JPS59201258A - Detector for stop position of magnetic tape - Google Patents

Abstract

PURPOSE:To perform efficient running control when driving state of a magnetic tape are changed, by detecting a stop position of the magnetic tape from comparison outputs obtained by comparing the amplitude of four pilot signals in a reproduced signal. CONSTITUTION:The reproduced signal of a magnetic head is supplied to the input terminal of a balanced modulator 6, and a signal f1 or f2 for generating a beat signal of frequency f1-f2 f3-f4=fa or f1-f4 f2-f3=fb with a pilot sig nal in the reproduced signal is inputted thereto as well in response to the switching controller of a switch circuit 12. The output signal of the modulator 6 is separated into signals fa and fb through BPFs 7a and 7b. The signals fa and fb are supplied to detectors 8a and 8b to generate signals with corresponding amplitudes, whose levels are compared with each other by a comparator 9. An output signal O1 based upon the comparison result appears at an output terminal 14. This signal O1 indicates the stop position of the magnetic tape according to whether the pilot signal inputted to the modulator 6 is f1 or f2.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 and reproduction in which a pylon 1 signal is superimposed and recorded on a video signal of a video track for tracking. The present invention relates to a detection device.

In a rotating magnetic head type VTR, four pilot signals f, , f with different frequencies are generated in synchronization with the rotation of the magnetic head for tracking during playback.
2. It is common practice to multiplex f, , f, with a video signal to be recorded, sequentially record it on each video track, and reproduce it. In other words, if there is a track misalignment 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 is approaching, and the relationship between the track and the magnetic head is detected. be able to.

These pilot signals that have already been written affect the positional relationship between the magnetic head and the video track, and the size 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 for position detection, it can reduce the pull-in time of the magnetic tape travel control servo when transitioning from still image playback to normal playback, and it can also be used to detect the gap between an already recorded video track and a newly recorded video track during splicing. It is possible to improve the efficiency of these operations by maintaining the continuity of pilot signals, controlling magnetic tape feeding to obtain noiseless still images, etc., and improving 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 during playback and when the magnetic tape is stopped, using pilot signals recorded on tracks. 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, each video track of a magnetic tape has four pilot signals f1 each having a different frequency.
In a magnetic recording and reproducing device that sequentially records f4 by superimposing it 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 stopped magnetic tape is superimposed, and the first and third pilot signals are detected separately. Compare the amplitude and
Similarly, the second and fourth pilot signals are separately detected, their amplitudes are compared to form a second comparison output, and the relationship between the signal levels of these first and second comparison outputs is determined. The stop position of the magnetic head is detected by determining the position of the magnetic head.

1 to 5 are diagrams for explaining the present invention in detail.

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 trunks 2a, 2b, 2c, 2d, , 1 on magnetic tape 1
5 and the magnetic head 3a when the magnetic tape 1 is stopped.
(The FJ air head 3b is not shown) is a diagram schematically showing the relationship. The magnetic tape 1 is moved in the direction indicated by arrow A.
Magnetic head 3a.

3b runs in the direction shown by arrow B, and the track width of video tracks 2a to 2d is set to T1 magnetic head 3.
Let the head widths of a and 3b be W1, and the trunk pitch in the longitudinal direction of the magnetic tape 1 be P. The running trajectory of the magnetic heads 3a, 3b is shown as a running trajectory 4a at the lower end, upper end, and center of the magnetic heads 3a, 3b.

4, b, and 4c. Note that pilot signals f, -f4 are sequentially recorded on the video tracks 2a to 2d by being multiplexed with the video signal, and the video trunks 2a and 20 and the video tracks 2b and 2d are recorded using the same magnetic head, respectively. These two magnetic heads have different azimuths. Switching points 5a and 5b of the magnetic heads 3a and 3b during playback are located near both ends of the magnetic tape 1.
are set 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, 3b and the switching point 5a, and now the x coordinate of the magnetic tape 1 is taken as the longitudinal direction, and the zero point is the center run of the video track 2d. It is assumed that the locus 4C intersects with the switching point 5a. The stop position of the magnetic tape 1 shown in FIG. 1 is at x=1.9p.

Video tracks 2a-2d are pylon 1-signal f.

~f is recorded periodically with 4 tracks as one period, so by using the pitch p, x=O
~4p can represent all stop positions.

The pilot signals f1 to f4 are signals each having a different constant frequency in a frequency range roughly lower than that of the low-pass conversion color signal, and 1ft-T21=lfs between the mutual frequencies.
r, 1=ri, lf+ f41 If 2 f
It is a signal of about 100 kHz to 200 kHz2 that satisfies the conditions that 31=fh and fa-≠f. For example, f, , T2. 1 in the order of f, , T4
021., Hz, 118 kHz, 164 kHz,
148kl-12 has been proposed. Also, the frequency difference f(.

fb is several tens of kHz (in the above example, t is respectively; hl 6 kHz and 46 kHz). As mentioned above, since the pilot signals f1 to f4 have 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 having an azimuth different from that during recording.

Regarding the stop magnetic tape 1 as described above, FIG. 2(a)
is the stop position of the magnetic chip 71, that is, ×-1, 91), and the reproduction track iT of the video tracks 2a, 2b that the magnetic heads 3a, 3b trace in one field period,
, T.

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 tj, and t/J = 0.1 means the magnetic head 3a,
The center of the head of 3b is the switching point 5a,
This corresponds to the time it takes to pass through 5b. In addition, in the same figure, the head ends W of the magnetic heads 3a and 3b are 1 of the track width T.
．． Designed to be 6 times larger. Figure 2(b) is Figure 2(a)
Video track 2b at the same magnetic tape stop position as
.

2d shows the reproduction track width T2, T. In the figure, at the time of t /lj =0.9, the playback track width T2. The values of T4 match and the magnitude relationship is reversed. As shown in FIGS. 2(a') and 2(b), two playback track widths T are available depending on the magnetic tape stop position.
+, Ta and T2. The relationship of T4 has an inherent magnitude relationship.

Based on the above definition, FIG. 3 shows the magnitude relationship between the reproduction 1 and rack widths T + , T 3 and T 2 during one field period with respect to the stop position X of the magnetic tape.

This shows the magnitude relationship of T. Here, O〈×〈
The area of p is X+, the area of p≦X≦2p is Xz, 20
Let the region where <x <3p be Xs, and the region where 3p≦x≦4p be X4. As is clear from the figure, the reproduction track width T and T3 and T2 and T during one field period are two.
In comparing the sizes of the pairs, there are pairs in which the magnitude relationship of the reproduction track width of one phase is not reversed in any of the regions x and x4, and by knowing the magnitude of the reproduction track width in the phase that is not reversed, the magnetic tape The stop position X is in the area X1. It is possible to determine which of X2, Xs, and X4 is present. For example, below the playback track width and T
, if T1 is always greater than or equal to 10, the magnetic tape stop position x is in the area X2, and if T is always less than T, the magnetic tape stop position x is in the area X. Or, by knowing the size relationship of the playback track width and the presence or absence of the point at which the size relationship is reversed, the stop position x of the magnetic tape 1 can be changed to
It is also possible to determine in which region of X4 the object is located.

However, in FIG. 3, in area x2, (x =
p, t = tf) and (X = 2p, t =
0), the playback track width is 1, T, =
T, and (X = p, t = O) and I = 2
p.

1=1(), the regenerated trunk width becomes T2=T4. Also in the area ×4 (X = 3p, t −1
f) and (x = 4.p, t = O), the track width of the trimmed playback is T, = T3, and (x = 3p, t
= O) and (x = 4.l), j = tf
), the reproduction track width becomes T2=T-.

Here, pilot signals f + , T2 . Since fs and fs are written in a superimposed manner on the video mill rack, the playback 1 to rack widths T, , T2 , T, , T are the same as the pyrower 1 to signal widths included in the reproduction signals of the magnetic heads 3a and 3b. @
T, ,T2. They have a proportional relationship with the amplitudes of f, , and T4, respectively.

The present invention relates to the proportional relationship between the reproduced track width and the amplitude of the pilot signal as described above, and FIG.

The stop position x of the magnetic tape 1 and the playback track width T, , T2 , T8 . explained using FIGS. 2 and 3.
The position of the magnetic tape is detected using the correspondence relationship between the magnetic tape and the magnetic tape.

FIG. 4 is a block diagram showing an example of the present invention. In the figure, the input terminal of the balanced modulator 6 is given a reproduction signal of the rotating magnetic l\rad a', 3b containing a pilot signal, and a frequency If .

r21'=1f s f4 :=L tl=C]f, -f41 If, -f31=fmu Nogo-1~
[In order to form a beat signal (hereinafter referred to as a beat signal @f^, rm), a pilot signal f or f2 is inputted in response to switching control of a switch circuit 12, which will be described later. The output signal of the balanced modulator 6 is passed through bandpass filters 7a and 7b whose center frequencies are respectively set to the frequencies fa and fb of the beat signal, and the beat signal components contained in the output signal of the balanced modulator 6 are separated. be done. separated peat 1
No. 3 f, fb are respectively detected by detectors 8a and 8b into signals having corresponding amplitudes, which are applied to the input terminal of a comparator 9 to compare the levels between the two human power signals. Based on the comparison result, an output signal 8' 0 + of a high potential (T1) or a relatively low potential (L) is outputted to the first output terminal 14.

The output signal O7 is the pilot signal input to the balanced modulator 6 based on the control of the switch circuit 120).
The position at which the magnetic tape 1 is stopped depends on whether l is trillion or f2.

The output signal 01 is also given to a circuit that forms a control signal for a switch circuit 12 for controlling whether the Byron 1 to signal input to the balanced modulator 6 is selected as f or [2. A signal for controlling the switch circuit 12 is generated by a pulse generating circuit 10 and a D-flip-flop 11 to which the output signal ◯ of the comparator 9 is input. That is, the pulse generation circuit 10 generates positive pulses at the rising and falling edges of the input signal, and the D-type flip knob 11
input to the trigger terminal of the Rae flip flop 11
is held at the data terminal r)-IJ level,
1 - Operates at the rising edge of the trigger signal, and is in the reset state when the reset terminal R is "H", that is, the output terminal Q is rL
J, and this output signal 02 is output to the second output terminal 15 and is also given to the switch circuit 12,
Depending on the state of the output signal 02, the switch circuit 12 selects the pilot signal f2 when the output signal 02 is l' L J, selects f when the output signal 02 is "H", and selects the pilot signal f2 when the output signal 02 is "H".
supply to. 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.

FIG. 5 shows the time chip p-(- during the detection operation, and shows the case where the stop position of the magnetic tape 1 is X=2.50.

Assume that a stop position detection command is issued at time j=l)o as shown in FIG. 5(a). FIG. 5(b) shows a head switching signal for switching between 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 L level. Therefore, the switch circuit 12 outputs a pilot signal f2, which is input to the balanced modulator 6. The balanced modulator 6 includes a rotating magnetic head 3a.

The reproduced signal 3b is also input, and as mentioned above, a signal containing the beat signals fe and fb generated by the pilot signals f, , f included in the reproduced signal and the input pilot signal f2 is output. .

Here, the magnitudes of the amplitudes of the beat signals fe and fb match the magnitudes of the amplitudes of the pilot signals f, f, and 'fs included in the reproduced signal. Note that the reproduced signals are pilot signals f + , f2 . The signal may be passed through a filter having fs and L within the passband in advance.

The bandpass filters 7a and 7b separate and detect the beat signals whose frequencies are fL and fL, respectively, output from the balanced modulator 6, and the detectors F3a and 13b output the amplitudes of the respective signals. The outputs of the detectors 8a and 8b are input to a comparator 9 and compared in magnitude. Stop position is X=2.5p
In the case of FIG. 5(C) while the pilot signal f2 is input to the balanced modulator 6.

As shown in (6) and (e), the outputs of the detectors 8a and 8b have the same value at, for example, 1-1, and at this point the output of the comparator 9 is inverted.

As in this example, the number [α,
If there is a point in time when the magnitude relationship of the amplitude of fb reverses,
Even at the start of the field, for example 1 = 1, the output of the comparator 9 is inverted. Now, in synchronization with the inversion of the output of the comparator 9 at -tl, the pulse generator 10 generates a pulse 4 of positive polarity, which triggers the D-flip-flop 11 and applies it to the data terminal. The output signal H is output to the output terminal Q as a signal 02. When the output signal 02 becomes T1, the switch circuit 12 outputs the pilot signal f1. At this time, the amplitudes of the beat signals ra and rh included in the output signal of the balanced modulator 6 are as follows:
This corresponds to the magnitude of the amplitude of the pilot signals f2 and f4 included in the reproduced signal. In the case of x-2, 5p, it can be seen from FIG. 3 that the amplitude of the signal f2 from pylon 1 included in the reproduced signal is always larger than the amplitude of f4. Therefore, the comparator 9 outputs the output signal O
4 and outputs "F". The stopping position is x=2.5p
We will explain the case of t), but in this example (in case of
is in the region X, it operates in the same way, and the output terminals 14,
Signals 07.02 derived from signal 07.15 both become H.

When the stop position X is in the area X, Fig. 5(C), (
The polarities of the signals d) and (e) are inverted, and the output signal 01 of the comparator 9 becomes high, and the output signal 02 of the D-flip-flop becomes H. That is, the output signal 01 is high and the output signal 02 is high.

Further, when the stop position x is in the area x2 or x4, the amplitudes of pilot 1' and signal f included in the reproduced signal are respectively greater than or less than the amplitude of f, as described above. Therefore, the output signal O1 of the comparator 9 is not inverted.

The output signal 02 of the D-flip-flop 11 remains L.
be. That is, when X is in the region M X 2, the output signal @O1 becomes H, the output signal @02 becomes L, and the output signal @01 in region I4X4 becomes L1, and the output signal 02 becomes L.

To summarize the above relationships, in the practical example shown in Fig. 4, as shown in the following table, the H and L output signals O4 and 02 after one field period has elapsed since the detection command was issued. Therefore, the stop position x is in the area X+, Xz, X8. In the embodiment shown in FIG. Similar detection is possible using straws fl and f, f, and fz, and f8 and f4.

Furthermore, in the embodiment shown in FIG. 4, the comparison of pilot signals f and f included in the reproduced signal and
Although the comparisons are made sequentially, the same detection can be achieved even if the two are performed using separate circuits.

Furthermore, to compare the amplitudes of the pilot signals included in the reproduced signal, the reproduced signal was input in advance to four bandpass filters whose center frequencies were equal to the frequencies of the pilot signals f + , fz , fa , and fs and separated. This can also be done using the results of detecting the output.

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 reproduced signal, and the stop position of the magnetic tape 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, improving the performance of magnetic recording and reproducing devices. .

[Brief explanation of drawings]

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. FIG. 3 is a diagram showing the relationship between the magnetic tape stop position and the playback 1 to rack 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, 28 to 2d are video tracks, 3a and 3b are magnetic heads, 6 is a balanced modulator, and 7 is a magnetic tape.
'a and 7b are bandpass filters, 8a and 8b are detectors, 9 is a comparator, and 12 is a switch circuit. Agent Masu Oiwa 2°") 1. 1. (b) ■- ot/lJ-↑"01

Claims (4)

[Claims] (1) In synchronization with the rotation of the rotating magnetic head, the first. Second. The third and fourth four signals D? t' is multiplexed with the video signal, sequentially recorded on a magnetic tape, and played back. a first means for detecting 3 minutes per minute; a second means for detecting and covering the fourth Byronto signal from the Kiku2J3 included in the reproduction signal of the rotating magnetic head; and outputs of the first and second means of n5. is input, and the output () corresponding to the stop position of the tape is generated based on the power of both people.
A magnetic tape stop position detection device, comprising: a third means for outputting ξ. (2) The third means includes a function of detecting the magnitude of the amplitude of the input signal as well as the presence or absence of a point at which the magnitude relationship of the amplitudes is reversed. Device. (3) The third means includes a pyrower 1 to a signal separation circuit that separates the four pilot signals based on the outputs of the first and second means, respectively. magnetic tape stop position detection device. (4) The first and second means compare the amplitudes of the pilot signals based on the amplitudes of the beat signals formed from the pilot signal and the reproduced signal, which have different frequencies from those of the Pylob 1 signal to be compared. A magnetic tape stop position detection device according to any one of claims 1 to 3.