JPH0342550B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video reproducing apparatus having four rotating magnetic heads and capable of obtaining reproduced images free of noise bands.

A two-rotation magnetic head type VTR that records video signals by forming recording tracks at a predetermined angle with respect to the longitudinal direction of the magnetic tape.A guard band is used between each track to increase the recording density of the magnetic tape. It is known that the azimuths of the magnetic gaps in the A and B heads are made to be different from each other in order to perform close recording in a state where there is no magnetic field and to minimize crosstalk from adjacent tracks during reproduction. When performing slow motion playback or still playback on such a VTR, the angle of the head scanning locus with respect to the recording track on the tape changes, and depending on the phase relationship between the track and the head, tracks with different recording azimuths may be traversed. Reproduction scanning is performed in a cut state (for example, a state in which the A head crosses the B track). When crossing tracks of different azimuths, the playback output is significantly reduced, resulting in band noise on the playback screen.

In order to correct this inconvenience, a head with the same azimuth as the A head is placed in substantially the same position as the B head.
A device with an A′ head has been proposed. In the case of slow playback, the magnetic tape is advanced intermittently,
Still playback and approximate standard speed playback are alternately repeated to obtain a slow motion screen at a predetermined playback speed. The tape stop position is controlled in synchronization with a control signal (hereinafter referred to as CTL signal) recorded on the side edge of the tape.
The head is stopped at a position where it can scan the A track. In still playback when the tape is stopped, the A track is scanned alternately by the A head and the A' head (field still). In addition, in approximate standard playback, the tape is driven by one CTL signal pitch (one frame) from the time when the A head starts scanning the A track in synchronization with the head rotational position detection pulse (hereinafter referred to as PG pulse). Ru. The period of this intermittent drive is approximately three field periods, during which the A head, B head, and A head sequentially scan the A track, B track, and A track. After that, field still is performed again using the A head and A' head.

In this way, reproduction as shown in ■■■ Tortoise Shell [0003] ■■■ is performed, and a slow motion image is obtained. Since each A head, A' head, and B head does not play back across tracks of different azimuths, no noise bands occur on the screen, and a high quality playback screen can be obtained.

However, in the slow playback method described above, except for one B head playback during approximate standard playback,
The disadvantage was that much of the information was lost due to the B head, resulting in slow motion images with unnatural movement.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to propose a video signal reproducing device that can obtain information approximately equally from A track and B track during slow motion reproduction to obtain a smooth slow motion image. That is.

The video signal reproducing apparatus according to the present invention includes a first pair of rotating heads having a first azimuth angle of about 180 degrees, and a second azimuth angle of the first pair of rotating heads provided close to each of the first rotating head pair. a second pair of rotating heads; a control signal head; and a first or second pair of rotating heads;
a circuit for forming drive pulses synchronized with the rotational phase of the rotating head of the rotary head; a capstan motor to which the drive pulses are supplied to feed the tape intermittently; a frequency generator associated with the capstan motor; means for generating a position signal indicating a corresponding tape position having a period approximately half the interval of control signals on the tape based on the timing at which a predetermined number of frequency signals are output from the control signal; and a circuit for forming a stop pulse for controlling the stop position of the tape based on the position signal. Each head is selected one after another to obtain a slow motion reproduction signal.

An embodiment of the present invention will be described below with reference to the drawings.

In this embodiment, the intermittent feed pitch of the tape during slow playback is set to 1 track pitch (that is, 1/2 CTL signal pitch), and in addition to the first pair of rotating heads (main heads) (A head and B head), 2 pairs of rotating heads (auxiliary heads) (A' head and
B′ head) is provided.

FIG. 1 is a schematic plan view of the rotary head drum of the VTR of this embodiment, and FIGS. 2 and 3 are front views of a double gearp head provided on the rotary head drum, respectively.

As shown in FIG. 1, the rotating head drum 1 has
Auxiliary A' and B' magnetic heads are provided adjacent to the main A and B magnetic heads, respectively, spaced apart by 180°. As shown in FIGS. 2 and 3, the A head and A' head have gaps 2a and 2a' with the same azimuth, and the B head and B' head have gaps 2b and 2b' with the same azimuth. are doing. The A head and the B' head constitute an integrated double gap head 3, and the A' head and the B head constitute a double gap head 4. The interval between each gap may be an integral multiple H in terms of the horizontal scanning period H.

FIG. 4 is a tape pattern diagram showing tracks on the magnetic tape 5 and head scanning trajectories. Fourth
As shown in the figure, tape 5 has tracks T _A and T _B.
are recorded alternately in opposite azimuths and close to each other. Control signals CTL are recorded on the control tracks at the side edges of the tape 5 at intervals of two track pitches (one frame).
The reproduced CTL signal is substantially representative of the position of A track T _A. The tape 5 is fed intermittently one track pitch at a time, and during the tape movement section, the main magnetic heads A and B perform standard speed playback, and during the tape stop section, the A/A' head or B, which matches the recording azimuth of the track at the stop position, performs playback at a standard speed. /B' head performs field still playback.

FIG. 5 is a block circuit diagram of one embodiment of the present invention, and FIGS. 6 and 7 are time charts for explaining the operation of FIG. 5.

A head switching pulse RF-SW (30 Hz) shown in FIG. 6A is supplied to the terminal 11 in FIG. 5. This head switching pulse RF-SW is applied to the rotating head drum 1.
The high level section indicates the tape contact section of the B head and A' head, and the low level section indicates the tape contact section of the A head and A' head.
It shows the tape contact section of the B′ head. In each of these tape contact sections, as will be described later, head switching between the A, A' heads and the B, B' heads as shown in FIG. 6B is performed to obtain a slow motion reproduction signal.

The head switching pulse RF-SW is supplied to the mono-multivibrator 12, and a pulse c having a pulse width of approximately an odd field interval (or approximately an even field interval from its rising edge) as shown in FIG. 6C is obtained. It will be done. By changing the pulse width of this pulse c, the slow motion speed can be adjusted.

The output of the mono-multivibrator 12 is further supplied to another mono-multivibrator 13, and the output pulse of the preceding mono-multivibrator 12 is supplied with a predetermined pulse width from the falling edge of the head switching pulse RF-SW as shown in FIG. 6D. An intermittent drive pulse d having a period determined by the width is formed. This intermittent drive pulse d is supplied to the motor drive circuit 14, and the output of this drive circuit 14 drives the capstan motor 1.
5 is driven intermittently. As a result, the B head (B track regeneration) or the A' head (A track regeneration)
The tape is advanced intermittently after scanning is completed. The duty of the intermittent feed is changed by changing the time constant of the mono-multivibrator 12 in the preceding stage,
This changes the slow speed ratio. In the example shown in FIG. 6D, the intermittent drive pulse d is formed every 4 fields, and the tape is
Since it is moved by a track pitch (= 1 field), a 1/4 slow image is obtained. Note that the tape may be moved after the scanning of the A head or B' head is completed.

In the section where the tape 15 is being driven, Fig. 6E
A playback control signal CTL shown in is obtained.
This playback control signal CTL is transmitted from track T _B in the tape movement section M shown in FIG. 6C.
Obtained by regenerating only when moving to T _A. The playback control signal CTL represents the position of the A track.

24 is a hold capacitor (capacitance is C) constituting a hold circuit, one end of which is grounded.
The negative pole of the DC power supply 26 is grounded, and its positive pole (from which a reference voltage <clamp voltage> E _C is obtained) is connected to the other end of the capacitor 24 via the on/off switch 21 . Constant current source (constant current is i ₀ ) 25
The negative terminal of the capacitor 24 is grounded, and the positive terminal thereof is connected to the other end of the capacitor 24 via the on/off switch 22. Further, an on/off switch 23 is connected in parallel to both ends of the capacitor 24.

27 is a magnetic head that reproduces the control signal from the tape, and the reproduced control signal
CTL (see FIG. 7C) is amplified by an amplifier 28 and supplied to the switch 21 from an input terminal 29 as a switching control signal. The switch 21 is turned on for a short period when the control signal CTL is "1", and turned off when it is "0".

17 is a frequency generator provided in relation to the motor 15. This generator 17 consists of a magnetic disc (N, S, N,
(for example, 90 N and S poles each) 18, and a pair of flux-responsive fixed magnetic heads 19A, 19B facing the circumferential surface of the magnet disk 18.
It consists of The distance between the magnetic heads 19A and 19B is such that the phase difference between the reproduction frequency signals FG _A and FG _B is
The angle is selected to be 90°. That is, if the distance between the magnetic heads 19A and 19B is Lh, and the pitch of the magnetic poles N and S is Lm, then Lh=(n+4/1)Lm.

However, n is n=0, 1, 2, . . . . this is,
These frequency signals FG _A and FG _B are transferred to the frequency multiplier circuit 20.
This is to obtain a frequency signal 8FG (see FIG. 7B) which is multiplied by 8. This frequency signal 8FG
is output in the same way whether the motor 15 rotates normally or starts. Note that the multiplication ratio of this frequency multiplication circuit 20 is arbitrary. The spacing between the magnetic heads 19A and 19B may be selected depending on the multiplication ratio. Moreover, this circuit 20 can also be omitted.

Further, the frequency signal 8FG from the multiplier circuit 20 is supplied to the switch 22 as a switching control signal. This switch 22 has a frequency signal 8FG of "1".
It is on for a very short period of time, and is off when it is "0".

A midpoint between the switches 21, 22 and the capacitor 24 is connected via a buffer amplifier 31 to an output terminal 37 from which a position signal {terminal voltage of the capacitor 24} E _P (FIG. 7A) is obtained.

32 and 35 are comparators, each of which has its non-inverting input terminal supplied with the above-mentioned position signal E _P , and whose respective inverting input terminal is supplied with each reference voltage E _S , E _B ( (see FIG. 7A).
Then, the first comparison output of the comparator 32 is supplied to a delay circuit 34 with a minute delay amount τ _r , and the obtained output is supplied to the switch 23 as a reset pulse RST (see FIG. 7D). This switch 23 is turned on for a short period when the reset pulse RST is "1", and turned off when it is "0".

Then, a brake start signal is output from the output terminal 38.
BS (see FIG. 7E) is obtained and supplied to the mono-multivibrator 16. In addition, FIG. 7F shows the tape speed, and NS shows the standard running speed. Then, a brake pulse f (see FIG. 6 F) is obtained from the mono-multivibrator 16 and is applied to the reverse input of the capstan motor 15 via the motor drive circuit 14, thereby applying an electromagnetic brake to the motor 15. be acted upon. Note that this brake pulse f is a signal that rises at the time when the brake start signal BS falls.

The time constant of the mono-multivibrator 16 determines the pulse width of the brake pulse f. In addition, by appropriately adjusting the position and pulse width of the brake pulse f, the tape 5 can always be positioned at a position where each magnetic head can scan the center of the A track or B track.
can be stopped. That is, as shown by still scanning trajectories S _A and S _B indicated by dotted lines in Fig. 4,
The tape is stopped at each track so that each head does not traverse tracks of different azimuth, thereby providing a slow playback screen without noise bands. In the tape stop section S shown in FIG. 6C, still playback is performed alternately by the A head and the A' head at the stop position of the A track.
At the next B track stop position, the B head and
Alternate still playback is performed by the B' head.
In addition, in the tape movement section M, the A, B heads or
Approximate standard playback is performed using heads A' and B'.

Next, the operation of the circuit shown in FIG. 5 will be explained. Now, assume that switches 21 and 23 are in the off state, and a frequency signal with a constant time width (≒25 μs)
When 8FG is input as a control signal to the switch 22, the terminal voltage of the capacitor 24 (position signal)
E _P increases by a constant voltage ΔE _P =i ₀ ·T ₅ /C every time one pulse of the frequency signal 8FG is generated. Therefore, the position signal E _P rises in a stepwise manner,
When the preset reference voltage E _S is exceeded, comparator 3
An output is obtained from switch 23, which is delayed by a minute time τ _r and then sent as a reset signal RST to switch 23.
is supplied, and this turns on. Thus, the capacitor 54 is reset and the position signal E _P becomes the ground potential (0V). The operating time of this reset loop is equal to the time τ _r if there is no delay from other circuit elements, and the value of the time γ _r is set sufficiently small (approximately 100 μs) compared to the pulse interval (approximately 1 ms) of the frequency signal 8FG. degree).

Capstan shaft controls tape
Since the machine is configured so that N pulses of the frequency signal 8FG are generated when the machine is moved by a distance equivalent to 1/2 pitch of CTL, the value of the reference voltage E _S is changed to (N-1)・ΔE _P If it is selected so that <E _S <N·ΔE _P , the terminal voltage E _P of the capacitor 54 becomes a staircase wave of N steps that is reset each time the tape moves by 1/2 pitch of the control signal CTL.

Meanwhile, the control signal from the moving tape
When the CTL is regenerated, the switch 21 is instantly turned on and clamps the position signal (staircase wave) E _P to a preset reference voltage (clamp voltage) E _C. Similar to the above-mentioned reset operation, this clamp operation is completed in a sufficiently short time with respect to the period of the frequency signal 8FG. In addition, the reference voltage (clamp voltage) E _C
shall not exceed the maximum value _ES of the staircase wave.

The position signal E _P (FIG. 7A) is obtained through the above processing, and by further comparing it with the variable reference voltage E _B using the comparator 35, the rising edge of the brake start signal BS is determined. In this case, the tape stops after traveling a certain braking distance from the braking start point (corresponding to ΔE _B ), so tracking control is performed by appropriately selecting voltage E _B with respect to voltage E _C.

Incidentally, slippage occurring between the capstan shaft and the tape is a problem, but as a result of investigation, this slip rate was approximately 0.1%. This error is eliminated by the clamp operation using the control signal CTL and will not accumulate, but even if the control signal CTL cannot be reproduced continuously over 20 to 30 steps, it will still occur in the position signal E _P. The error is estimated to be about one step of a staircase wave.

Strictly speaking, the value of the reference voltage (clamp voltage) E _C should be n・ΔE _P (n=0, 1, 2...N), but if N is sufficiently large and within 1 step of the staircase wave. Allowing for errors simplifies the configuration.
Also, tracking is done using reference voltage E _C and variable reference voltage.
Since it is determined only by the relative relationship of E _B , even if the voltage E _B is fixed and the voltage E _C is variable, the result is substantially the same as described above.

Thus, as shown in the time chart B in FIG.
A track and B track are respectively A head and B
Approximate standard speed playback is performed by the A' head or the A' head and the B' head, and during the tape stop period S, the A track is played back by the A head.
Still playback is performed in which tracks are played back alternately with the A' head, or tracks B are played back alternately with the B head and B' head.

According to this embodiment, since the reproduction ratio between the A track and the B track is 1:1, a slow motion reproduced image with smooth image movement can be obtained. Note that by changing the length of the tape stop period S, an arbitrary slow playback speed can be obtained.

According to the present invention described above, it is possible to obtain a video signal reproducing apparatus that does not generate noise bars on the screen during slow motion reproduction and can obtain information approximately equally from tracks having different recording azimuths.

Further, according to the present invention, the stop signal is generated at any point in the positive or negative range with respect to the timing of the control signal and its midpoint position, regardless of the lack of the control signal, and the tape is raised to an arbitrary target stop position. It is possible to obtain a video signal reproducing device that can stop the video signal with precision.

According to the present invention described above, based on the timing at which a predetermined number of frequency signals are output from the frequency generator associated with the capstan motor, the frequency signal has a period approximately half the interval of the control signals on the tape. ,
A position signal indicating the corresponding tape is generated, and a pulse indicating the tape stop position is formed based on this position signal, so even if some control signals are missing, the tape can be stopped reliably. Therefore, it is possible to reliably perform slow motion playback by intermittent feeding of the tape one track pitch at a time.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of a rotary head drum of a VTR to which the present invention is applied, FIGS. 2 and 3 are front views of a double gearp head provided in the rotary head drum of FIG. 1, and FIG. 5 is a tape pattern diagram showing recording tracks and head scanning trajectories on the magnetic tape, FIG. 5 is a block diagram showing an embodiment of the present invention, and FIGS. 6 and 7 show the operation of FIG. 5. It is a time chart. A and B are a first pair of rotating heads, A' and B' are a second pair of rotating heads, 15 is a capstan motor, and 17 is a frequency generator.

Claims (1)

[Claims] 1 A first pair of rotary heads having a first azimuth angle and spaced apart by approximately 180 degrees, and a second pair of rotary heads having a second azimuth angle provided in close proximity to each of the first pair of rotary heads. a control signal head; a circuit for forming drive pulses synchronized with the rotational phase of the first or second rotary head; a capstan motor to which the drive pulses are supplied to feed the tape intermittently; A frequency generator associated with the Pustan motor and a frequency generator having a period approximately half the interval of the control signal on the tape based on the timing at which a predetermined number of frequency signals are output from the frequency generator, and corresponding to the frequency generator. each comprising means for generating a position signal indicating the tape position, means for regulating the position signal by the control signal, and a circuit for forming a stop pulse for controlling the stop position of the tape based on the position signal, A video signal reproducing apparatus which obtains a slow motion reproduction signal by selecting each head of the first and second pair of rotary heads one after another while intermittently feeding the tape one track pitch at a time.