₄ have a lower frequency than the video signal as described above, the influence of the azimuth effect of the magnetic heads 3a and 3b is small, and the pilot signals f _{1 to} f ₄ can be reproduced by a magnetic head having an azimuth different from that at the time of recording.

FIG. 2 (a) of the stop magnetic tape 1 as described above.
Shows the reproduction track widths T ₁ and T ₃ of the video tracks 2a and 2b traced by the magnetic heads 3a and 3b for one field period at the stop position of the magnetic tape 1, that is, in the state of x = 1.9p. Here, the reproduction track width means the width of the overlapping portion of the magnetic head and the video track. In the figure, the horizontal axis is the time t normalized by one field time t _f , and t / t _f = 0.1 is the time when the head centers of the magnetic heads 3a and 3b pass through the switching points 5a and 5b, respectively. Equivalent to. Further, in the figure, the head end W of the magnetic heads 3a and 3b is designed to be 1.6 times the track width T. Second
FIG. 2B shows the reproduction track widths T ₂ and T ₄ of the video tracks 2b and 2d in the same magnetic tape stop position as in FIG. 2A. In the figure, the values of the reproduction track widths T ₂ and T ₄ match at the time of t / t _f = 0.9, and the magnitude relationship is reversed. As can be seen from the illustrated FIGS. 2A and 2B, two reproduction track widths T ₁ , depending on the magnetic tape stop position,
The relationship between T _3, T ₂ , and T ₄ has its own size relationship.

FIG. 3 shows the relationship between the reproduction track widths T ₁ and T _{3 and} the relationship between T ₂ and T ₄ with respect to the stop position x of the magnetic tape in one field period based on the above definition. is there. Here, the region of 0 <x <p is X ₁ , the region of p ≦ x ≦ 2p is X ₂ , the region of 2p <x <3p is X ₃ , and the region of 3p ≦ x ≦ 4p is
X ₄ As is clear from the figure, in the comparison of the size of the two sets of the reproduction track widths T ₁ and T ₃ and T ₂ and T ₄ in one field period, in any of the regions X _{1 to} X ₄ , one set There is a group that does not reverse the size relationship of the playback track width of
By knowing the size of the reproduction track width in this non-reverse set, the stop position x of the magnetic tape is determined to be the region X ₁ , X ₂ , X ₃ ,
It is possible to determine in which of X ₄ . For example, in the comparison between the reproduction track widths T ₁ and T ₃ , if T ₁ is always T ₃ or more, the magnetic tape stop position x is in the area X ₂ , and if T ₁ is T ₃ or less, the stop position x is always the area. Located at X ₄ . Alternatively, it is possible to determine whether the stop position x of the magnetic tape 1 is in the area X _{1 to} X ₄ by knowing the magnitude relationship between the reproduction track widths and the time point at which the magnitude relationship is reversed.

However, in FIG. 3, in the region X ₂ , (x = p, t
= T _f ) and (x = 2p, t = 0) timing, the reproduction track width becomes T ₁ = T ₃ , and (x = p, t = 0) and (x = 2p, t = t _f ). When, the reproduction track width becomes T ₂ = T ₄ . Also in the region X ₄ , (x = 3p, t = t _f ) and (x
= 4p, t = 0), the reproduction track width is T ₁ = T ₃ ,
(X = 3p, t = 0 ) and (x = 4p, t = t f) reproduction track width when becomes T ₂ = T _4.

Here, since the pilot signals f ₁ , f ₂ , f ₃ , f ₄ are written while being superimposed on the video track, the reproduction track width
T ₁ , T ₂ , T ₃ , and T ₄ have a proportional relationship with the amplitudes of the pilot signals f ₁ , f ₂ , f ₃ , and f ₄ included in the reproduced signals of the magnetic heads 3a and 3b, respectively.

The present invention relates to the proportional relationship between the reproduction track width and the amplitude of the pilot signal as described above, and the stop position x and the reproduction track width T of the magnetic tape 1 described with reference to FIGS. 1, 2, and 3. The position of the magnetic tape is detected using the correspondence with ₁ , T ₂ , T ₃ , and T ₄ .

FIG. 4 is a block diagram showing an example of the present invention. In the figure, the reproduction signal of the rotary magnetic heads 3a and 3b containing a pilot signal is applied to the input terminal of the balanced modulator 6, and a frequency | f ₁ − is generated between the reproduction signal and the pilot signal included in the reproduction signal. f ₂ ｜ ≒ ｜ f ₃ −f ₄ ｜ ＝ f _a or ｜ f ₁ −f ₄ ｜
_{≒ | f 2 -f 3 | =} f b of the beat signal (hereinafter beat signal f _a, f _b
Pilot signal f ₁ or f ₂
Are input in response to the switching control of the switch circuit 12 described later. The output signal of the balanced modulator 6 is input to the bandpass filters 7a and 7b whose center frequencies are set to the frequencies f _a and f _b of the beat signal, and the beat signal component included in the output signal of the balanced modulator 6. Are separated. The separated beat signals f _a and f _b are detected by the detectors 8a and 8b, respectively, into signals having the corresponding amplitudes, which are applied to the input terminals of the comparator 9 to compare the levels of the two input signals. It Output signal O _{1 of} high potential (H) or low potential (L) based on the comparison result
To the first output terminal 14. This output signal O ₁ means the stop position of the magnetic tape 1 depending on whether the reference pilot signal input to the balanced modulator 6 under the control of the switch circuit 12 is f ₁ or f _2. It will be.

The output signal O ₁ is also given to a circuit forming a control signal of the switch circuit 12 for controlling whether the reference pilot signal input to the balanced modulator 6 is f ₁ or f ₂ .
The signal for controlling the switch circuit 12 is composed of the pulse generation circuit 10 to which the output signal O ₁ of the comparator 9 is input and the D-flip-flop 11. That is, the pulse generation circuit
Reference numeral 10 generates a positive pulse at the rising and falling edges of the input signal and inputs it to the trigger terminal T of the D-type flip-flop 11. The D-flip-flop 11 has the data terminal D held at "H" level, operates at the rising edge of the trigger signal, and is in a reset state when the reset terminal R is "H", that is, the output terminal Q is "L". , This output signal
O ₂ together with derived to the second output terminal 15, also applied to the switching circuit 12, the switch circuit 12 is a pilot signal f ₂ is the output signal O ₂ by the state of the output signal O ₂ in the state of "L" Then, f ₁ is selected in the “H” state and supplied to the balanced modulator 6. The reset terminal R of the D-flip-flop 11 is given a signal obtained by inverting the detection command by the inverter 13.

Next, the operation of the magnetic tape stop position detecting device configured as described above will be described.

FIG. 5 shows a time chart during the detection operation, and shows a case where the magnetic tape 1 is stopped at x = 2.5p.

It is assumed that a stop position detection command is issued at time t = t ₀ as shown in FIG. FIG. 5 (b) shows the magnetic heads 3a, 3
This is a head switching signal for switching b. D before this time
The flip-flop 11 is in the reset state and the output terminal Q
Is L. Therefore, the switch circuit 12 outputs the reference pilot signal f _2, which is input to the balanced modulator 6. The reproduction signals of the rotary magnetic heads 3a and 3b are also input to the balanced modulator 6, and as described above, they are generated by the pilot signals f ₁ and f ₃ included in the reproduction signals and the input reference pilot signal f _2. A signal including the beat signals f _a and f _b is output. Here, the amplitudes of the beat signals f _a and f _b match the amplitudes of the pilot signals f ₁ and f ₃ included in the reproduced signal. The reproduction signal is a rotary magnetic head.
3a, after amplification the signal reproduced by 3b, the pilot signals _{f 1, f 2, f 3} , f 4 may be such that the filtered beforehand with the the passband.

The band-pass filters 7a and 7b separate and detect beat signals whose frequencies are f _a and f _b , respectively, from the outputs of the balanced modulator 6, and the detectors 8a and 8b are detected.
Outputs the amplitude of each signal. The outputs of the detectors 8a and 8b are input to the comparator 9 for magnitude comparison. When the stop position is x = 2.5p, while the reference pilot signal f ₂ is being input to the balanced modulator 6, FIG. 5 (c), (d),
As shown in (e), the detector 8a, the output of 8b are the same value, for example, in t = t _1, the output of the comparator 9 at this point is inverted. When there is a point in time when the magnitude relationship between the amplitudes of the beat signals f _a and f _b is reversed within the field period as in this example, the output of the comparator 9 is also reversed at the field start point, for example, t = t ₂ . Now, in synchronism with the inversion of the output of the comparator 9 at t = t ₁ , the pulse generator 10 generates a positive pulse, which triggers the D-flip-flop 11 to be applied to the data terminal D. Is output to the output terminal Q as a signal O ₂ . Output signal O ₂
When becomes H, the switch circuit 12 outputs the reference pilot signal f ₁ . At this time, the amplitudes of the beat signals f _a and f _b 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 reproduction signal.
When x = 2.5p, the amplitude of the pilot signal f ₂ included in the reproduced signal is always larger than the amplitude of f ₄ from FIG. Therefore, the comparator 9 outputs H as the output signal O ₁ . The case where the stop position is x = 2.5p has been described above, but in this embodiment, when x is in the region X ₃ , the same operation is performed, and the signals O ₁ and O ₂ derived at the output terminals 14 and 15 are Both become H.

When the stop position x is in the area X ₁ , FIG. 5 (c),
The polarities of the signals (d) and (e) are inverted, and the output signal O ₁ of the comparator 9 is L and the output signal O ₂ of the D-flip-flop is H. That is, the output signal O ₁ is L, the output signal O ₂
Is H.

When the stop position x is in the area X ₂ or X ₄ , the amplitude of the pilot signal f ₁ included in the reproduced signal is equal to or larger than the amplitude of f ₃ , respectively, as described above. Therefore, the output signal O ₁ of the comparator 9 is not inverted. The output signal O ₂ of the D-flip-flop 11 remains L. That is, x
Is in the region X ₂ , the output signal O ₁ is H and the output signal O ₂ is L, and in the region X ₄ , the output signal O ₁ is L and the output signal O ₂ is L.

To summarize the above relationships, in the embodiment shown in FIG. 4, as shown in the following table, the output signals O ₁ and O ₂ after 1 field period has elapsed after the detection command is issued It is possible to detect which of the regions X ₁ , X ₂ , X ₃ and X ₄ the stop position x is in.

In the embodiment shown in FIG. 4, the reference pilot signals f ₁ and f ₂ are used as the beat signal and the reproduction signal, but other combinations, that is, f ₁ and f ₄ , f ₃ and f _{2 are used.} , F ₃ and f ₄ can be used for the same detection.

In the embodiment shown in FIG. 4, the pilot signals f ₁ and f ₃ included in the reproduced signal are compared with each other, and the comparisons of f ₂ and f ₄ are performed with each other. Even if it is performed, the same detection can be performed.

Furthermore, the amplitude comparison of the pilot signals included in the reproduced signal is performed by inputting the reproduced signal to four band-pass filters whose center frequencies are equal to the frequencies of the pilot signals f ₁ , f ₂ , f ₃ and f ₄ , respectively. Alternatively, the result obtained by detecting the separated output can be used.

As described above, according to the present invention, the stop position of the magnetic tape can be detected based on the comparison output obtained by comparing the amplitudes of the four pilot signals included in the reproduction signal, and the magnetic tape can be driven. It is possible to improve the efficiency of the traveling control when the state changes, and to improve the performance of the magnetic recording / reproducing apparatus by utilizing the control of various signals including maintaining the continuity of the pilot signal between video tracks. .

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a positional relationship between a magnetic tape and a magnetic head. FIG. 2 is a diagram showing changes in the reproduction track width during one field period. FIG. 3 is a diagram showing the relationship between the magnetic tape stop position and the reproduction track width. FIG. 4 is a block diagram showing an embodiment of the present invention. FIG. 5 is a time chart for explaining the operation of the 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 bandpass filters, 8a and 8b are detectors, 9 is a comparator, and 12 is a switch. Circuit.

Claims (1)

[Claims] 1. A first pilot signal, a second pilot signal, a third pilot signal, and a fourth pilot signal which have different frequencies in synchronization with the rotation of a rotary magnetic head.
f _{1 to} f ₄ are combinations of (f ₁ , f ₂ ), (f ₂ , f ₃ ), (f ₃ , f ₄ ) and (f ₄ , f ₁ ) in adjacent tracks on the magnetic tape, A magnetic tape stop position detecting device of a magnetic recording / reproducing device that multiplexes and sequentially reproduces a video signal to be recorded, and each pilot signal is | f ₁ −f ₂ | ≈ | f ₃ −f ₄ | =
f _a and | f ₁ −f ₄ | ≈ | f ₂ −f ₃ | = f _b, and the pilot signal included in the signals sequentially reproduced by the rotary magnetic head, and this reproduced signal. And a first beat signal level detecting means for detecting a first beat signal having _a frequency difference f _a obtained from a reference pilot signal different from the pilot signal and outputting the first detected signal; and the rotary magnetic head. A frequency difference obtained from a pilot signal included in the sequentially reproduced signal and the reference pilot signal different from the reproduced pilot signal.
a second beat signal level detecting means for detecting the second beat signal of f _b and outputting a second detected signal, and comparing the output signals from the first and second beat signal level detecting means, When the magnitude relationship is reversed, a comparison means for inverting the output value of the L or H level and a signal reset to either the L or H level based on the tape position detection command are output to invert the output of the comparison means. Switching signal generating means for inverting its output level according to the pulse signal of time, and one of two signals having the same frequency as any two pilot signals of the first to fourth pilot signals. Is selected based on the output of the switching signal generating means, and is output as the reference pilot signal. A magnetic tape stop position detecting device for a magnetic recording / reproducing apparatus, wherein a stop position of a magnetic tape is detected from a signal output means and a switching signal output means for outputting an output signal from the switching signal generating means.