JPS5937785A - magnetic recording and playback device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for controlling frame advance playback and still playback in a magnetic recording/playback device such as a VT device.

In a conventional rotating head type helical scan VTR, a tape recorded at a standard specified tape speed is run at a different slow speed to play frame by frame, then the tape is stopped running and a still image is played back. Some functions are V
It is used in T-box.

When performing frame-advance still playback, the relative speed between the head and tape is different from that during recording during the frame-advance playback period when the tape is running at low speed, so the head plays back across video tracks. For this reason, the playback output from the head decreases during the period between tracks, and this 87N drop causes a so-called noise band on the playback screen, but the tape must be run at a position where this noise band does not appear on the playback screen. In order to stop and perform still playback, it is detected that the playback output from the head drops below a predetermined value (so-called dropout) during frame-by-frame playback, and this detection signal (dropout signal) Conventionally, it has been commonly used because it is simple to perform still playback with less noticeable noise by detecting that the video signal has arrived within or near the vertical blanking period and then stopping the tape running.

1 to 1, the playback output from the head is generally tape
There are random level fluctuations caused by unstable contact between heads and unstable head traces, making it difficult to stably detect dropout signals using the conventional method described above. In this case, the dropout signal is not detected, or even if it is detected, the dropout signal is detected over a wider period than necessary, making it impossible to control the transition from frame-by-frame playback to still playback. However, even if the playback is shifted to still playback, the noise reduction is insufficient and a noise band appears on the playback screen, making it impossible to obtain stable functional operation.

In view of the above, an object of the present invention is to provide a servo control device that realizes a stable frame-by-frame still playback function with a small-scale circuit in a magnetic recording and playback device that performs tracking control using a conventionally known four-frequency pilot signal. It's about doing.

The present invention provides an amplitude change in a difference frequency component obtained by frequency converting a pilot signal that is cyclically recorded and reproduced at four different frequencies based on a pilot signal that is cyclically generated at the same frequency at four frequencies. is detected, a pulse signal of a predetermined width is formed from the zero-crossing point of the detection signal, and the low-speed running of the tape is stopped when the pulse signal reaches the vicinity of the vertical blanking of the reproduced video signal. This allows frame-by-frame still playback.

EMBODIMENT OF THE INVENTION Hereinafter, the case where the present invention is applied to a rotary two-head type VTR will be explained in detail with reference to an embodiment thereof.

FIG. 1 is a diagram showing a tape pattern of a video track recorded by multiplexing a pilot signal and a video signal according to the present invention.

FIG. 2 is a diagram showing an embodiment of a servo control device for reproducing and controlling tracking.

In FIG. 1, tracks A and B are multiplexed with video signals and pilot signals by rotating magnetic heads 21 and 22 having different azimuth angles as shown in FIG. It is recorded and formed as follows.

The pilot signal f or f3 is on the track A.
In rack B, the pilot signal f or f4 is sequentially recorded cyclically for each track in the order of fl-'1fs, f, so that they correspond to each other. The frequency numbers of these pilot signals are determined, for example, as follows, where fH is the horizontal synchronization frequency of the video signal.

In FIG. 2, when normal playback is performed at standard speed, the switch 51 is connected to the terminal X side. -7'
1 is driven to run by a capstan motor 5. The rotating magnetic heads 24*22 are placed one above the other on the disk 2.
It is mounted at an angle of 800° and rotated together with the disk 2 by a disk motor. A magnet 38.degree. 3b is attached to the disk 2, which is detected by the tack head 13 to obtain pulses synchronized with the rotation of the magnetic heads 21, 22. The pulses from this tact head 13 are processed by a phase adjustment circuit 111.
After the phase is adjusted so that the magnetic head 2L22 and the magnetic tape 1 have a predetermined relative positional relationship, the pulse forming circuit 1
5. From this pulse forming circuit 15, a data ratio of 50% is synchronized with the rotation of the magnetic head 21, 22.
A pulse S is output.

Reference numeral 10 denotes a reference signal generation circuit which generates a reference signal having a frequency approximately equal to the frame frequency of the video signal. The phase comparison circuit 11 compares the phase of the pulse SC from the circuit 15 with the reference signal from the circuit 10, and the circuit 11 outputs a phase error signal that is equal to the phase difference between the two by one. This phase error signal is supplied to the disk motor 4 via the disk servo circuit 12, and as a result, the pulse S is servo-controlled to be phase-synchronized with the reference signal.
．． 22 is approximately the same frame frequency as when recording 1-
It rotates at a high rotation speed. The video signals and pilot signals that are alternately reproduced field by field from the magnetic tape 1 by the magnetic heads 21 and 22 whose rotation is controlled in this way are switched in the reproducing circuit 20 alternately for each field by the pulse S from the circuit 15. The reproduced video signal is outputted to the terminal 100, and the reproduced pilot signal P is supplied to the frequency conversion circuit 31.

Reference numeral 50 denotes a pilot signal generation circuit, which generates signals in response to pulses S from the circuit 15 during each field period in which the magnetic heads 21 and 22 alternately scan the magnetic tape 1 and during the period in which the magnetic head 21 scans the tape. , a local pilot signal f, or f3 is generated during the period when the magnetic head 22 scans the tape, a local pilot signal f2 or f4, and cyclically repeatedly generated in the order of fI + fl + fH + f4. This local pilot signal P, is supplied to the circuit 31.

The frequency conversion circuit 31 reproduces the pilot signal P from the circuit 20. is frequency-converted in accordance with the single-goal pilot signal P1 from the circuit 50, and the difference frequency component between the two is output from the FM53, and the tank circuit having resonance frequencies fH and 5FU, respectively, and its output are subjected to envelope detection. The signal is supplied to detection circuits 32 and 35 consisting of circuits such as

The output E from the detection circuit 32 is maximum when the difference frequency component of the 7JJ force from the circuit 31 is fH, and the output F from the detection circuit 33 is maximum when the difference frequency component from the circuit 51 is 3.
It is maximum at fH.

In FIG. 1, during the period in which the magnetic head 21 scans the track A3 on which the pilot signal f is recorded, the circuit 50 outputs the local pyro signal f. When the magnetic head 21 causes a tracking deviation from the scanning center of track A and deviates toward one adjacent track B3, a pilot signal P is output from the circuit 31.

The component f1~f,=fH increases as a difference frequency component between .

During the period in which the magnetic head 22 scans the next track B on which the pilot signal f is recorded, the circuit 50 outputs the local pilot signal f.

is output from the circuit 31, and when the track B is shifted from the scanning center to one adjacent track A4, the circuit 31 outputs f.
When the component of 27fB=3fa increases and shifts to the other adjacent block A, the component of f, to f,=fH increases.

In the amplifier circuit 34, in response to the pulse S of the circuit 15, during the period when the magnetic head 21 scans the tape, the difference between the 3fH# output from the circuit 33 and the fH acid component output from the circuit 62 ( 3fu-fa) is amplified and during the period when the magnetic head 22 scans the tape, the output fH acid component of the circuit 32 is of opposite polarity to that described above.
The difference (fH - 3fH) from the output sfH component of 3 is amplified, and the output G from this circuit 34 is passed through a low-pass filter 35 . Switch 51. It is supplied to the capstan motor 5 via the capstan servo circuit 60.

The control system configured by the above-described circuit allows the crosstalk components H and 5fH of the pilot signals detected from both adjacent tracks to be approximately equal for each track, that is, the scanning center of each track is scanned correctly. Page feedback is controlled and tracking is controlled.

Next, the operation of the servo control a (+ system) when performing frame-advance still playback according to the present invention will be explained using the waveform diagram in FIG.

In FIG. 2, when frame-by-frame still playback is to be performed, the switch 51 is switched to the terminal Y side.

The pilot signal generation circuit 50 cyclically generates pilot signals of four frequencies fI +fye and f4 in response to the pulse S from the circuit 15. In this embodiment, for example, r, , f4 , r, , In the chronological order of t4] During the period when the pulse S is at a high level (hereinafter abbreviated as 1H) and the magnetic head 21 scans the tape, f
l or f317) The pilot signal is also pulsed S
f or f during the period when the magnetic head 22 scans the tape at a low level (hereinafter abbreviated as 'L').
.

A pilot signal is cyclically and repeatedly generated and output.

40 is a phase shift circuit, 41 is a rectangular wave shaping circuit, and 42 is a pulse shaping circuit. 60 is a control circuit that controls low-speed running and stopping of the tape during frame-advance stealth playback;
Based on the manual input of the frame feed start command from 1, a capstan drive pulse W formed in synchronization with the pulse S from the circuit 15 is output and supplied to the capstan motor 5 via the switch 511 circuit 3o. , the motor 5 is pulse-driven and the tape 1 is run at low speed.

Further, as will be described later, the pulse J from the circuit 42 and the circuit 1
The phase of the pulse S from 5 is compared in this circuit 60, and when the two match, the capstan drive pulse W
output is stopped and tape running is stopped. Figure 1 shows an example of the scanning trajectory of the head during still playback.
61JA/. A broken line B' indicates the still scanning locus one track later.

FIG. 3 shows a waveform diagram of each part of FIG. 2 when these tracks A' and B' are scanned, PI shows the time series of the local pilot signal P from the circuit 50, and U shows the time series of the local pilot signal P from the head. The output waveform is shown, and N indicates the portion where the playback output level is minimum and observed as a noise band on the playback screen.

S indicates the waveform of the pulse S from the circuit 15, and as mentioned above, during the period when the pulse S is 1H', the head 21 is SS
In periods J and #, the head 22 scans the tape.

First, when the heads 21 and 22 scan over the tracks, they sequentially scan from the track A3 where the pilot signal f1 is recorded to the track B where the pilot signal f4 is recorded. Of the pilot signals (Po), the reproduction output level of the pilot signal f gradually decreases within the scanning period of the head, and the reproduction output level of the pilot signal f4 gradually increases. This regenerated pilot signal (Po) and the local pilot signal (P, ) from the circuit 50 are frequency-converted in the circuit 31, and the output difference frequency component is f, -f, = fH, or f4 to f, = fH, that is, the local pilot signal is f.

Alternatively, when c'xt, an output E having a waveform as shown in E in FIG. 3 is obtained from the circuit 32.

Also, a certain difference frequency component of the output light from the circuit 31 is f, N
When f4=sfut or f4~f,=3fH, that is, when the local pilot signal is f4 or f, an output F having a waveform as shown in F in FIG. 3 is obtained from the circuit 36.

In the circuit 34, as described above, the difference (B-F) or (F-E) between the output E from the circuit 32 and the output F from the circuit 33 is alternately switched in response to the pulse S from the circuit 15. (that is, the difference (F-E) is amplified during the period when the pulse S is 1H", and the difference (E-F) is amplified during the period when the pulse S is 1L".
) is amplified), so the output G from the circuit 34 is
As shown in Figure G, this results in a repetitive waveform with approximately continuous phase.

The repetition frequency is equal to 1/2 of the frequency of the pulse S, as is clear from the figure.

Also, from the same figure, the peak point Pl of the output G from the circuit 31 is located at the point N (that is, the noise band part) where the level of the reproduced output U from the head is the minimum, and the zero cross point Z8 of G is located at the peak point P of U. It is clear that it roughly corresponds to .

The output G of this circuit 34 is phase shifted by a phase shift circuit 40, and the zero cross point of the output H is 2. is the peak point P of G
It is characterized to correspond to l.

The output H of the circuit 40 is passed through the rectangular wave shaping circuit 41 to the FI
The square wave I is sufficiently amplified around the zero crossing point Z2 of
formatted and output.

An embodiment of this phase shift circuit 110 and rectangular waveform shaping circuit 41 is shown in FIG.

In FIG. 4, 401 is an input terminal for output q from circuit 34, 02 is an output terminal, and circuits 40 and 41 are both formed of differential amplifier circuits (or operational amplifier circuits).

The phase shift characteristic of the phase shift circuit dO is a resistor C, a capacitor C,
The phase shift circuit 40 has high-pass characteristics or band-pass characteristics for removing noise, unnecessary low frequency components, etc. contained in the output G from the circuit 54. It also operates as an amplifier circuit, and from the circuit 0, noise is removed and a stable desired output H is obtained. The circuit 41 operates as a so-called comparator, and its output I has a duty ratio of approximately 50%.
It becomes a rectangular wave, and its rising and falling edges are
This corresponds to the zero cross point z1 of the output H from the circuit 40.

The output I from the circuit 41 is supplied to a pulse shaping circuit 42, where a pulse J having a predetermined pulse width τ is formed and output at each rising and falling edge, as shown by J in FIG.

As is clear from the above description, the pulse J from this circuit 42 is output in correspondence with the point (noise band portion) N where the level of the head reproduction output U is minimum.

This relative relationship between pulses J and N is universal even if the head trace position changes, as is clear from the waveform diagram of each part in Figure 3 when scanning track B' in Figure 1. Therefore, it is easy to understand that the position of the noise band N can be indirectly detected using this pulse J.

On the other hand, during recording, the servo control system controls and records the vertical blanking portion of the video signal so that it is located in the vicinity of the rising and falling edges of the pulse S from the circuit 15. , in the circuit 60, the phase of the pulse When the edge phase of the pulse S arrives, it can be detected that the noise band N has arrived within or near the vertical blanking period of the reproduced video signal. Therefore, after detecting the phase of the pulse J, the capstan is driven. Stop the generation of pulse W,
By stopping the tape running, stable still playback can be performed with the noise band N being forced into or near the vertical blanking period, that is, with the noise band not appearing on the playback screen. In the conventional method of directly detecting the position of the noise band N from the playback output U from the head, it was difficult to stably detect it due to level fluctuations in the playback output U, but the method of the present invention described above According to
Since N can be detected stably, a stable and reliable frame-by-frame still playback function can be realized.

An embodiment of a control circuit 60 according to the present invention is shown in FIG. 61 is the input terminal for the frame feed start command, 62 is the circuit 4
63 is an input terminal for the pulse S from the circuit 15, and 64 is an output terminal for the capstan drive pulse W. 72 is a monostable multi-circuit, which is triggered by the rising edge of the pulse S from the terminal 63 and outputs a pulse of a predetermined width from the circuit 72. 7o is a D-type flip-flop, which has a pulse J from a terminal 62 inputted to the D input terminal and a terminal 63 inputted to the clock input terminal φ.
It has a function of comparing the phases of both pulses S from 7
1 is an AND gate. The flip-flop is reset by the frame feed star command from the terminal 61, its Q output becomes 'H', the AND gate 71 is opened, a pulse is output from the circuit 72, and the capstan drive pulse W is output from the terminal 64. The tape is output, and the tape is run at low speed and played frame by frame.

The phases of the pulse J from the terminal 62 and the pulse S from the terminal 63 are compared in the flip-flop 70, and if they match, that is, the pulse S rises within the period of the pulse width τ of the pulse J. When the phase arrives, the Q output of the 7rip 70g 70 becomes ``L'', the AND gate 71 closes, the output of the capstan drive nozzle W is stopped, tape running is stopped, and the still playback state is entered. According to the embodiment of the present invention shown in FIG. ) (Russ S
It is constantly compared and detected every cycle of /4 pulse J and pulse S.
Since the output of the capstan drive pulse W is not stopped as long as the phase match state of Even if it is detected by
Since it is ignored, it is possible to always ensure stable operation without being transferred to the still playback state at the imposed position. The embodiment shown in FIG.
However, the present invention is not limited to this; for example, even if the output of the capstan drive pulse W is stopped, the capstan motor 5 does not stop immediately and overruns. In such cases, or pulse J
If the phase is to be detected at a phase that is ahead of the phase of the noise band N, a signal that is detected ahead of the pulse S in time (for example, the output from the circuit 14) is used instead of the pulse S. Or, conversely, if the pulse J is detected at a phase that lags behind the phase of the noise band N, a signal (for example, the output from the circuit 10) whose timing is delayed from the pulse S is used. In general, it is sufficient to use a signal synchronized with the rotation of the G magnetic head 21 and 22. In either case, the effect obtained is the same and does not depart from the gist of the present invention. .

As described above, in the embodiment shown in FIG. 2, the quaternary pilot signal (Pt) is generated cyclically in the chronological order of fI gf2+f, , f in the circuit 50, but the present invention is not limited to this. The reverse chronological order f,,f3,f,
, f cyclically in the order, a similar effect can be obtained. In this case, FIG. 6 shows waveform diagrams of various parts in FIG. 2 when track B' in FIG. 1 is scanned. As is clear from comparing Figures 6 and 6 of the mouth,
The output E from the circuit 32 and the output F from the circuit name are different between FIG. 6 and FIG.
When local pilot signals are generated in the order of , f, , fl, when amplifying the difference between E and F in circuit 3, for example, if the difference (FE>) is always amplified, the output As shown in G in FIG. 6, it is clear that G has exactly the same waveform as G in the case of FIG.

In the embodiments shown in FIGS. 3 and 6 above, as &j10-cal pilot signal (P,), the pulse S is fl in the period of qH〃
Alternatively, the pilot signal of f3 is changed to f in the period of 'L'.
Alternatively, a pilot signal of f4 is generated, but conversely, a pilot signal of f or f4 is generated during the period of pulse S or H', and a pilot signal of fl or f3 is generated during the period of pulse 'L'. A similar effect can be obtained when generating fl ・f 2 ・ f
3 and f are generated in the order, and waveform diagrams of various parts in FIG. 2 are shown when track B' in FIG. 1 is scanned.

When local pilot signals are generated in the order of f, , f2, f3, f, as described in FIG. F-E) are amplified alternately, so that the output G reaches its zero crossing point Z r as shown in G in FIG.
corresponds to the noise band N. Therefore, in this case, this output G is directly connected to the circuit 41.
If the signal is supplied to the signal and shaped into a rectangular wave, its output will have the same timing relationship as 1 in FIG. 3 or 6, and therefore the same effect as described above can be obtained.

As described above, according to the present invention, conventionally known four
In a magnetic recording/playback device that performs tracking control using a frequency pilot signal, it is possible to achieve a stable frame-by-frame still playback function by using the pilot signal.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a track pattern on which pilot signals are recorded according to the present invention, FIG. 2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a waveform diagram of each part thereof, and FIG.
The figure is a circuit diagram showing an embodiment of a phase shifting circuit and a rectangular wave shaping circuit according to the present invention, FIG. 5 is a circuit diagram showing an embodiment of a control circuit according to the present invention, and FIGS. 6 and 7 are FIG. 7 is a waveform diagram of each part based on another embodiment of the present invention. 50; high lot signal generation circuit; 31; frequency conversion circuit; 32. 33; detection circuit; 34; amplifier circuit; 40; phase shift circuit; 1; rectangular wave shaping circuit; d2; pulse shaping circuit; 60; control circuit. 3rd 8th 4th-Kyou J

Claims (1)

[Claims] 1. Magnetic recording and playback in which a four-frequency pilot signal is multiplexed with a video signal and recorded on a magnetic tape using a rotating magnetic head in a predetermined time-series order, cyclically for each scanning period of the magnetic head, and then played back. In the apparatus, means for separating the pilot signal multiplexed therein from the reproduced video signal, and a chronological order that is the same as the chronological order of the four-frequency pilot signals generated during recording, or a chronological order that is the opposite thereof. a pilot signal generation circuit that cyclically generates a four-frequency pilot signal at a frequency, a frequency conversion circuit that converts the frequency of a regenerated pilot signal from the above means based on one pilot signal from the pilot signal generation circuit; a detection circuit that sequentially detects vibrational changes in the difference frequency component of the output from the conversion circuit every scanning period of the magnetic head;
It has a detection circuit that detects the zero-crossing point of the output from the above-mentioned detection circuit, or the zero-crossing point of the output obtained by shifting the phase of the output from the above-mentioned detection circuit via a phase shift circuit, and the magnetic tape is moved at low speed. 2. A magnetic recording and reproducing apparatus, characterized in that, after running the tape, the tape running is controlled to stop when the detection signal from the detection circuit reaches the vicinity of vertical blanking of the reproduced video signal.