JP2629959B2 - Video tape recorder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermittent frame recording type video tape recorder suitable for long-time recording.

[Summary of the Invention]

The present invention relates to a video tape recorder of an intermittent frame recording type, in which a response characteristic of a servo control means of a rotating drum is switched for a predetermined short period immediately before the start of an intermittent transfer of a magnetic tape, so that a rotational magnetic field caused by the intermittent transfer of the magnetic tape is changed. By shortening the convergence period of the jitter of the head, the rotation of the magnetic head during frame recording is stabilized quickly, and skew distortion of the reproduced image when the recording interval is short is prevented.

[Conventional technology]

Conventionally, as a video tape recorder (VTR) for long-term recording for monitoring, etc., recording is performed with the tape stopped at the time of recording, the tape is sent at predetermined time intervals, and recorded again with the tape stopped. There is known an apparatus which repeats an intermittent recording operation (see Japanese Patent Application Laid-Open No. 63-133339).
At the time of reproduction, the screen is reviewed by continuously feeding the tape in the continuous reproduction mode, and if there is a notable screen, so-called frame advance is performed in the vicinity of the screen so that the screen can be inspected.

In this case, it is desired that the screen has no noticeable noise even in the continuous reproduction mode, that it is compatible with a general VTR, that the adjustment at the time of manufacturing is easy, and the like.

For this reason, the present applicant uses a pair of rotating magnetic heads (1A) and (1B) having a predetermined step h as shown in FIG. 3 and having different azimuth angles in Japanese Patent Application No. 62-204498. As shown in FIG. 4, a plurality of pilot signals are multiplexed with a video signal in a stationary state of the tape, and a plurality of pilot signals are recorded in a frame. According to the tracking detection signal, one of the magnetic heads scans the corresponding track to reproduce the video signal of one field, and during the period for the other field, the video signal of one field written in the memory is reproduced. By reading the data and compensating for the lack of the reproduced RF signal due to the difference in the trajectory of the magnetic head during recording and reproduction, a continuous reproduced image without noise is obtained even at the upper and lower edges of the screen. It has already proposed a long time video tape recorder for recording you.

[Problems to be solved by the invention]

However, in the conventional intermittent recording type VTR, at the time of recording, the tape that is intermittently driven causes disturbance to the rotating drum system, and changes the rotating speed of the drum. For this reason, if the temporal recording density is set high and the recording interval is set too short in order to increase the amount of information in the vicinity of the remarkable screen as described above, the magnetic head mounted on the drum and the tape The relative speed fluctuates even during the recording period of one frame, and the recording length of each horizontal cycle (H) of the inclined track on the tape fluctuates, thereby causing a problem that skew distortion occurs on the reproduction screen.

That is, in the conventional intermittent frame recording type VTR,
In synchronization with the switching pulse as shown in FIG. 5A,
For example, every eight frames, the capstan is driven intermittently based on a capstan drive control signal as shown in FIG.

At the time of the intermittent transfer, the magnetic tape comes into contact with the rotating magnetic head and the drum more strongly than at the time of the non-transfer, causing disturbance such as a band bleed, and the rotation of the magnetic head and the drum is reduced. For example, like 8mm VTR,
When the drum system is small and its coefficient of inertia is small, the rotation is remarkably decelerated.

In accordance with the fluctuation (jitter) of the rotation speed of the drum, an error voltage as shown in FIG.
Based on this error voltage, in the direction to eliminate the influence of disturbance,
The rotation of the drum is servo-controlled.

When the capstan drive control signal becomes “L ₀ ”, the magnetic tape enters a non-transfer state, the rotation of the drum gradually returns to a normal state, and the error voltage of the drum servo system gradually decreases.

There is no particular problem when the video signal is recorded intermittently in a state where the error voltage converges to a substantially constant value and the rotation of the drum is stabilized.

However, in order to shorten the recording interval in intermittent frame recording, during a period in which the error voltage of the drum servo system does not converge and the rotation of the drum is not yet stable, the recording is performed based on the REC enable signal as shown in FIG. 5E. When frame recording is performed, the rotational speed of the magnetic head during the frame period fluctuates, so that skew distortion occurs in the reproduced image as described above. Therefore, the minimum recording interval of the intermittent frame recording must be set longer than the convergence period of the jitter of the drum (and the head).

In view of the foregoing, an object of the present invention is to provide a video tape recorder that stabilizes the rotation of a magnetic head during intermittent frame recording quickly and prevents skew distortion of a reproduced image when a recording interval is short. There.

[Means for solving the problem]

The present invention provides a tape intermittent transfer means (40) for intermittently transferring a magnetic tape MT by a predetermined amount at predetermined time intervals, and a rotating magnetic head (1A), (1B) to a magnetic tape at the time of non-transfer. A video signal frame recording means (10) for recording a video signal in a frame, and a drum servo control means (20) for controlling rotation of a drum (2) equipped with a rotating magnetic head; In this video tape recorder, the response characteristic of the drum servo control means is switched within a predetermined short period of time to shorten the convergence period of the jitter of the rotary magnetic head caused by the intermittent transfer of the magnetic tape.

[Action]

According to the present invention, the rotation of the magnetic head during intermittent frame recording is fast and stable, and skew distortion of a reproduced image when the recording interval is short is prevented.

〔Example〕

Hereinafter, an embodiment of a video tape recorder according to the present invention will be described with reference to FIG. 1 and FIG.

 FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, a pair of magnetic heads (1A) and (1B)
Is mounted on the rotating drum (2). A magnetic tape MT is wound around the rotating drum (2) within a predetermined range, and is held between the capstan (4) and the pinch roller (5).

(10) is a video signal frame recording circuit, and a video signal from the TV camera CM is supplied to a recording signal processing circuit (11) via an input terminal (10i). The output of the recording signal processing circuit (11) is supplied to a recording amplifier (13) via a switch (12), and the output of the amplifier (13) is supplied to a magnetic head (1A) via a changeover switch (14). ) And (1B) are supplied alternately for each field. A control signal and a control signal are supplied from the timing control circuit (50) to the switches (12) and (14), respectively.

Reference numeral (20) denotes a drum servo system, which includes a phase servo circuit (21) and a speed servo circuit (22), and outputs from both servo circuits (21) and (22) are an adder (23) and a drive amplifier ( 24), is supplied to a drum motor (25) directly connected to the rotating drum (2). The output of a reference phase pulse generator (so-called PG) (26) is supplied to a phase servo circuit (21), and the output of a frequency pulse generator (so-called FG) is supplied to a speed servo circuit (22).

The reference oscillator (31) has two crystal oscillators (32) and (3
3) is selectively used by a switch (34), and the output of the oscillator (31) is divided into 1 / N by a frequency divider (35), and is outputted to a phase servo circuit (21) as a reference signal Sref. Supplied. The switch (34) is supplied with a control signal from the timing control circuit (50).

The oscillation frequency f ₃₂ of the one oscillator (32) is set equal to the example, the color subcarrier frequency f _SC, other oscillator (3
The oscillation frequency f ₃₃ of 3) is slightly larger than f _32, e.g.
1.02f Set to about _SC .

The intermittent capstan driving means (40) is configured so that the output of the capstan driving circuit (41) is supplied to the capstan motor (43) via the switch (42). The switch (42) is supplied with a control signal from the timing control circuit (50).

Next, the operation of the embodiment of FIG. 1 will be described with reference to FIG.

In the embodiment of FIG. 1, similarly to the conventional example, the capstan drive control signal as shown in FIG. B is synchronized with the switching pulse as shown in FIG. The capstan (4) is supplied intermittently by the control circuit (50) to the switch (42), and the magnetic tape MT is intermittently transferred.

Further, in this embodiment, immediately before the intermittent transfer of the magnetic tape MT, a frequency switching pulse as shown in FIG. 2C is supplied from the timing control circuit (50) to the switch (34). short "Hi", the oscillation frequency of the reference oscillator (31) is switched from f _SC for example 1.02f _SC. As a result, the output of the frequency divider (35), that is, the frequency of the reference signal Sref of the phase servo circuit (21) also increases by, for example, 2% during this short period.

Such a sudden increase in the frequency of the reference signal Sref changes the response characteristics of the drum servo system (20).

That is, when the frequency of the reference signal Sref is constant, the response characteristic of the drum servo system (20) to the disturbance due to the intermittent drive of the tape is as shown in FIG. 5D and as shown in FIG. It rises and falls relatively slowly according to the ON / OFF of the capstan drive control signal.

On the other hand, when the frequency of the reference signal Sref is switched, the error has changed suddenly, and the drum (2) cannot follow the instantaneous change.
Presents a transient response characteristic of a general secondary system, and the error signal immediately after the switching has a spike shape as shown in FIG. 2D.

Almost one field later than the frequency switching of the reference oscillator (31), the capstan drive control signal becomes “Hi”,
When the intermittent transfer of the magnetic tape MT is started, the rotation of the drum (2) is reduced as described above, and as shown in FIG. 2D, the error voltage of the drum servo system (20) becomes negative. Shake greatly.

In the case of this embodiment, the transient response characteristics of the drum servo system (20) include the frequency shift amount of the reference signal Sref, shift duration,
Although it changes according to the switching timing, it is set so that the error tends to gradually increase even after the capstan drive control signal is turned off.

The transient response characteristic is combined with the response characteristic as shown in FIG. 5D, and the gradual decrease tendency of the error after the control signal is turned off and the above-described gradual increase tendency are canceled out, as shown in FIG. 2D. And the error voltage reaches a negative maximum value within one frame after the start of the intermittent transfer of the tape, and thereafter converges relatively quickly. Then, during a period in which the error voltage converges and the rotation of the drum is stabilized, FIG.
By performing frame recording on the basis of the REC enable signal as shown in (1), a reproduced image without skew distortion can be obtained.

Instead of switching the frequency of the reference oscillator (31), the frequency division ratio of the frequency divider (35) may be changed as shown by the broken line in FIG.

In the above embodiment, the response characteristic of the drum servo system (20) is changed by shifting the frequency of the reference signal of the phase servo circuit (21) by a predetermined amount.

As shown by the broken line block in FIG. 1, a time delay circuit (51) and a high-pass filter (52) are provided as appropriate, and a control signal is supplied from a timing control circuit (50) common to both. Even when the switch (42) is controlled by the output of the delay circuit (50) and the output of the high-pass filter (52) is supplied to the speed servo circuit (22), the drum servo By appropriately changing the response characteristics of the system (20), the jitter of the rotating magnetic head can be quickly converged.

〔The invention's effect〕

As described above in detail, according to the present invention, the response characteristic of the servo control means of the rotary drum is switched for a predetermined short period immediately before the start of the intermittent transfer of the magnetic tape, and the rotating magnetic head caused by the intermittent transfer of the magnetic tape is switched. Video tape that can stabilize the rotation of the magnetic head for intermittent frame recording quickly and prevent the skew distortion of the reproduced image when the recording interval is short. A recorder is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of a video tape recorder according to the present invention, FIG. 2 is a time chart for explaining the operation of one embodiment of the present invention, and FIGS. 5 is a development view and a plan view for describing the invention, and FIG.
The figure is a time chart for explaining the present invention. (1A) and (1B) are magnetic heads, (2) is a rotating drum,
(4) is a capstan, (10) is a video signal frame recording means, (20) is a drum servo system, (31) is a reference oscillator,
(32) and (33) are crystal oscillators, (40) is a capstan intermittent driving means, and (50) is a timing control circuit.

Claims (1)

(57) [Claims] An intermittent tape transfer means for intermittently transferring a magnetic tape by a predetermined amount at predetermined time intervals, and a video signal frame for recording a video signal to the magnetic tape via a rotary magnetic head when the tape is not transferred. Recording means; and drum servo control means for controlling rotation of a drum on which the rotary magnetic head is mounted, and switching response characteristics of the drum servo control means for a predetermined short period immediately before the start of intermittent transfer of the magnetic tape. A video tape recorder characterized in that a convergence period of jitter of the rotary magnetic head caused by intermittent transfer of the magnetic tape is shortened.