JPH07121842A - Video tape recorder - Google Patents

Abstract

PURPOSE:To enable continuing a normal recording even when the clogging of a head is generated by detecting the clogging with a simple constitution. CONSTITUTION:A clogging detecting signal (d) is written in a certain track by a recording and reproducing head 14. The recording and reproducing head 14 reads out a detection pulse (d') including the clogging detecting pulse (d) during scanning adjacent tracks. The detection pulse is compared with a threshold value by a comparator 58 included in a clogging detecting circuit 30 and it is judged that the clogging is not generated in the head 14 when the detection value is larger than the threshold value and it is judged that the clogging is generated in the head when the detection value is smaller than the threshold value. A detection pulse (h) of a high level is supplied to a counter 62 and then a head changing over switch 46 selects a replacement head 16 by the control of a channel selector 66. That is, the recording and reproducing head 14 is changed over to the replacing head 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape recorder, and more particularly to a helical scan type video tape recorder (VTR) such as 8 mm or VHS.

[0002]

2. Description of the Related Art Conventionally, in a helical scan VTR, head clogging has been an unavoidable problem. Since recording cannot be performed normally when clogging occurs, there is a particular problem when recording a subject that cannot be retaken, such as recording with a camera-integrated VTR. As a solution to this problem, for example, Japanese Patent Laid-Open No. 1-30410 (G1)
1B 5/09), a system has been proposed in which a monitor head is provided separately from the recording / reproducing head and recording is performed while detecting clogging by the monitor head during recording. ing.

[0003]

However, in this prior art, when the clogging is detected by the output of the monitor head, the means for discriminating whether the clogging is caused by the recording / reproducing head or the monitor head is provided. You will need it. In addition, a monitor head for determining a clogging and a video memory for recording a video on a tape when the clogging is required require a complicated structure.

Therefore, a main object of the present invention is to provide a video tape recorder which can detect clogging with a simple structure.

[0005]

According to the present invention, when a signal is written in a first track, a clogging detection signal is written in a predetermined area of the first track, and a signal is written in a second track adjacent to the first track. A video tape recorder is provided with a first head that occasionally reads a clogging detection signal of a first track, and a clogging detection means that detects clogging of the first head according to the read state of the clogging detection signal.

[0006]

The clogging detection signal written on the first track by the first head is read by the first head while the first head is scanning the second track. When the level of the read clogging detection signal is higher than the threshold value, it is determined that the first head is not clogged, and when it is equal to or lower than the threshold value, it is determined that the first head is clogged. When the second head and the head switching means are further included, the head switching means outputs the second head to the second head in response to the signal indicating that the clogging of the first head is detected, which is output from the clogging determining means. Switch to head.

[0007]

According to the present invention, the clogging of the head can be detected with a simple structure without using a monitor head or a memory unlike the conventional case. Further, if the head being used is clogged, the head is switched to the spare head, so that normal recording can be continued even if the head is clogged.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, in a helical scan VTR, azimuth recording is usually performed to increase the recording density. This utilizes a characteristic that a high-frequency signal of 1 MHz or more cannot obtain a sufficient output unless the head has the same azimuth as that at the time of recording. That is, by changing the azimuths of the heads of the odd-numbered track and the even-numbered track, data can be recorded without providing a gap between the tracks. However, for example, 10
Azimuth does not have much influence on a signal having a frequency of about 0 kHz, and a signal on an adjacent track is detected as crosstalk. The azimuth loss L is expressed by Equation 1.

[0010]

[Equation 1]

A device utilizing this is, for example, 8 mmV
There is a TR tracking method. In this tracking method, head tracking can be performed by comparing the levels of signals (pilot signals) of about 100 kHz recorded on both tracks adjacent to the track being scanned by the head. This example
100 kHz to 500 kHz for detecting clogging of the head
A signal for a certain amount of time, and apart from an area for writing original information such as a video signal, a certain short period (1H
(About ~ 2H), the clogging detection signal is written to the next track at the same timing, and the clogging detection signal recorded on the previous track is read out. is there.

The VTR 10 of this embodiment shown in FIG. 1 is applied to, for example, an 8 mm VTR, and as shown in FIG. 2, it is a regular recording / reproducing device including heads 14a and 14b mounted on the rotary drum 12 so as to face each other by 180 °. Head 14
including. Similarly, the replacement head 16 for clogging including the heads 16a and 16b and the replacement head 18 for clogging including the heads 18a and 18b are mounted on the rotary drum 12, respectively.

Returning to FIG. 1, the recording / reproducing head 14 and the alternative heads 16 and 18 are respectively provided with a switch 20 and a switch 20.
22 and 24. Further, on the rotary drum 12, magnets 26a and 26b for detecting the rotational phase are provided.
Is attached. The magnets 26a and 26b are N
It is attached so that the polarity of / S is reversed. And
By detecting a magnetic change caused by the magnets 26a and 26b by the rotary phase detector 28, the rotary drum 12
To detect the rotation phase of. As the rotation phase detector 28,
For example, a coil, an MR element, a Hall sensor, etc. are used to convert a magnetic change into a voltage. The voltage is amplified by the amplifier 32 included in the clogging detection circuit 30, and the amplifier output a as shown in FIG. The pulses α and α'of the amplifier output a are signals by the magnet 26a,
The pulses β and β'are signals generated by the magnet 26b. Then, in the window comparator 34, the amplifier output a is set by appropriately setting the window width.
From this, a binary pulse b as shown in FIG. 3B can be obtained, and the pulse is given to the switches 20, 22 and 24 as an RFSW pulse via the delay circuit 36. This RFSW pulse causes the heads 14a and 14
b, 16a and 16b, and 18a and 18b, respectively.

Further, the pulse b is given to the timing generation circuit 40 via the delay circuit 38, and the timing generation circuit 40 applies the gate pulse c as shown in FIGS. 3 (C) and 3 (H) to the switch 42. Output. When the gate pulse c is low level (normal), the switch 42 is connected to the terminal 42a side. At this time, the recording signal r from the terminal 44 is input, and one of the heads selected by the head changeover switch 46 causes the tape 47 (see FIG.
(A)). Hereinafter, the head changeover switch 4
6 is connected to the switch 20 and the recording / reproducing head 14 is selected. At this time, the recording signal r
Is written on the tape 47 by the recording / reproducing head 14. The switching operation of the head changeover switch 46 is
It is controlled by a channel selector 66 (described later). The recording signal r is, for example, a video signal or a digital signal.

On the other hand, the switch 42 is connected to the terminal 42b side while the gate pulse c is at the high level. Depending on the high level period of the gate pulse c,
The clogging detection signal area X (FIGS. 5A and 5B) of the track formed on the tape 47 is determined. The clogging detection signal area X is, for example, a PC on a truck.
It is provided between the M area 49a and the video area 49b.
The clogging detection signal area X is divided into an area W for recording the clogging detection signal d from the oscillator 50 and an area R for reproducing the clogging detection signal d. Then, as can be seen by comparing the tracks 56a and 56b, for example,
The area W of the track scanned first in time series and the area R of the track scanned later are adjacent to each other.

That is, when the gate pulse e (FIGS. 3D and 3I) output from the timing generation circuit 40 is at the high level, the switch 48 is connected to the terminal 48a side, and the clogging detection signal d is supplied to the area. W is written. Switch 4 when gate pulse e is low level
8 is connected to the terminal 48b side, and the clogging detection signal d written in the adjacent track is read in the area R. Here, the oscillation frequency and the signal strength of the clogging detection signal d are set in consideration of the azimuth loss so that the signals of the adjacent tracks can be sufficiently picked up. And
When the clogging detection signal d is written, the clogging detection signal d is written in the area W as it is. On the other hand, when the clogging detection signal d is read, the signal reproduced by the recording / reproducing head 14 is amplified by the amplifier 52,
The bandpass filter 54 extracts a detection pulse d ′ including the clogging detection signal d as shown in FIG.

Track 5 shown in FIGS. 5A and 5B.
6A, 56b and 56c, when the recording / reproducing head 14 is not clogged, the clogging detection signal d written in the previous track can be continuously read in the next track. . That is, when the recording / reproducing head 14 is switched to the reproduction state when the area (area R) adjacent to the area W in which the clogging detection signal d is written is crossed, the clogging detection signal written in the previous track. Read d. Therefore, the level of the detection pulse d ′ shown in FIG. 3 (E) does not decrease, and therefore the level of the detection pulse f (FIG. 3 (F)) obtained by sample-holding by the sample-hold circuit 56 also does not decrease. Therefore, when the comparator 58 compares the detection pulse f with a predetermined threshold value and detects the level of the detection pulse f,
As shown in (G), the high-level detection pulse g is obtained, and it can be seen that the recording / reproducing head 14 is not clogged.

On the other hand, when the recording / reproducing head 14 is clogged and the recording pattern is lost like the track 56d shown in FIG. 5A, the clogging detection signal is output as shown in FIG. 5B. It becomes impossible to write and read d. Therefore, since the level of the detection pulse d'shown in FIG. 3 (E) is lowered, the level of the detection pulse f from the sample hold circuit 56 is also lowered. Therefore, when the level of the detection pulse f is detected by the comparator 58, a low-level detection pulse g is obtained, and it is understood that the recording / reproducing head 14 is clogged. That is, when clogging is detected in a certain track, it can be determined that the head 14a (or 14b) recording the previous track or the head 14b (or 14a) currently recording is clogged.

When clogging occurs in this way, the heads are switched as follows. This will be described with reference to FIG. In the initial state, the counter 62 is cleared by the stop signal given from the system controller (not shown) through the terminal 64. Therefore, in the initial state, the channel selector 66 and the head changeover switch 4 are
6, the recording / reproducing head 14 is selected.

When the clogging detection circuit 30 detects clogging of the recording / reproducing head 14, FIG.
A low-level detection pulse g as shown in FIG. 4A is applied to the inverter 60, and the inverter 60 outputs a high-level detection pulse h shown in FIG. 4B as an inverted output. The detection pulse h triggers the counter 62 to operate, and the counter 62 counts the number of clogging.

That is, when the clogging detection circuit 30 detects clogging of the recording / reproducing head 14, the high-level detection pulse h causes the counter 62 to operate and count up. Then, under the control of the channel selector 66, the head changeover switch 46 is replaced with the alternative head 1
Select 6. That is, the head is the recording / reproducing head 1.
4 to the alternative head 16. If the alternative head 16 is normal, the clogging state is resolved, the detection pulse g is at a high level, the detection pulse h is at a low level, and the detection pulse h is thereafter at a low level until the alternative head 16 is clogged. Keep keeping. After that, when the substitute head 16 is clogged, the detection pulse h
Changes from low level to high level, the counter 62 counts up again. Then, the head changeover switch 46 selects the alternative head 18 under the control of the channel counter 66. That is, the head is switched from the alternative head 16 to the alternative head 18. In this way, when the clogging occurs again, the same operation as described above is performed, but when the alternative head for clogging is used up, the detection pulse h remains at the high level. At this time, as shown in FIG. 4C, the over signal i output from the AND gate 68 becomes high level. When the alternative heads 16 and 18 are clogged from the beginning, the detection pulse g as shown in FIG.
Remains at the low level, and the detection pulse h remains at the high level as shown in FIG. 4 (E), which indicates that the clogging state could not be eliminated. That is, terminal 7
By observing the detection pulse h from 0, it is possible to know whether or not the head is in the clogging state.

The channel selector 66 will be described here. The channel selector 66 includes a counter 62
For example, a 2-bit signal is supplied to the head changeover switch 46 after being converted into a 3-bit signal.
For example, when the counter 62 supplies a signal “00” to the channel selector 66, the channel selector 66
Outputs a signal "110" to the head changeover switch 46, and the head changeover switch 46 selects the recording / reproducing head 14. Further, when the signal “01” is given to the channel selector 66, the signal “101” is output, the head changeover switch 46 selects the alternative head 16, and the channel selector 66 is turned to “10”. When a signal is given, a signal of "011" is output and the head changeover switch 46 selects the alternative head 18. Incidentally, when the counter 62 outputs the signal "11", the AND gate 68 outputs the high-level over signal i to notify that the head clogging cannot be eliminated. If the head changeover switch 46 is directly controlled by the signal from the counter 62, the channel selector 66 can be omitted.

As described above, according to the VTR 10 of this embodiment, the clogging state of the head can be detected at the time of recording by the detection pulse h, and the head is switched one after another whenever clogging occurs, and clogging occurs. No head can be used sequentially. Therefore, by attaching a plurality of spare heads, it is possible to perform normal recording even when the head is clogged, and the clogging recording hardly occurs.

In the above embodiment, the VTR 10 is 8
Although the case where the present invention is applied to the mmVTR has been described, the present invention is not limited to this and can also be applied to a VHS type VTR. As shown in FIG. 6, there is a margin 74 defined by the standard between the video track 70 and the control track 72, which is approximately 0.3 mm. By providing a clogging detection signal area X ′ similar to the clogging detection signal area X shown in FIG. 5B in this margin 74, the present invention can be applied to a VHS type VTR. As described above, by providing the clogging detection signal area X'on the track, even when the present invention is applied to the VHS type VTR, the same effect as that of the above-described embodiment can be obtained.

In the above-mentioned embodiment, two sets of replacement heads for clogging are prepared, but the number of replacement heads for clogging is not limited to this and any number may be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an illustrative view showing each head attached to a rotary drum.

FIG. 3 is a timing chart showing main signals for explaining the clogging detection processing of this embodiment.

FIG. 4 is a timing chart showing main signals for explaining the head switching processing of this embodiment.

5A is a schematic diagram showing a recording pattern when a clogging occurs, and FIG. 5B is an illustrative view showing a recording / reproducing pattern of a clogging detection signal.

FIG. 6 is an illustrative view showing a tape format when the present invention is applied to a VHS type VTR.

[Explanation of symbols]

 10 ... VTR 12 ... Rotating drum 14 ... Recording / reproducing head 16, 18 ... Alternative head for clogging 30 ... Clogging detection circuit 46 ... Head changeover switch 62 ... Counter 66 ... Channel selector X, X '... Clogging detection signal Area W: Area for recording the clogging detection signal R: Area for reproducing the clogging detection signal

Claims (2)

[Claims] 1. When writing a signal to a first track, a clogging detection signal is written to a predetermined area of the first track, and when writing a signal to a second track adjacent to the first track, the first track is written. A video tape recorder, comprising: a first head for reading the clogging detection signal, and clogging detection means for detecting clogging of the first head according to the read state of the clogging detection signal. 2. A spare second head, and head switching means for switching between the first head and the second head, wherein the head is detected when clogging of the first head is detected by the clogging determination means. The video tape recorder according to claim 1, wherein the first head is switched to the second head by switching means.