JPH0832018B2 - Helical scan type magnetic reproducing device - Google Patents

Description

The present invention relates to a helical scan type magnetic reproducing apparatus.

[Prior Art] In a conventional helical scan type magnetic reproducing apparatus in which a plurality of magnetic heads are arranged on a rotating drum, reproducing video signals from a plurality of magnetic heads, for example, two magnetic heads, are rotated by a rotating position of the rotating drum. According to the above, the reproduction was performed by alternately switching each field. This switching is called head switching. By winding a video tape around a rotating drum by 180 ° or more, the video signals from two consecutive tracks are overlapped and played back, and this is detected and the rotating position of the rotating drum is detected. ing. This switching was done while playing the lower part of the screen to make it inconspicuous.

[Problems to be Solved by the Invention] However, due to the fact that the tension of the video tape is different between recording and reproduction, skew distortion on the reproduction screen, that is, reproduction from the point where head switching is performed (switching point) is reproduced on the screen. There are problems that the horizontal position of the image of the object deviates from it and that the switching point moves accordingly when tracking adjustment is performed.As a result of the recent improvement of TV and video monitor, However, since various adjustments have been made to the television and the like so that the lower part of the screen can be seen, there is a problem that noise on the screen due to the head switching becomes noticeable. For example, the switching point is usually set at 6.5H (horizontal scanning period) before the vertical sync signal, but about ± H
There was a 3H shift. Therefore, the switching position appears on the screen from 8H to 4.5H immediately before vertical synchronization.
The place where head switching was done was entering the screen.

Also, when playing back a video tape recorded by another VTR, the switching point may shift during playback depending on where the video signal was recorded in the width direction of the tape, and it may come into the screen more. There was a point.

The present invention provides a helical scan type magnetic reproducing apparatus that performs head switching at a fixed position (timing) on a screen without being affected by changes in the tension of the video tape and tracking adjustment when reproducing the video tape. It is an object.

[Means and Actions for Solving the Problems] In order to achieve the above object, the present invention provides a helical scan type magnetic reproducing apparatus in which a magnetic field for switching video signals reproduced by a plurality of magnetic heads is used. The switching is performed by reading the position signal stored after the first predetermined time elapses and further stored after the second predetermined time elapses in response to the vertical synchronizing signal of the reproduced video signal of the position signal from the head position detecting means. A switching signal generating circuit is provided.

As a result, head switching is performed at a fixed timing with respect to the reproduced video signal, so that it is possible to provide a helical scan type magnetic reproducing device capable of fixing the position of the switching point appearing on the screen. It was

That is, a plurality of magnetic heads, position signal generating means for generating position signals representing the positions of the plurality of magnetic heads, and a video signal reproduced by the plurality of magnetic heads are responsive to the position signals from the position signal generating means. In a helical scan type magnetic reproducing apparatus having a switching means for switching in accordance with the above, a first position signal is stored in response to a vertical synchronizing signal of the video signal after a lapse of a first predetermined time from the reception of the vertical synchronizing signal. Means for responding to the vertical synchronization signal and first after receiving the vertical synchronization signal
And a second means for reading and outputting the position signal stored in the first means after a second predetermined time, which is longer than the predetermined time, is provided.

[Examples] Examples will be described with reference to the drawings. FIG. 1 shows the first and second helical scan type magnetic reproducing apparatus of the present invention.
3 is a block diagram of a head switching circuit of the embodiment of FIG.

In FIG. 1, reproduced signals from a video tape (not shown) are respectively input to and amplified by amplifiers 2a and 2b by two magnetic heads 1a and 1b arranged to face a rotary drum (not shown) by 180 °. The outputs of the amplifiers 2a and 2b are input to the switch S1. The switch S1 has two magnetic heads 1a,
The reproduction signal from 1b is switched in response to the switching signal 107. As a result, the signal from the magnetic head 1a or 1b in contact with the video tape is sent to the video signal processing circuit 3. The video signal processing circuit 3 generates a reproduced video signal of the NTSC system or the like and sends a reproduction synchronization signal 101 to the switching signal generation circuit 4. A signal indicating the position of the magnetic head, that is, the rotational position of the rotary drum is further input to the switching signal generation circuit 4. This signal is the magnetic head position signal 105, which is a signal that switches when the magnetic heads 1a and 1b reach a predetermined position, and is also called a drum flip-flop. The switching signal generation circuit 4 uses this magnetic head position signal.
105 is stored after the first predetermined time has elapsed after receiving the reproduction synchronization signal 101, and which one of the magnetic heads should reproduce the signal, and then the second predetermined time has elapsed after the reception of the reproduction synchronization signal 101. The magnetic head position signal 105 stored later is output. This output, that is, the switching signal 107 switches the switch S1. The second predetermined time is set to be shorter than the cycle of the vertical synchronizing signal by 3H (horizontal scanning period). Therefore, the switching timing of the switch S1, that is, the switching point is 3H relative to the timing of the reproduced video signal.
It will be fixed before and will also be fixed on the playback screen. The rotation of a rotating drum (not shown) is controlled by the magnetic head position signal 105. In this way, the magnetic head position signal 10
Even if the phase between 5 and the playback video signal changes, the switch S1 is switched at the predetermined switching point for the playback video signal.
It became possible to switch. Since the switching point is fixed in this way, it is possible to set the switching point immediately before the vertical synchronizing signal.

FIG. 2 is a block diagram of the switching signal generating circuit 4a used in the head switching circuit of the first embodiment shown in FIG. The waveform of each part is shown in FIG. In FIG. 2, the reproduction synchronization signal 101 is input to the vertical synchronization signal detection circuit 6 and the vertical synchronization signal 102 is detected. The vertical synchronizing signal 102 is sent to the timer 7 and the timer 8. Timer 7
Responds to the vertical synchronizing signal 102 and its output becomes L for a predetermined time W
After one, that is, at t1, the output signal 103 whose output becomes H is sent to the clock input cp of the D-type flip-flop (FF) 9.
The flip-flop 9 holds the signal level of the magnetic head position signal 105 input to the D input at the output in response to the output signal 103 of the timer 7. As a result, the flip-flop 9 can store the magnetic head position signal 105 at a stable level of the magnetic head position signal 105. This is because the magnetic head position signal 105 is not affected by the change point 108 as shown by the change width 108 because the change point moves due to tape tension or the like. The timer 8 outputs an output signal 104 which becomes L in response to the synchronizing signal 102 and becomes H after a predetermined time W2, that is, at t2, to the clock input cp of the flip-flop 10. The flip-flop 10 sets the signal level of the output of the flip-flop 9 to the output signal 104 of the timer 8.
To Q output in response to. That is, the switching signal generation circuit
4a stores the magnetic head position signal 105 after a predetermined time W1 after receiving the reproduction synchronization signal 101 and outputs the magnetic head position signal 105 as a switching signal 107 after a predetermined time W2, that is, at t2.
This timing t2 is set 3H before the next vertical synchronizing signal, which makes it possible to make the timing later than before.

Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram of a switching signal generating circuit 4b used in the head switching circuit of the second embodiment shown in FIG. Also, FIGS. 5 to 9 show the waveforms of each part in this block diagram. Figure 5 shows the regenerated vertical sync signal.
For 102, a change in the magnetic head position signal 105 occurs within a time width T1 described later. Similarly, FIG. 6 shows that the time period T2, which will be described later, is longer than the time period T1,
Further, FIG. 7 shows a case that does not fall within the time width T2.

In FIG. 4, the reproduction sync signal 101 is input to the vertical sync signal detection circuit 6 and the vertical sync signal 102 is detected.
The vertical synchronizing signal 102 is sent to the timer 7 and the timer 8. The timer 7 outputs an output signal 103 which becomes L in response to the vertical synchronizing signal 102 and becomes H at t1 after a predetermined time W1 to the clock input cp of the D-type flip-flop (FF) 9. The flip-flop 9 holds the signal level of the magnetic head position signal 105 input to the D input at the output in response to the output signal 103 of the timer 7. As a result, the flip-flop 9 can store the magnetic head position signal at a stable level of the magnetic head position signal 105.

The timer 8 ORs the output signal 104 whose output becomes L in response to the synchronization signal 102 and becomes H after a predetermined time W2, that is, at t2.
It is sent to the clock input cp of the flip-flop 10 through the gate 11. The flip-flop 10 holds the signal level of the output of the flip-flop 9 at the Q output in response to the output signal 104 of the timer 8.

On the other hand, the magnetic head position signal 105 is further applied to the edge detection circuit 17 and the switch S2, the edge detection circuit 17 detects the change point of the head position signal 105, and the output of the edge detection circuit 17 shown in FIG. The signal 108 is output to the timer 18 and the AND gate 14. Timer 18 has a predetermined time width T1
And outputs the output signal 109 of the timer 18 to the edge detection circuit 19. The edge detection circuit 19 detects the rising edge of the output signal 109 of the timer 18, and sends the output signal 110 of the edge detection circuit 19 to the OR gate 11. Therefore OR gate 11
The flip-flop 10 which responds to the output signal of the above responds to the output signal 110 of the edge detection circuit 19 or the output signal 104 of the timer 8. Therefore, in the case of the timing shown in FIG. 5, since the output signal 110 of the edge detection circuit 19 shown at H level is within the H level period of the output signal 104 of the timer 8,
It becomes the output signal 111 of the OR gate 11 shown in the figure, and the Q output of the flip-flop 10 becomes the Q output signal 112a of the flip-flop 10 shown in FIG. This Q output signal 112a is sent to the D input of the flip-flop 16. In the flip-flop 16, the reproduction synchronization signal 101 is input to the cp input, and in response to the horizontal synchronization signal in the reproduction synchronization signal 101 immediately after the Q output signal 112a of the flip-flop 10 is input to the D input, the flip-flop 16 outputs the Q output. The output level 113 of the flip-flop 16 is sent to the switch S2 while holding the input level. Therefore, the switching point is performed during the horizontal blanking period to prevent switching noise from appearing on the screen. For example, as shown in FIG. 8, in a certain field, the timing t at which the horizontal synchronizing signal appears immediately after the output timing of the timer 8 which is set to 3.75H of the vertical synchronizing signal.
3, that is, the head switching is performed 3.0H before the vertical synchronizing signal 102. In the next field, as shown in FIG. 9, the head is switched at timing t4, that is, 3.5H before the vertical synchronizing signal 102.

On the other hand, the vertical synchronizing signal 102 is also input to the tire 12, and the timer 12 sends the output signal 114 of the timer 12 which changes after the predetermined time W3 to the timer 13. The timer 13 responds to the timer 12 by changing the output signal 115 of the timer 13 which changes after the time width T2 to A
Send to ND gate 14. Therefore, the output of the AND gate 14 remains L in the case of the timing shown in FIG. That is, the phase difference between the vertical synchronizing signal 101 and the magnetic head position signal is within the time width T2. In this case, the output signal 116a of the AND gate 14 is output, and the timer 15 is sent out, and the timer 15 continues to output the H level. As a result, the switch S2 outputs the output of the flip-flop 16 as the switching signal 107 '. Therefore, the switch S1 switches to the vertical synchronizing signal after a predetermined time has elapsed.

Next, when the magnetic head position signal 105 changes faster than the timing shown in FIG. 6, that is, the output timing of the timer 8, the output signal 111 of the OR gate 11 is the signal of the edge detection circuit 19 and the timer 8 outputs the signal. The flip-flop 10 holds the Q output at L in response to this because it is output slightly earlier than the output signal 104 of the F. The flip-flop 16 holds the Q output at L in response to the horizontal synchronizing signal immediately after this.
On the other hand, since the output signal 108 of the edge detection circuit 17 is generated within the time width T2 indicated by the output signal of the timer 13, A
The timer 15 responsive to these signals through the ND gate 14 does not operate and the switch S2 does not switch. In this case, the switching point is not fixed on the reproduction screen as in the case shown in FIG. 5, but the vertical timing is limited to the time width T1 by the switching timing indicated by the magnetic head position signal 105. Since it comes closer to the ranking period, the switching point is at the bottom of the screen, so it is not noticeable.

Next, there is a timing as shown in FIG. 7, that is, a case where the magnetic head position signal changes earlier than the time width T2. In this case, the magnetic head position signal 105 causes the switch S to be switched because the switching points are considerably included in the reproduction screen and in such a case that the vertical synchronization signal is not reproduced correctly.
I am trying to switch to 1. Therefore, the video signal is not played back, so-called FM dropout does not occur.

Therefore, in the case of the timing state shown in FIG. 7, the output signal 115 of the timer 13 and the output signal 108 of the edge detection circuit 17 cause the AND gate 14 to generate a pulse as shown in the output signal 116 of the AND gate 14 in FIG. Is output to timer 15.
Since the set time of the timer 15 is longer than the vertical synchronization cycle, if this state continues, the timer 15 will be retriggered to L
, The switch S2 turns on the magnetic head position signal.
105 is output to the switch S1 as a switching signal 107 '.

[Effects of the Invention] Since the helical scan type magnetic reproducing apparatus of the present invention is configured as described above, the following effects can be obtained.

In the first embodiment, the position signal from the position detecting means of the magnetic head for switching the video signals reproduced by the plurality of magnetic heads responds to the vertical synchronizing signal of the reproduced video signal, A switching signal generating circuit for storing after a predetermined time and performing the above switching after a second predetermined time is provided. As a result, head switching is performed at a fixed timing with respect to the video signal to be reproduced, so that it is possible to provide a helical scan type magnetic reproducing device capable of fixing the position of the switching point on the screen. It was Therefore, conventionally, there was a switching point at about 6.5H before the vertical synchronizing signal, and noise accompanying it may appear in the screen, but according to this embodiment, for example, at 3H immediately before the vertical synchronizing signal. It is possible to set it, and it has become possible to set the switching point at the timing corresponding to the invisible position at the bottom of the screen. Therefore, switching noise is not noticeable.
Also, when a video tape recorded by a different magnetic recording device is reproduced or tracking adjustment is performed, the switching point does not move on the screen, so that switching noise is not noticeable.

Further, in the helical scan type magnetic reproducing apparatus of the second embodiment, the switching signal is generated by the head position signal so that the switching signal indicating the switching point is performed within a limited range when performing the above switching. Since the switch S2 is provided so as to also generate, it is possible to prevent the switching from being delayed so much that the video signal cannot be reproduced when the video tape recorded by another magnetic recording device is reproduced. Therefore, in the first embodiment, when the head switching is delayed so that the video signal cannot be reproduced, the video signal is reproduced as a white peak level, which causes buzz interference with the audio signal. However, this can be prevented in the second embodiment. Although the video signal cannot be reproduced, the switching noise is not noticeable because the head switching can be delayed by a certain amount when the switching is considerably delayed.

[Brief description of drawings]

FIG. 1 is a block diagram of a head switching circuit of a helical scan type magnetic reproducing apparatus of first and second embodiments of the present invention, FIG. 2 is a block diagram of a switching signal generating circuit of the first embodiment, and FIG. FIG. 4 is a waveform diagram for explaining the first embodiment, FIG. 4 is a block diagram of a switching signal generating circuit according to the second embodiment, and FIGS. 5 to 9 are for explaining the second embodiment. It is a waveform diagram of. 1a, 1b ... Magnetic head, 3 ... Video signal processing circuit, 4 ... Switching signal generation circuit, 6 ... Vertical synchronization signal detection circuit, 7, 8,
12, 13, 15, 18 ... Timer, 9, 10, 16 ... Flip-flop, 11 ... OR gate, 14 ... AND gate, 17, 19 ... Edge detection circuit, 101 ... Reproduction synchronization signal, 102 ... Vertical synchronization signal, 105
... magnetic head position signal, 107, 107 '... switching signal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-269580 (JP, A) Actually opened 53-151418 (JP, U) Actually opened 61-33231 (JP, U)

Claims (1)

[Claims] 1. A plurality of magnetic heads, position signal generating means for generating position signals representing the positions of the plurality of magnetic heads, and video signals reproduced by the plurality of magnetic heads from the position signal generating means. A helical scan type magnetic reproducing device having switching means for switching in response to a position signal, wherein first to third responding to a vertical synchronizing signal of the video signal.
Timer means, first means for responding to the output signal of the first timer means, storing the position signal after a lapse of a first predetermined time after receiving the vertical synchronization signal, and a change point of the position signal First edge detecting means for detecting, fourth timer means for responding to the output signal of the first edge detecting means, and second for detecting a change point of the output signal of the fourth timer means
Edge detecting means, first gate means responsive to the vertical synchronizing signal and the output signal of the second edge detecting means, and after receiving the vertical synchronizing signal in response to the output signal of the first gate means, Second means for reading and outputting the position signal stored in the first means after a second predetermined time longer than the predetermined time of 1, and output of the second means in response to a horizontal synchronizing signal of the video signal. A third means for storing and outputting a signal; a fifth timer means for responding to the output signal of the third timer means; a fifth means for responding to the output signal of the fifth timer means and the output signal of the first edge detecting means; Two gate means, a sixth timer means responsive to the output signal of the second gate means and having a set time longer than a vertical synchronization cycle, and the position signal and the twelfth timer in response to the output signal of the sixth timer means. Three And a switch means for switching the output signal of the means.