JPH0727608B2 - Video tape recorder - Google Patents

Description

The present invention relates to a video tape recorder using a small diameter cylinder and capable of maintaining compatibility with conventional machines.

[Conventional technology]

Conventionally, in a video tape recorder (hereinafter abbreviated as VTR) that uses 1/2 inch tape, one of the methods for realizing the size and weight reduction is to reduce the size of the cylinder while maintaining compatibility with the conventional machine. It is known to do.

As one example thereof, as disclosed in Japanese Patent Laid-Open No. 59-91781, four heads are provided in a cylinder at equal angular intervals,
In addition, the magnetic tape is wound around this cylinder by 270 degrees, and the cylinder is run, and the magnetic tape is sequentially scanned by four heads. In this case, the rotation period of 270 ° in which each head scans the magnetic tape is set to be equal to one field period of the video signal, whereby each head records or reproduces the video signal one field at a time. According to this method, the diameter of the cylinder is 2 heads.
The diameter is about 2/3 of the diameter of the cylinder used for the VTR, and the size of the cylinder can be reduced. Also, by setting the running speed of the magnetic tape so that the relative speed between the head and the magnetic tape is the same as that of the conventional VTR, compatibility with the conventional VTR is maintained.

Further, as another example of reducing the diameter of the cylinder, Japanese Patent Laid-Open No.
As disclosed in Japanese Laid-Open Patent Publication No. 37783, two heads are provided close to a cylinder, and a magnetic tape is wound around the cylinder at an angle θ (however, 270 ° <θ <360 °) to run the video. The video signal from the camera is recorded alternately in two heads, one field at a time. in this case,
The period during which each head rotates by the angle θ is equal to one field period of the video signal from the video camera, and the video camera outputs the video signal only during the period during which the head scans the magnetic tape at the angle θ. . Therefore, when the video camera outputs a 1-field video signal, it stops the output during the period in which the cylinder rotates by (360 ° -θ), and then outputs a 1-field video signal. The video signal is output for each one field. Also in this example, since the video signal of one field is recorded with respect to the winding angle θ of the magnetic tape, the diameter of the cylinder is 180 ° / θ times that of the conventional VTR. When θ = 270 ° as in the previously known example, it becomes 2/3 times. Also in this example, the compatibility with the conventional machine is maintained in the same manner as the above-mentioned known example.

The diameter of the cylinder is about 60 to 70 mm in the conventional two-head type VTR with 180 ° winding, but according to the above-mentioned known example, the former is about 2/3 times 40 to 45 mm.
The diameter is reduced to a certain extent, and if the latter is θ = 300 °, it will be about 3/5 times as large as 36 to 42 mm.

[Problems to be Solved by the Invention] By the way, in recent years, integration of a VTR and a video camera has been promoted, and as one example thereof, what is called an 8 mm video has received much attention. In this 8 mm video, a cylinder having a diameter of 40 mm is used to reduce the size and weight of the VTR portion. However, by applying the above-mentioned known example, this cylinder can be further reduced in diameter.

Therefore, the above-mentioned Japanese Patent Laid-Open No. 59-91781 is used for this 8 mm video.
When the method disclosed in the publication is applied, the diameter of the rotary cylinder can be made extremely small, about 40 × 2/3 = 27 mm. However, it is very difficult to fit four heads in such a small diameter cylinder,
Also, since the diameter of the plane-opposing rotary transformer used must be reduced, it is very difficult to make this rotary transformer into four channels. A coaxial rotary transformer can be made into a four-channel structure, but its thickness is not suitable for miniaturization.

On the other hand, the above-mentioned Japanese Patent Laid-Open No. 59-37783 for 8 mm video.
When the method disclosed in the publication is applied, since recording and reproduction can be performed with two heads, the above-mentioned problems of mounting the head on the cylinder and the rotary transformer do not occur, but each head uses a magnetic tape. Since a non-scanning period occurs and the scanning period of the magnetic tape by each head corresponds to one field period of the video signal, when the reproduction scanning is performed with this 8 mm video, the video signal is intermittently obtained by one field. In the end, there is a problem that it cannot be played back.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video tape recorder that solves the above problems, realizes a smaller cylinder diameter without increasing the number of heads, and enables reproduction.

[Means for solving problems]

To achieve the above object, the present invention provides a cylinder with two heads having different azimuth angles in close proximity to each other so that the cylinder is rotated at a period equal to one field period of a video signal and a magnetic tape is attached to the cylinder. Is rotated by an angle α (where 180 ° <α <360 °), the video signal is time-axis compressed for each field, and the magnetic tape is rotated by the angle α of each head to scan the magnetic tape. Then, the video signal is recorded and reproduced one field at a time.

[Action]

Assuming that the diameter of the cylinder in the present invention is d and the diameter of the cylinder in the conventional 2-head type VTR is D, in order to maintain compatibility between the two, the winding length of the magnetic tape in the cylinder must be equal. Therefore, Since 180 ° <α <360 °, d <D can be achieved and the diameter of the cylinder can be reduced. Since the video signal is time-axis compressed for each field and recorded during the scanning period of the head magnetic tape, it is possible to record the video signal with one head, but alternately record with two heads having different azimuth angles. Therefore, the azimuth recording method is possible as well as the conventional 2-head method VTR, and the compatibility with this can be completely maintained.

In addition, at the time of reproduction, the video signal is reproduced as an intermittent signal for each field, but since each field is compressed in the time axis, by expanding these fields in the time axis, the reproduction signal of the original time axis is reproduced. Is obtained, and reproduction is possible.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First, the cylinder portion will be described.

FIG. 2 is a plan view showing a cylinder portion of a conventional VTR,
FIG. 3 is a plan view showing a cylinder portion in one embodiment of the VTR according to the present invention.

In a conventional VTR, as shown in FIG.
Two heads 51,52 with different azimuths from 0 to 180
The magnetic tape 55 is wound around the cylinder 50 by guide posts 53 and 54 at about 180 ° and runs. In the case of a conventional 8 mm video, the diameter D of the cylinder 50 is 40 mm.

On the other hand, in the embodiment of the present invention, as shown in FIG. 3, two heads 2 and 3 having different azimuth angles are provided close to each other in a cylinder 50, and a guide is provided around the cylinder 50. The magnetic tape 1 is about 270 by the posts 53, 54.
゜ Wrap around and run.

In each of these, one field is recorded and reproduced while each head is rotated by the winding angle of the magnetic tape, and in order to obtain compatibility between the two, a cylinder is used between them. The wrapping length of the magnetic tape must be equal.

Therefore, if the diameter of the cylinder 50 in FIG. 3 is d, So, taking the example of 8mm video, Therefore, the diameter of the cylinder 50 is reduced.

In FIG. 2, the cylinder 50 rotates at a cycle equal to two field periods of the video signal, and each head 51, 52 is divided by 1/2.
Every time the rotating magnetic tape 55 is scanned, a video signal is alternately recorded and reproduced by one field. The heads 51 and 52 start scanning the magnetic tape 55 immediately before one ends the scanning of the magnetic tape 55, so that the video signals are continuously recorded.

On the other hand, in FIG. 3, the cylinder 50 rotates at a cycle equal to one field period of the video signal. Head
2 and 3 alternately record and reproduce the video signal every scanning period of the magnetic tape 1, but the heads 2 and 3 of the 90 ° rotation period are separated from the magnetic tape 1 at the same time, and recording and reproduction cannot be performed during this period. . For this purpose, the video signal is time-axis compressed to 270 ° / 360 ° = 3/4 times for each field, and the time-field-compressed 1-field video signal is scanned by the heads 2 and 3 on the magnetic tape 1. Recording and reproduction shall be performed alternately every 270 ° rotation period. Therefore, two heads 2 and 3 having different azimuths alternately record and reproduce a video signal on the magnetic tape by one field.

From the above, the embodiment of the present invention having the cylinder portion shown in FIG. 3 can maintain compatibility with the conventional VTR shown in FIG. In the case of 8 mm video, the embodiment of the present invention can use a small diameter cylinder of about 26.7 mm as compared with the conventional one, and since only 2 heads are required, it is easy to attach the head to the cylinder. Since the rotary transformer can also be a two-channel type, it is possible to use a thin and small flat type.

Also, at the time of reproduction, the video signal obtained from the heads 2 and 3 is an intermittent signal for each field, but since each field is compressed on the time axis, it is possible to expand the original signal by expanding the time axis on each field. The video signal on the time axis of can be reproduced. Therefore, the embodiments of the present invention are reproducible.

Next, a video signal processing system in one embodiment of the VTR according to the present invention will be described with reference to FIG. In the figure, 1 is a magnetic tape, 2 and 3 are heads, 4 and 5 are rotary transformers, 6 and 7 are switching switches, 8 and 9 are recording amplifiers, and 10 and 1
1 is playback amplifier, 12 and 13 are channel switches, 14 is LPF
(Low-pass filter), 15 frequency converter, 16 chroma processing circuit, 17 ACC (automatic chroma control) circuit, 18 B
PF (Band Pass Filter), 19 for mixed circuit, 20 for HPF
(High-pass filter), 21 FM modulation circuit, 22 emphasis circuit, 23 AGC (automatic gain control) circuit, 24 input terminal, 25 switching switch, 26 output terminal, 27 D / A (analog / digital) ) Converter, 28 is a field memory, 29 is an A / D (analog / digital) converter, 30
Is a switching switch, 31 to 34 are input terminals, 35 is HPF, 36 is FM
A demodulation circuit, 37 is a de-emphasis circuit, 38 is an LPF, 39 is a mixing circuit, 40 is an LPF, 41 is an ACC circuit, 42 is a frequency converter, 43 is a BPF, 44 is a chroma processing circuit, and 45 and 46 are input terminals.

In the figure, during recording, the switching switches 6, 7, 25, 30 are closed to the R side, and a video signal is input from the input terminal 31. This video signal is sent to A / D via switching switch 30.
After being digitized by the converter 29, it is written in the field memory 28. According to the sampling theorem, the sampling frequency in the A / D converter 29 needs to be set to 2f _SC or more when f _SC is the color subcarrier frequency, but here it is selected to be 3f _SC . In the field memory 28, the write clock C _W having a frequency of 3f _SC is supplied from the input terminal 33, whereby the digital video signal output from the A / D converter 29 is written. Further, the field memory 28 is supplied with the frequency 4f _SC read clock C _R from the input terminal 32, whereby the field memory 28 is supplied.
A digital video signal is read from the. This read clock C _R is supplied during the period in which the heads 2 and 3 scan the magnetic tape 1 (that is, in FIG. 3, a 270 ° rotation period during which the heads 2 and 3 scan the magnetic tape 1). During this period, the video signal is time-field compressed 3/4 times by one field and read. The digital video signal read from the field memory 28 is
The D / A converter 27 converts the analog video signal.

The time axis compression operation by the field memory 28 described above is
This will be described with reference to the figure.

FIG. 4 (a) shows 4H (however, H is one horizontal period) within the same field of the video signal before time-axis compression. By writing and reading this in the field memory 28,
As shown in FIG. 4 (b), the time axis is compressed to the length of the 3H period. Further, FIG. 4 (c) shows three fields of the video signal before time base compression, which is the field memory 28.
As shown in FIG. 4 (d), each field is time-compressed to 3/4 times by writing and reading with the length of the 1/4 field period of the original video signal between the fields. Signalless period occurs. Each field period is headed
2 and 3 correspond to the 2/3 rotation period during which the magnetic tape 1 is scanned.

Returning to FIG. 1, the video signal output from the D / A converter 27 (this is referred to as a time-axis compressed video signal because it is time-axis compressed as shown in FIG. 4) is
It is supplied to the BPF 18 and the AGC circuit 23 via the switching switch 25 and separated into a chroma signal and a luminance signal. The chroma signal separated by BPF18 is ACC circuit 17, chroma processing circuit 16,
The chroma signal recording processing system including the frequency converter 15 and the LPF 14 is processed in a well-known manner to obtain a low-frequency converted chroma signal. Also, the luminance signal separated by the LPF included in the AGC circuit 23 is the emphasis circuit 22, the FM modulation circuit.
The luminance signal recording processing system including the 21 and HPF20 is processed in a known manner to obtain an FM-modulated luminance signal.

The video signal output from the D / A converter 27 is
The frequency is 4/3 times higher than that of the original video signal because it is 3/4 times compressed in the time domain. For this reason, the luminance signal and chroma signal separated from this video signal are also 4/3 times the frequency of the original video signal, respectively, and the chroma signal recording processing system and luminance signal processing system for these signals The processing is also performed according to these frequencies. For example, the chrominance subcarrier frequency f _SC ′ of the chroma signal supplied to the frequency converter 15 is 4/3 times the chrominance subcarrier frequency f _SC of the chroma signal in the original video signal. If the color subcarrier frequency of the frequency-converted chrominance signal and f _LSC, the low-frequency converted chroma signal outputted from the frequency converter 15 the color subcarrier frequency f _LSC 'is Therefore, the frequency from the input terminal 24 to the frequency converter 15 must be Carrier wave is supplied. Further, from the same reason, the carrier frequency of the FM-modulated luminance signal output from the FM modulation circuit 21 also needs to be 4/3 times the carrier frequency when the luminance signal of the original video signal is FM-modulated. is there. Although not shown, the low-frequency converted chroma signal and the FM-modulated luminance signal from the LPF14 are mixed in the mixing circuit 19 together with the FM-modulated voice signal and the pilot signal for playback tracking, and the recorded video signal is recorded. Is supplied to the channel switch 12.

Here, the spectrum of the recorded video signal in the conventional 8 mm video is shown in FIG. 5 (a), and the mixing circuit 19
FIG. 5 (b) shows the spectrum of the recording video signal in this embodiment which is output from FIG.
In a conventional 8 mm video shown in FIG. 5 (a), the low-frequency luminance signal and the color subcarrier frequency f _LSC frequency shift f ₁ ~f ₂ is FM modulated 4.2MHz~5.4MHz about 740KHz In addition to the converted chroma signal, a 4-frequency pilot signal having a frequency f _P and an FM-modulated audio signal having a carrier frequency f _A of 1.5 MHz are frequency-multiplexed to form a recorded video signal. The recorded video signal in this embodiment is also as shown in FIG.
Similar signals are frequency-multiplexed, but these frequencies f ₁ ′, f ₂ ′, f _LSC ′, f _P ′, f _A ′ are 4/3 of the corresponding frequencies in FIG. 5 (a). It is doubled.

Returning to FIG. 1, the channel switch 12 has an input terminal 46.
With a switching signal of 30 Hz from, for example, the heads 2 and 3 are switched immediately before contact with the magnetic tape 1. When the channel switch 12 is closed to the A side, the recording video signal output from the mixing circuit 19 is the channel switch 12, recording amplifier 8,
The recording video signal, which is supplied to the head 2 via the switching switch 6 and the rotary transformer 4 and the head 2 rotates 270 °, is recorded during the scanning period of the magnetic tape 1 and the time axis compression of which is 1 field is recorded on the magnetic tape 1. . When this recording is completed, the heads 2 and 3 are separated from the magnetic tape 1, and the channel head 12 is switched to the B side immediately before contacting the magnetic tape 1. Then, the next 1-field time-axis-compressed recording video signal is supplied to the head 3 via the channel switch 12, the recording amplifier 9, the switching switch 7 and the rotary transformer 5, and the magnetic tape 1 is rotated during the 270 ° rotation period. Recorded in.

At the time of reproduction, the switching switches 6, 7, 25, 30 are switched to the P side. The heads 2 and 3 are tracking-controlled by a control system (not shown) based on the pilot signal so that the heads 2 and 3 reproduce and scan the tracks in the magnetization direction corresponding to the azimuth angles on the magnetic tape 1. Further, the channel switch 13 receives the switching signal from the input terminal 46, and the head 2
Is closed to the A side when reproducing and scanning the track in the magnetization direction that matches the azimuth angle, and B when the head 3 reproduces and scans the track in the magnetization direction that matches the azimuth angle.
Controlled to close to the side.

The reproduced video signal, which is reproduced in the head 2 and is compressed on the time axis every other field, is transmitted through the rotary transformer 4, the switching switch 6 and the reproducing amplifier 10 to the channel switch.
The other time-compressed reproduction video signal supplied to the head 13 and reproduced in the head 3 is supplied to the channel switch 13 via the rotary transformer 5, the switching switch 7 and the reproduction amplifier 11. Channel Switch 13
Then, these reproduced video signals are mixed so as to interpose each other.

The mixed video signal is supplied to the HPF 35 and the LPF 40, and is separated into the FM-modulated luminance signal and the low-pass converted chroma signal having the color subcarrier frequency f _LSC ′. The FM-modulated luminance signal is subjected to a well-known process in a luminance signal reproduction processing system including an FM demodulation circuit 36, a de-emphasis circuit 37, and an LPF 38 to obtain a luminance signal that is time-axis compressed. Also, LP
The chroma signal separated by F40 is subjected to a well-known process in the chroma signal reproduction processing system including the ACC circuit 41, the frequency converter 42, the BPF 43 and the chroma processing circuit 44, and the color subcarrier frequency is time-axis compressed to f _SC ′. A chroma signal is obtained. To this end, the frequency converter 42 has an input terminal 45
From a carrier of frequency | f _SC ′ −f _LSC ′ |.

The time-axis-compressed luminance signal and chroma signal are mixed by the mixing circuit 39, and are supplied to the A / D converter 29 as a time-axis-compressed video signal through the switching switch 30 to be digitalized and the field memory 28. Written in. At this time, the write clock C _W having a frequency of 4f _SC is supplied from the input terminal 33 to the field memory 28. In addition, the frequency is input from the input terminal 32 to the field memory 28.
Read clock C _R of the 3f _SC is supplied, thereby, digitized video signals are read out is extended shaft 4/3 times time. Therefore, this video signal becomes a signal on the same time axis as the video signal supplied from the input terminal 31 during recording.

The video signal read from the field memory 28 is D / A
Converted to an analog signal by the converter 27 and switched
It is supplied to the output terminal 26 via 25.

As described above, in this embodiment, reproduction is also possible.

FIG. 6 is a block diagram showing the time axis compression / expansion circuit in FIG. 1, in which 60 and 61 are input terminals, 62 is an output terminal, and 6
Reference numeral 3 is a sync signal separation circuit, 64 is a write control circuit, 65 is a read control circuit, 66 and 67 are oscillators, and 68 and 69 are switching switches. The same reference numerals are given to the portions corresponding to FIG.

In FIG. 6, at the time of recording, the switching switches 68 and 69 are closed to the R side by the control signal from the input terminal 61, and the oscillator 6
A signal having a frequency of 3f _SC is supplied from 6 to the A / D converter 29 and the write control circuit 64 via the switching switch 68, and the oscillator
A signal having a frequency of 4f _SC is supplied from 67 to the read control circuit 65 via the switching switch 69. The video signal to be recorded is supplied from the input terminal 60 to the A / D converter 29 and the sync signal separation circuit 63.

In the A / D converter 29, this video signal is digitized into 3f _SC sample and held, and the field memory 28
Is supplied to. The sync signal separation circuit 63 separates the sync signal from the video signal and supplies the sync signal to the write control circuit 64.

Therefore, in the field memory 28, the frequency from the write control circuit 64 whose timing is controlled by this synchronization signal is 3f.
The write clock C _W of _SC writes the digitized video signal supplied from the A / D converter 29, and at the same time, the frequency from the read control circuit 65 is changed.
The read clock C _R of 4f _SC, reading of the video signal. The read video signal is converted into an analog signal by the D / A converter 27. This video signal is the video signal input from the input terminal 60 compressed in time by 3/4, and supplied from the output terminal 62 to the slicing switch 25 (FIG. 1).

During reproduction, the switching switches 68 and 69 are switched to the P side. The operation at this time is that the reproduction video signal input from the input terminal 60 is time-axis compressed to 3/4 times the original video signal, and the frequency 3f _SC signal output from the oscillator 66 is input to the read control circuit 65. The same as during recording except that the signal of the frequency 4f _SC supplied and output from the oscillator 67 is supplied to the A / D converter 29 and the write control circuit 56. Therefore, the output terminal 52 is connected to the input terminal 60. The video signal of the original time axis, which is 3/4 times the time axis extension of the video signal supplied to, is obtained.

Table 1 below shows the comparison between the specifications of the current standard 8 mm video and the small diameter 8 mm video in which the cylinder diameter is ⅔ times by applying the above embodiment.

Table 1 is for NTSC video signals,
The same relationship applies to CCIR video signals.

FIG. 7 is a block diagram showing a video signal processing system in another embodiment of the VTR according to the present invention. 70 and 71 are detection circuits, 72 is a comparator, 73 is a switching switch, and 74 is an input terminal. The parts corresponding to those in FIG.

This embodiment also enables search reproduction without a noise bar, and the operations for recording and normal reproduction are exactly the same as those of the embodiment shown in FIG. For this reason, the channel switch 12 is effective at the time of recording, and is switched alternately by the switching signal A of 30 Hz from the input terminal 46 on the A side and the B side. However, the channel switch 13 is used during normal reproduction and search reproduction. During normal reproduction, the control signal S from the input terminal 74 causes the switching switch 73 closed to the b side to switch the switching switch 73. The 30 Hz switching signal A supplied from the input terminal 46 causes the A and B sides to alternate. , And during search playback, a
A side A and B side are alternately switched by a switching signal C supplied from a comparator 72 via a switching switch 73 closed to the side.

Next, the operation during search reproduction of this embodiment will be described with reference to FIGS. 8 and 9.

Assuming that a track pattern is formed on the magnetic tape 1 by the azimuth recording method as shown in FIG. 8 (here, indicates a track having a different magnetization direction), each head 2, 3 is a track. In the normal reproduction in which the reproduction scanning is performed in the direction indicated by the arrow 104 parallel to, the heads 2 and 3 reproduce and scan the tracks corresponding to these azimuth angles. Therefore, as in the embodiment shown in FIG. Switch 73
To the b side and connect the channel switch 13 from the input terminal 46.
By switching to the A side and the B side by the switching signal A of 30 Hz (Fig. 9 (A)), the channel switch 13 compresses the time axis with a constant amplitude as shown in Fig. 9 (E). A good video signal is obtained.

By the way, during search playback, changeover switch 6,7,
25 and 30 are closed to the P side, and the switching switch 73 is closed to the a side.
At this time, in FIG. 8, the reproduction scanning direction of each of the heads 2 and 3 becomes an oblique direction with respect to the track, as shown by an arrow 105, and one reproduction scanning crosses a plurality of tracks. For this reason, the video signal F reproduced at the head 2 and supplied to the A side of the channel switch 13 does not have a constant amplitude, but as shown in FIG.
The amplitude becomes large when the track corresponding to the azimuth angle of 1 is being reproduced and scanned, and the amplitude decreases as it deviates from this, and the video signal G reproduced at the head 3 and supplied to the B side of the channel switch 13 is also the same. However, as shown in FIG. 9 (G), the amplitude becomes large when the track corresponding to the azimuth angle of the head 3 is being reproduced and scanned, and the amplitude decreases as it deviates from these. Therefore, the video signals F and G are supplied to the channel switch 13 at the switching signal A of 30 Hz from the input terminal 46.
When switched with, a noise bar appears on the reproduction screen in a portion where the amplitude of these video signals F and G is small.

By the way, when one of the video signals F and G has a large amplitude, the other has a small amplitude. Moreover, heads 2, 3
Are very close to each other, the information contents of the video signals F and G at the same time are almost the same.

Therefore, the video signals F and G are also supplied to the detection circuits 70 and 71, respectively, and their envelopes are detected. By comparing these envelopes by the comparator 72, the switching signal C is detected.
(FIG. 9 (C)) is formed. This switching signal C is supplied to the channel switch 13 via the switching switch 73. As a result, the channel switch 13 closes to the A side when the amplitude of the video signal F is larger than the amplitude of the video signal G, and closes to the B side when the amplitude of the video signal F is smaller than the amplitude of the video signal G. Therefore, the channel switch
From 13, as shown in FIG. 9 (E '), a video signal with greatly reduced amplitude fluctuation is obtained. according to this,
Noise bars on the playback screen are significantly reduced.

In the above embodiments, the winding angle of the magnetic tape around the cylinder is 270 °, and the cylinder diameter is 2/3 times the conventional diameter. However, this winding angle α is larger than 180 °. For example, the diameter of the cylinder can be reduced while maintaining compatibility with conventional VTRs. Below is a description of this in Fig. 10 ~
This will be described with reference to FIG.

Now, in FIG. 10, assuming that the winding angle of the magnetic tape 1 with respect to the cylinder 50 is α and the diameter of the cylinder 50 is d _1, and the conventional VTR shown in FIG. 2 is kept compatible, Has to have the same amount of winding around both cylinders, Was established, and from now on, Becomes Here, if 180 ° <α <360 °, d ₁ <D, and the diameter of the cylinder 50 can be reduced. In this case, the cylinder 50 makes one rotation at one field of the video signal, and one field of the video signal compressed on the time axis during the rotation period of α degrees is recorded. Therefore, the time base compression of the video signal to be recorded is Becomes Therefore, when the frequency of the write clock of the field memory is f (however, f> 2f _SC ) during recording,
The frequency of the read clock Thus, the time axis compression of D / 2d ₁ times can be performed. Also,
During playback, set the frequency of the write clock in the field memory. Then, by setting the frequency of the read clock to f, the original signal with a compression ratio of 1 can be restored.

FIG. 12 shows the frequency spectrum of the recording signal. As explained in FIG. 5, in the case of a small diameter cylinder with a diameter of d ₁ , the color sub-channel of the chroma signal before conversion to the reduction has the carrier frequency And the frequency deviation of the FM luminance signal Reduces the color subcarrier frequency of the converted chroma signal The carrier frequency of the FM modulated audio signal The frequency of the pilot signal Need to

2 and 3 in which the azimuth angles are different from each other in FIGS.
The two heads make up a double azimuth head. FIG. 11 shows the sliding surface of the double azimuth head, and the gap between the gears will be described with this.

In the figure, head 3 is an azimuth head and head 2 is an azimuth head. This double azimuth head is formed on the magnetic tape 1. The track pattern is shown in FIG. The track 102 is a track formed by the azimuth head 2, and the track 10
Reference numeral 3 is a track formed by the azimuth head 3, and is marked with + and-symbols, respectively.

When signals are continuously recorded with such a double azimuth head, in order to maintain compatibility with the conventional two-head VTR, the H line between adjacent tracks on the magnetic tape must be the same as the above conventional VTR. is necessary. Therefore, 1H of the video signal before time axis compression is However, if this is set to 1T, the head 2 in Fig. 11,
The gear gap distance g of 3 may be set by the following equation.

g = nT (however, n = 1,2,3 .........) Although the embodiment of the present invention has been described by taking the 8 mm video standard as an example, the present invention can be applied to other household VTRs. There is no end.

〔The invention's effect〕

As described above, according to the present invention, the diameter of the cylinder can be made smaller than that of the conventional two-head type VTR, and recording / reproduction by the two-head type VTR can be performed.
It is possible to maintain compatibility with the above, and the two-head configuration enables specification of a rotary transformer of a plane opposing type, and it is possible to obtain an excellent effect that the overall size and weight of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a video signal processing system in an embodiment of a video tape recorder according to the present invention, FIG. 2 is a plan view showing a cylinder portion of a conventional 2-head system video tape recorder, and FIG. FIG. 4 is a plan view showing a cylinder portion in an embodiment of a video tape recorder according to FIG.
FIG. 5 is a diagram for explaining the operation of the time axis compression / expansion circuit in FIG. 1, FIG. 5 (a) is a frequency spectrum diagram of a recording signal in a conventional 2-head video tape recorder, and FIG. 5 (b) is in FIG. FIG. 6 is a block diagram showing a frequency spectrum of a recording signal, FIG. 6 is a block diagram showing a time axis compression / expansion circuit in FIG. 1, and FIG. 7 is a block diagram showing a video signal processing section in another embodiment of the video tape recorder according to the present invention. FIG. 8 is a schematic diagram showing the scanning direction of the head on the magnetic tape during normal reproduction and search reproduction, and FIG. 9 is a waveform diagram showing signals at various parts during normal reproduction and search reproduction in FIG. FIGS. 10 to 13 are for explaining the video tape recorder of the present invention in a general manner.
Figure is a plan view showing the cylinder section. Figure 11 is a plan view of the double azimuth head used in the cylinder section shown in Figure 10 as seen from the sliding surface side. Figure 12 is a frequency spectrum diagram of the recording signal. Figure 13 FIG. 4 is a track pattern diagram on the magnetic tape. 1 …… Magnetic tape, 2,3 …… Head, 26 …… Video signal output terminal, 27 …… D / A converter, 28 …… Field memory, 29 …… A / D converter, 31 …… Video signal input terminal , 50 …… Cylinder.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 5/92 9/83 Z

Claims (4)

[Claims] 1. Two heads having different azimuth angles are attached to a cylinder in close proximity to each other, and the head is rotated at a rate of one revolution during one field period of the video signal input to the cylinder, and a magnetic tape is provided around the cylinder. ∘ (however, 180 ° <α ° <360 °) wrapped around the cylinder and run, (However, D is a video tape in which two heads are wound about 180 ° around a cylinder attached at an angular interval of 180 °, a magnetic tape is run, and a video signal is recorded / reproduced by one field each at the head. The diameter of the cylinder in the recorder), and the time axis compression means time axis compresses the input video signal by D / 2d times for each field, and rotates the magnetic tape while the head is making one rotation. The time-axis-compressed video signal is alternately recorded by the head for each period, and the time-axis-compressed video signal reproduced by the head is recorded by the time-axis decompressing unit for each field. In the video tape recorder configured to be expanded by 2d / D times in the time axis so that the original time axis video signal can be restored, the input video signal is a color video signal, and Frequency shift the luminance signal between base-compressed video signal (Where f _{1 to} f ₂ are the frequency deviations of the frequency-modulated luminance signal in the video tape recorder using a cylinder of diameter D), and the chroma signal of the time-axis-compressed video signal. The color sub-carrier frequency is (Provided that f _LSC is the color sub-carrier frequency of the chroma signal converted to the low frequency in the above-mentioned video tape recorder using the diameter D cylinder), and recorded and reproduced at the time of reproduction. The luminance signal thus reproduced is frequency-demodulated, and the reproduced low-frequency conversion chroma signal is frequency-converted into a chroma signal having the same color subcarrier frequency as the chroma signal at the time-axis compression. A video tape recorder characterized in that the signal and the time axis are expanded by the time axis expanding means. 2. The video tape recorder according to claim 1, wherein the rotary transformer connecting the head and the signal processing system is of a plane facing type. 3. The time axis compression means and the time axis expansion means according to claim 1 or 2, wherein the time axis compression means and the time axis expansion means also serve as an A / D converter, a field memory and a D / A converter. , The sampling clock frequency of the A / D converter and the write clock frequency of the field memory are f, and the read clock frequency of the field memory is During playback, set the sampling frequency of the A / D converter and the write clock frequency of the field memory. And a read frequency of the field memory is set as f. 4. Claims 1, 2 or 3
In the paragraph 1, there are provided first and second detection circuits that detect the head reproduction signal, and a comparison circuit that compares the detection outputs of the first and second detection circuits in amplitude. The video tape recorder is characterized in that the channel switch is switched and controlled by the output signal of (1) to select a reproduction signal having a larger amplitude among the reproduction signals of the head.