JPS61229251A - Helical scan magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To detect accurately the stop position of a magnetic tape by generating a pilot signal having the same frequency as that of a pilot signal recorded on one adjacent track to a master track being traced to a pilot signal generating means is reproducing an information signal, multiplying it with a pilot signal to detect its beat component and detecting the stop position of the magnetic tape from the detected beat component. CONSTITUTION:A pilot signal generating circuit 3 is controlled by a control circuit 21 such as a microcomputer, and a pilot signal having a frequency not the same as a pilot signal recorded on a main track but a frequency different from fN or 3fN, that is, f2 or f4 is outputted at the frame reproduction. Thus, the pilot signal having the same frequency as that of the pilot signal recorded to any of adjacent track is outputted. Then the pilot signal is multiplied with the pilot signal included in the reproducing signal to detect its beat component and the stop position of a magnetic tape is detected from the detected beat component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a helical scan magnetic recording and reproducing device such as a video tape recorder.

[Summary of the invention]

In the present invention, an information signal and a tracking pilot signal are superimposed by a one-rotation head and recorded on a track inclined with respect to the longitudinal direction of a magnetic tape, and when the information signal is reproduced, a pilot signal is generated from a pilot signal generating means. In a helical scan magnetic recording/reproducing device that multiplies a pilot signal by a pilot signal included in a reproduced signal and detects the beat component for tracking control, the running of the magnetic tape is stopped and an information signal is generated by a rotating head. , the pilot signal generating means generates a pilot signal of the same frequency as the pilot signal recorded on one of the tracks adjacent to the main track being traced, and the pilot signal included in the reproduced signal is The beat component is detected by multiplication, and the stop position of the magnetic tape is detected from the detected beat component, making it possible to accurately detect the stop position of the magnetic tape even if the width of the rotating head is narrow. .

[Conventional technology]

In a helical scan magnetic recording and reproducing device, typified by a video tape recorder, in addition to normal playback, which plays back information signals recorded by running a magnetic tape at a predetermined speed, there are other functions such as still playback and frame-by-frame playback. In some cases, special playback is performed in which the running of the magnetic tape is stopped and information signals are continuously played back from one predetermined main track.

FIG. 3 is a block diagram of a portion for such special reproduction in a conventional helical scan magnetic recording and reproducing apparatus.

In the figure, reference numeral 1 denotes a low-pass filter, which separates and extracts a tracking pilot signal recorded superimposed on a television video signal from a reproduced signal from a rotating head (not shown) and passes it through. A multiplication circuit 2 multiplies the output of the low-pass filter 1 by the pilot signal outputted by the pilot signal generation circuit 3 in synchronization with the edge of a switching pulse (swp) for switching the head.

4 and 5 are band-pass filters, which extract components of frequency f, and frequency 3f from the output of the multiplier circuit 2, respectively, and output them to the detector 6.7 (f- is horizontal sync signal frequency). A differential amplifier 8 outputs the difference between the outputs of the detectors 6 and 7, that is, a tracking error signal.A comparator circuit 69 compares the output of the differential amplifier 8 and the reference potential output from the reference potential generation circuit 10. Compare the
The result is output to the detection circuit 11.

During normal playback, the magnetic tape is run at the normal playback speed,
A reproduced signal from the rotating head is supplied to a low pass filter 1. A low-pass filter 1 extracts a tracking pilot signal f from the reproduced signal.

to f4 are extracted and supplied to the multiplication circuit 2. Here, the frequency of each pilot signal fi to f4 is, for example, 6.5f
++, 7.5f layer, 10.5f, and 9°5f, respectively. On the other hand, the pilot signal generation circuit 3 sequentially outputs pilot signals of frequencies f to f4 for each field in synchronization with the switching pulse. As a result, the multiplication circuit 2 multiplies the pilot signal included in the reproduced signal (the pilot signal reproduced from the main track and the adjacent track) by the pilot signal input from the pilot signal generation circuit 3, and The components are output. Then, from the output of the multiplier circuit 2, the frequencies f and l are
and 3fI components are each extracted by a bandpass filter 4.5, rectified and smoothed by a detector 6.7, and converted to a DC level, and then the level difference between the two is outputted from a differential amplifier 8 as a tracking error signal. Ru. For example, the rotation of a capstan (not shown) is controlled in response to this tracking error signal.

On the other hand, for example, during frame-by-frame playback, the magnetic tape is temporarily stopped,
As shown in Fig. 4, if the main track on which the pilot signal of frequency f is recorded is traced by a rotating head, two rotations of the same azimuth are caused by a switching pulse as shown in Fig. 5(a). Head A, B
' are switched alternately, and R as shown in FIG. 5(b)
An F-fold signal envelope is obtained (where rotating head B
'' is mainly used in conjunction with rotary head A during still image reproduction, etc., and is provided corresponding to rotary head B having a different azimuth from rotary head A, which is used together with rotary head A during normal reproduction). At this time, the pilot signal generation circuit 3 generates frequencies f2 and f of the pilot signals recorded on the track 1 adjacent to the main track.
A pilot signal with a frequency f and 3f different from that of 4, that is, a pilot signal with a frequency f is fixed and output. In other words, the same pilot signal as the pilot signal recorded on the main track is continuously output. As a result, the output from the differential amplifier 8 is as shown in FIG. 5(c).
A tracking error signal as shown in is output. This tracking error signal is compared with a reference potential (zero potential) generated by a reference potential generation circuit 10, and the comparator circuit 9 outputs a positive signal when it is larger than the reference potential, and a negative signal when it is smaller than the reference potential, as shown in FIG. 5(e). Outputs comparison signal. The RF multiplied signal level reaches its peak (maximum or minimum) when the tracking error signal becomes zero. Therefore, the stop position of the magnetic tape can be detected by detecting, for example, the phase difference between the rising edge of the switching pulse and the rising edge of the comparison signal in the detection circuit 11.

[Problems solved by the invention]

However, such conventional devices are designed to obtain the same tracking error signal during special playback as during normal playback, so the width of the rotating head is narrow,
Alternatively, if there is a difference in the recording density characteristics of the magnetic tapes and there is little crosstalk from adjacent tracks, there is a drawback that it is difficult to accurately detect the stop position of the magnetic tape.

[Means for solving problems]

FIG. 1 shows a block diagram of a helical scan magnetic recording and reproducing apparatus of the present invention. In the figure, the same reference numerals are given to the parts corresponding to those in FIG. , during frame-by-frame playback, the pilot signal is not the same frequency as the pilot signal recorded on the main track, but has a frequency different by fl or 3f-,
That is, a pilot signal of frequency f2 or f4 is output. In other words, a pilot signal having the same frequency as the pilot signal recorded on one of the adjacent tracks is output. The other configurations are basically the same as those in FIG. 3.

[Effect]

The operation will be explained with reference to FIG.

During normal reproduction, the control device 21 causes the pilot signal generation circuit 3 to output a pilot signal of frequencies f to f in synchronization with the edge timing of the head switching pulse. Therefore, tracking control is performed using the tracking error signal output from the differential amplifier 8 in the same manner as in FIG.

Next, during frame-by-frame playback, the magnetic tape is temporarily stopped at a predetermined position, and a pilot signal with a frequency fl or 3f different from the pilot signal recorded on the main track is generated from the pilot signal generation circuit 3. Output. For example, as shown in FIG. 4, when the rotary head traces a main track on which frequency f1 is recorded, a pilot signal of frequency f, (or f4) is output. Since the frequencies of the pilot signal included in the reproduced signal from the rotating head are f□, f2, f4, the frequencies of the beat components are f, -f (= fl), f2
-f2 (=0), f4-f2 ("2fw), the band pass filter 4.5 passes the frequency fl
Since there are only signals of I or 3f, only the beat components of f and -f are extracted by the bandpass filter 4, detected by the detection circuit 6, and input to the non-inverting terminal of the differential amplifier 8. Because the input to the inverting terminal is zero.

The output of the differential amplifier 8 is as shown in FIG. 2 (Q).

That is, when the two rotary heads A and B' are alternately switched by the head switching pulse as shown in FIG. 2(,), the envelope of the reproduced RF signal is as shown in FIG.
As shown in b), when the rotary head A whose azimuth matches the main track is located approximately at the center of the magnetic tape (when the trace locus of the rotary head A has the largest overlap with the main track), the maximum , and decreases slightly when located at both ends. This also applies when the rotating head B' traces since the azimuths are the same. On the other hand, the levels of the beat components at frequencies f and -f change in accordance with the level of the pilot signal at frequency f1 in the reproduced signal, and the pilot signal is reproduced regardless of the azimuth, so the rotating heads A and B' When the overlap of the trace locus with the main track becomes the largest, the level of the beat component of frequency f, -fi becomes maximum.

In other words, the position of the maximum value (peak value) of this beat component corresponds to the position of the peak value (maximum value or minimum value) of the RF multiplied signal envelope.

Therefore, if the reference potential outputted by the reference potential generation circuit 10 is set to a value slightly smaller than the peak value of the output of the differential amplifier 8, the peak detection pulse as shown in FIG. can be obtained. If the pilot signal generating circuit 3 generates a pilot signal of frequency f4, a signal that is an inversion of the signal shown in Fig. 2(c) will be obtained, so in this case, the negative peak value should be detected. Just do it. The detection circuit 11 finds the center of this pulse and determines the head switching pulse.

By determining the phase difference from, for example, the rising edge of the signal, the position of the RF multiplied signal peak value can be detected. The center or phase difference of such a pulse can be easily calculated by counting a predetermined clock.

The detection signal of the RF multiplied signal peak value thus obtained is used as follows. In other words, frame-by-frame playback is performed by once stopping the magnetic tape, playing back a still image on one main track, then moving the magnetic tape slightly and playing back a still image on the next main track. However, if the stop position of the magnetic tape during still image reproduction is correct, the overlap between the portion traced by the rotary head A (B') and the main track is the largest. In other words, as shown in FIG. 4, the area where the trace locus of the rotary head A and the main track overlap (the shaded area in the figure) is the largest. In this case, the RF multiplied signal level is the highest and there is little noise appearing on the screen.On the other hand, if the stop position of the magnetic tape shifts, the trace locus of rotating head A (B'') overlaps the main track. The area (shaded area in the figure) becomes smaller, the RF multiplied signal level becomes smaller, and the noise that appears on one screen increases.This shift in the stop position of the magnetic tape is caused by the shift in the position of the RF multiplied signal peak value. In other words, if the stop position of the magnetic tape is correct, the RF multiplied signal peak value corresponds to the rotating head A (
B') occurs when it is approximately at the center of the main track (and therefore approximately at the center of the head switching pulse), but if the stop position shifts, the position at which the peak value occurs will shift toward the bottom or top of the magnetic tape. It will shift.

When the still image playback of one screen is finished and a frame-by-frame advance command is issued so that the next screen is played as a still image,
By changing the amount of movement of the magnetic tape in accordance with the detected deviation, the deviation is reduced in the next main track.

If the pilot signal output from the pilot signal generating circuit 3 and the pilot signal recorded on the main track are immediately matched when the magnetic tape is transferred from a stopped state to a running state during such special playback, the differential amplifier The signal output from 8 can be supplied to a tracking servo circuit (not shown) as a phase servo signal. However, in a state where matching cannot be achieved, if the signal output from the differential amplifier 8 is supplied as is to the tracking servo circuit, the tracking state will be disturbed. Therefore, during special playback, for example, only the so-called frequency servo is performed, which compares the output of a frequency generator that rotates in conjunction with the capstan with a predetermined reference value, and controls the rotation of the capstan in response to the error signal. You can do it like this.

In the above, the RF multiplied signal peak value is detected by comparing the output of the differential amplifier 8 with a fixed reference potential, but the reference potential is an average value signal obtained by rectifying and smoothing the output of the differential amplifier 8. You can also do that. In this way, even if the DC level of the output of the differential amplifier 8 changes, the reference potential also changes to follow the change, making the detection operation stable.

It is also possible to sample and hold the output of the differential amplifier 8 using clocks at predetermined short intervals, and detect the largest hold value as the peak value. Furthermore, the input and output of the sample and hold circuit may be compared by the comparator circuit 9. In this case, it is necessary to detect whether the slope of the output of the differential amplifier 8 is positive or negative, that is, the polarity, and the polarity is reversed at the peak value. , it is possible to obtain a pulse with a rising edge at the RF multiplied signal peak value. Alternatively, for example, the output of the differential amplifier 8 may be A/D converted to digitally detect the peak value.

〔effect〕

As described above, in the present invention, an information signal and a tracking pilot signal are superimposed by a rotating head and recorded on a track inclined with respect to the longitudinal direction of a magnetic tape.
When reproducing an information signal, a helical scan magnetic recording and reproducing device multiplies a pilot signal generated from a pilot signal generating means by a pilot signal included in the reproduced signal, detects the beat component, and performs tracking control. When the tape is stopped running and the information signal is reproduced by the rotary head, the pilot signal generating means is supplied with a pilot signal having the same frequency as the pilot signal recorded on one of the tracks adjacent to the main track being traced. The beat component is detected by multiplying it by the pilot signal included in the playback signal, and the stop position of the magnetic tape is detected from the detected beat component. Even when there is little crosstalk from adjacent tracks due to differences in recording density characteristics, it is possible to accurately detect the stop position of the magnetic tape.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the helical scan magnetic recording/reproducing apparatus of the present invention, Fig. 2 is its timing chart, Fig. 3 is a block diagram of a conventional helical scan magnetic recording/reproducing apparatus, and Fig. 4 is during frame-by-frame playback. A schematic plan view showing the track and the trace locus of the rotary head in FIG.
The figure is a timing chart. 1...Low pass filter 2...Multiplication circuit 3...
・Pilot signal generation circuit 4.5...Band pass filter 6.7...Detector 8...Differential amplifier 9...Comparison circuit 10...Reference potential generation circuit 11...Detection circuit 12 ...Control device P Fig. 2 (e) Mouth] 1 block I "L!I3@WP Fig. 4

Claims (1)

[Claims] When an information signal and a tracking pilot signal are superimposed by a rotating head and recorded on a track inclined with respect to the longitudinal direction of a magnetic tape, and when the information signal is reproduced, a pilot signal from a pilot signal generating means is used. In a helical scan magnetic recording and reproducing device that multiplies the generated pilot signal and the pilot signal included in the reproduced signal, detects the beat component, and performs tracking control, the traveling of the magnetic tape is stopped and the rotation is stopped. When reproducing the information signal by the head, the pilot signal generating means includes:
A pilot signal having the same frequency as the pilot signal recorded on one of the tracks adjacent to the main track being traced is generated, and the beat component is multiplied by the pilot signal included in the reproduced signal. What is claimed is: 1. A helical scan magnetic recording and reproducing apparatus characterized in that a stop position of the magnetic tape is detected from the detected beat component.