JPS59151583A - Video tape recorder - Google Patents

Abstract

PURPOSE:To prevent generation of noise at switching of reproducing speed by selecting a running position informing signal having the fastest phase locking by means of a phase comparing means among running position informing signals proportional to n-times speed reproduced from a magnetic tape. CONSTITUTION:A signal obtained by a rotating phase detecting head 11 is inputted to a waveform processing circuit 12, where the signal is waveform-shaped. An output of the waveform processing circut 12 is inputted to a monostable multivibrator (MM) 13. An output signal of a timing circuit 35 is inputted to MMs 32 and 33. The output signal of the MM13 is inputted to the MM32 and the output of the MM32 is inputted further to the MM33 and the output signal of the MM33 is applied to a selecting circuit 31. A control signal reproduced when the output signal of the MM33 is logical high is selected by the selecting circuit 31 and an output signal (f) is obtained. The signal of the phase control circuit 17 and the output signal of a speed control circuit 23 are added at an adder 24 so that the leading of the signal (f) is made stable at the center of a slant of a trapezoidal wave.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a helical scan type video tape recorder C (hereinafter abbreviated as VTR), in which the playback speed is switched from normal playback to double speed playback, triple speed playback, etc. To provide a VTR in which phase control of a capstan motor can be quickly pulled in, and noise does not appear on a playback screen.

Conventional Structure and Problems In recent years, VTRs have been developed in the direction of diversification, miniaturization, and cost reduction. Among them, one of the multi-functionality is playback at a speed different from normal playback such as slow motion playback, fast forward one rewind playback, reverse playback, double speed playback, triple speed playback (hereinafter referred to as special playback). A VTR (referred to as VTR) has been developed and commercialized, and good images can be obtained because the period in which the reproduction output decreases is located near the vertical synchronization signal.

Hereinafter, a case in which conventional normal playback is switched to double speed playback will be explained with reference to the drawings.

FIG. 1 is a block diagram of a conventional capstan motor control section. 1 is a magnetic tape, which is driven by a capstan motor 2 and a pinch roller 3 in the direction indicated by the arrow. Rotary magnetic heads 6 and 6 mounted on rotary head par 4 rotate in the direction of arrow H to record and reproduce video signals on magnetic tape 1 guided by guide posts 7 and 8.

Detection of the rotational phases of the rotary magnetic heads 6 and 6 is obtained by a well-known method using a magnet 10 attached to the rotational drive unit 9Vc and a rotational phase detection head 11. The signal obtained by the rotational phase detection head 11 is input to a waveform processing circuit 12 and waveform-shaped.

The output of the waveform processing circuit 12 is output to a monostaple multivibrator. One terminal of a variable resistor 14 is connected to the MM13, and the other terminal of the variable resistor 14 is connected to the power supply terminal 1.
6. By varying the variable resistor 14, the delay width of the MM 13 can be changed. MM
The output signal of 13 is input to a phase control circuit 17 via a trapezoidal wave generator 16.

On the other hand, the control head 18 is connected to the magnetic f-plane during recording. The control signal recorded at one frame time interval is reproduced, and the reproduced control signal is amplified by an amplifier 19 and input to a frequency divider 20. Frequency divider 2
The output signal of the speed command 3o is input to the speed command 3o, and the division ratio thereof can be changed according to the speed command signal. The output signal of the frequency divider 20 is input to the phase control circuit 17.

The EG head 21 obtains a rotation speed signal having a frequency corresponding to the rotation speed of the capstan motor 2. The obtained signal is input to the speed control circuit 23 via the amplifier 22. Further, an output signal of a speed command 30 is input to the speed control circuit 23 . The speed control circuit 23 is configured to rotate the capstan motor 2 at a constant speed in response to a signal of the speed command 3o. The output signal of the speed control circuit 23 and the output signal of the phase control circuit 17 are added by an adder 24, and the speed and phase of the capstan motor 2 are controlled by the output signal.

The operation of the conventional VTR configured as described above when the playback speed is fully switched from normal playback to double speed playback will be described with reference to FIG. In FIG. 2, (a) shows the recording track number of a 2-head VTR (in which turns are arranged repeatedly, one scale on the horizontal axis indicates the time of one field,
At the same time, the timing of the homopolar magnetic head switching signal (hereinafter referred to as head SW signal f)' is also shown. Further, the vertical axis indicates the amount of movement of the shaft, and each scale indicates the amount by which the magnetic tape travels in one flotation time during dispensing or normal playback. At the same time, the one scale mark indicates the recording track width. The head gap angles of the two video heads are slightly different f), resulting in azimuth recording.

Therefore, in the recording trunk pattern shown in FIG. 2(a), the tracks recorded by one head are represented by odd numbers, and the tracks recorded by the other B head are represented by even numbers. Odd tracks are represented by A heads, and even tracks are represented by even numbers. It can only be played on the B head. The thick line in FIG. 2(a) represents the head trajectory when switching from normal playback to double speed playback.

(b) is the reproduction envelope waveform at that time. FIG. 2(0) shows the head S obtained by the waveform processing circuit 12 in FIG.
It is a W signal. FIG. 2(d) shows a switching signal between normal playback and double speed playback, which is an output signal of the speed command 30 shown in FIG. Since the speed command is switched by the user's operation, the timing is uncertain. Now, by chance, the head SW
Suppose that the speed is changed at the falling edge of the signal. Figure 2 (e
1) is a control signal reproduced by the control head 18, and this control signal is, for example, at the center of each frame (OoS) where the lower end of the head trajectory in FIG. 2(a) is the vertical axis.

1.5, 2, 5. ...) will be played when passing.

This control signal is divided by the frequency divider 20 to 1/1 for normal playback, 1/2 for double speed playback, 1/n for nx speed playback, and the edge waveform (f) of the signal is divided by 1. configured to be output.

FIG. 2(g) shows the output signal of the trapezoidal wave generating circuit 16 in FIG.
) starts at the falling edge of .

The signals shown in FIG. 2 (0 and (g)) are input to the phase control circuit 17, and the phase control circuit 17 controls the phase control signal so that the edge pulse of the signal (f) is stabilized at the center of the slope of the trapezoidal wave (g). The output signal is added to the output signal of the speed control circuit 23 to control the capstan motor 2.

Further, the variable resistor 14 is usually called a tracking volume, and by changing it by the user, the magnetic tape running phase can be changed so that the reproduced output signals of the rotary magnetic heads 5 and 6 can be adjusted to the maximum. This conventional VT
In configuration R, even if the playback output signals of the rotating magnetic heads 5 and 6 are adjusted to be maximum during normal playback and double-speed playback, when switching from normal playback to double-speed playback, double-speed playback will occur. Time playback control signal (6) I-divided control signal for each frame (when set to 0, depending on the relationship between the speed command switching timing and the control signal (e) and the configuration of the divider 20)
Therefore, it is uncertain whether the control signal marked 0 in FIG. 2(e) or the control signal marked X is selected. Even if the configuration is such that the control signal immediately after the speed changeover is selected, the results differ depending on whether the control signal is reproduced immediately before or after the speed changeover.

Therefore, after the double-speed playback starts, for example, if the control signal marked with an X is selected as shown in FIG. 2 (0), the phase control circuit 17 outputs a control signal assuming that the phase is significantly shifted b, and finally the head trajectory moves from the bold line trajectory in Fig. 2(a) to the broken line trajectory and becomes stable, and as shown in Fig. 2(a).
Obtain the same playback envelope as in b). The pull-in time is about 0.6 to 1 second, depending on the characteristics of the control circuit, and during this time a noise bar is generated on the playback screen, resulting in an extremely unsightly screen. This is true not only for double-speed playback but also for n-times playback, which has the problem of noise generation when switching playback speeds.

OBJECTS OF THE INVENTION An object of the present invention is to provide a VTR that does not generate noise even when switching playback speeds.Constitution of the InventionThe present invention has a rotating cylinder equipped with two rotating magnetic heads, a magnetic tape running means for fully driving the magnetic tape using a capstan motor and a pinch roller;
speed switching means for switching the running speed of the magnetic tape;
a reproducing means for reproducing a running position information signal recorded on the magnetic tape; a rotational phase detecting means for outputting a rotational phase signal of the rotary cylinder; and a running position information signal reproduced from the rotational phase signal and the magnetic tape. and a control means for controlling the capstan motor according to the output signal of the phase comparison means,
In the speed switching by the speed switching means, the speed is switched to n times speed in synchronization with the rotational phase of the rotary cylinder, and the speed is changed by the phase comparing means in the traveling position information signal proportional to n times reproduced from the magnetic tape. It is configured to select the traveling position information signal with the fastest phase pull-in, thereby making it possible to obtain a good reproduced image without generating noise when switching the reproduction speed.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a configuration diagram of a capstan motor control section in an embodiment of the present invention, and the same components as in FIG. 1 are numbered the same. Attached.

In FIG. 3, the magnetic tape 1 is connected to the capstan motor 2.
and travels in the direction of arrow F by the pinch rollers 3. The rotating magnetic heads 5 and 6 mounted on the rotating magnetic head par 4 rotate in the direction of arrow H, and record and reproduce video signals on the magnetic tape 1 guided by guide posts 7 and 8. Detection of the rotational phase of the rotary magnetic heads 6 and 6 is obtained by a well-known method using a magnet 1o attached to the rotary drive section 9 and a rotary phase detection head 11. The signal obtained by the rotational phase detection head 11 is input to a waveform processing circuit 12 and subjected to waveform shaping. The output of the waveform processing circuit 12 is manually input to the MM13. One terminal of a variable resistor 14 is connected to MM13, and the other terminal of the variable resistor 14 is connected to a power supply terminal 15. By varying this variable resistor 14, MML
The output signal of the OMM 13 whose delay width can be changed is inputted to the phase control circuit 17 via the trapezoidal wave generator 16.

On the other hand, the control head 18 is attached to the magnetic tape at the time of recording.
A control signal recorded at one frame time interval is reproduced, and this control signal is amplified by an amplifier 19 and inputted to a selection circuit 31. The output signal of the selection circuit 31 is input to the phase control circuit 17.

The FG head 21 detects the capstor motor 20 rotation speed signal. The detected signal is input to the speed control circuit 23VC via the amplifier 22. The timing circuit 35 receives the speed command 3o signal and the output signal of the waveform processing circuit 12, and
A speed command signal is output at a timing synchronized with the head S field signal.

The output signal of the timing circuit 35 is input to the speed control circuit 23. The speed control circuit 23 is the timing circuit 3
Speed command signal timed at 5? In response, the capstan motor 2 is configured to rotate at a constant speed.

On the other hand, the output signal 11 of the timing circuit 35 is input to MM32 and MM33. MMl 3 for MMa2
The output signal of MM32 is inputted, and the output of MM32 is further M,
The output signal of MM33 is input to the selection circuit 3.
1 is supplied.

In the embodiment of the present invention configured as described above, the operation when switching the playback speed from normal playback to double speed playback 'f: 4th
I will explain the 4th version. In Fig. 4 (-) shows a state in which the recording track pattern of a 2-head VTR is repeatedly arranged as in Fig. 2, and one scale on the horizontal axis indicates the time of 17 supers, and at the same time the timing of the head S field signal. Also, the vertical axis shows the amount of tape movement, and one scale indicates the total distance that the magnetic tape travels in one fold time during recording or normal playback.Similarly, one scale indicates the recording track. The thick line in FIG. 4 (+L) represents the head trajectory when switching from normal playback to double speed playback using the configuration of the present invention. (b) is the playback envelope waveform at that time. During double-speed playback, the time during which the playback envelope decreases is located near the switching point of the hend SW signal, that is, the vertical "U" synchronization signal, so the playback screen is good.

FIG. 4(0) shows the head S field signal obtained by the waveform processing circuit 12 of FIG. FIG. 4(d) shows a switching signal between normal playback and double speed playback, and is an output signal of the speed command 30 shown in FIG. Since the speed command is switched by the user's operation, the timing is uncertain. -, Fig. 4 (
k) is the output signal of the timing circuit 36 in FIG.
Speed command signal (d) input at any timing
rThe speed switching timing may be set so that the playback envelope after the speed switching is good.0 FIG. 3(e) shows the control signal reproduced by the control head 18, and this control signal is, for example, as shown in FIG. The lower end of the head trajectory in a) is at the center of each frame on the vertical axis (0, 6,
1, 5, 2, 6...)''f: f: The θ reproduced when
The slope of the trapezoidal wave in the output signal of MMl3 starts from the fall of the output signal Ql).

FIG. 4(i) ld is the output signal of MM32 in FIG. 3,
The start timing of waveform generation is determined by the output signal of MMl2 (
11) starts from the falling edge. e) is MM3 in Figure 3.
3, and the start timing of waveform generation begins at the falling edge of the output signal (i) of MM32.

Further, MM32 and MM33 are configured to change their delay widths according to the speed command due to the lack of the output signal of the timing circuit 36 which is the speed command signal. During double-speed playback, the delay width of MM32 is wide (and the delay width of MM33 is changed to be narrow. As a result, the center of the output signal (j) of MM33 and the center of the slope of the trapezoidal wave (g) are almost the same. The delay width is within the time interval of the playback control signal at each speed, that is, within 33.3 mS for normal playback and 16.6mS for double speed playback.
Set it so that it is within the range.

By inputting the output signal (li)'e of the MM33 to the selection circuit 31, the control signal reproduced during the High period of the output signal 0) of the MM33 is selected and sent to the selection circuit 3.
1 output signal (nff is obtained. Phase control circuit 17 in FIG.
The signals (0 and (g) in Fig. 4 are input to
The phase control circuit 1T outputs a phase control signal so that the phase control signal is stabilized at the center of the slope, and is added to the output signal of the speed control circuit 23 by an adder 24 to control the capstan motor 2.

As described above, according to this embodiment, the speed switching timing is set so that the playback envelope after switching is good, and the control signal for phase control is the most suitable for the trapezoidal wave for phase control. By adopting a configuration that selects proximate cause control signals, it is possible to prevent the head from moving to a different scanning trajectory due to the function of the phase control circuit even though the scanning trajectory of the head is almost good9. Of course, the present invention has the following advantages:
This is not limited to the above embodiment, but even at n-times speed, there is a function that selects all control signals closest to the slope of the trapezoidal wave that cannot be phase controlled, one per frame period. It is fine if you have it.

Effects of the Invention As is clear from the above explanation, the present invention switches the playback speed with timing so that the playback envelope after the speed change is good, and the control signal for the phase control is controlled so that the playback envelope after the speed change is good. By adopting a configuration that selects the control signal closest to the trapezoidal wave, even though the playback envelope after speed switching is good, the phase control circuit moves to a different scanning trajectory and noise is generated. This eliminates the occurrence of noise bars, and even if the playback speed is arbitrarily switched, a good image without noise bars can be obtained.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram of the capstan motor control section in a conventional VTR, and Figure 2 is an explanatory diagram of the operation when switching the playback speed from normal playback to double speed playback in the conventional example shown in Figure 1, and the main parts. FIG. 3 is a circuit configuration diagram of the capstan motor control section in an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the operation when the playback speed is switched from normal playback to double speed playback in the embodiment of the present invention shown in FIG. 3, and a waveform diagram of the main parts. 1・°゛“Magnetic tape, 2・°・°・capstan motor, 6.6...Rotating magnetic head, 12...
...Waveform processing circuit, 13, 32.33... Monostable multipipulator (MM), 14...
...Variable resistor, 16...Trapezoidal wave generator, 17
...Phase control circuit, 18...°°・Control head, 20°°°゛°゛Frequency divider, 21...F
C head, 23...speed control circuit, 3o...
...Speed command, 31...Selection circuit.

Claims (2)

[Claims] (1) A rotating cylinder equipped with at least two rotating magnetic heads, a magnetic tape running means for driving a magnetic tape using a capstan motor and a pinch roller, and a speed switching means for switching the running speed of the magnetic tape. , a reproduction means for reproducing a running position information signal recorded on the magnetic tape, a rotational phase detection means for outputting a rotational phase signal of the rotary cylinder, and a running position reproduced from the rotational phase signal and the magnetic tape. It comprises a phase comparison means for comparing the phases of information signals, and a control means for controlling the capstan motor according to the output signal of the phase comparison means, and the speed switching by the speed switching means is controlled according to the rotational phase of the rotary cylinder. The speed is switched to n times speed in synchronization, and the traveling position information signal whose phase is the earliest to be drawn in by the phase comparison means is selected from among the traveling position information signals proportional to n times reproduced from the magnetic tape. A videotape recorder characterized by: (2) The phase comparison means includes a delay means for delaying the rotational phase signal of the rotary cylinder by a predetermined width, and a signal processing means for obtaining a trapezoidal wave signal from the output signal after the delay by the predetermined width. 2. The video tape recorder according to claim 1, wherein information signals are selected such that the traveling position information signal closest to the slope of the trapezoidal wave signal is selected.