JPH04156093A - Magnetic picture recording device - Google Patents

Abstract

PURPOSE:To prevent the automatic phase control(APC) of a chromaticity signal circuit at the time of reproducing an image by aligning the phase shifting direction (or existence) of a low frequency conversion chromaticity signal. CONSTITUTION:A magnetic tape 4 positioned by inclination pins 7A, 7B is wound around almost the whole periphery of a rotary head drum 6 and video heads 8A, 8B having mutually different azimuth values are adjacently fixed on the same height. Since it is impossible to simultaneously position the heads 8A, 8B on the upper and lower ends of the tape 4, a signal is added for a slight time interval before and after time kV at the time of executing time base compressing operation to form recording tracks 10A, 10B having an overlap period shown by net line parts. Consequently, the phase shifting direction (or existence) of low frequency conversion chromaticity signals is aligned in one recording track including the overlap recording period, so that the APC of the chromaticity signal circuit can be prevented from being disturbed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording device that is required to be small and lightweight, such as a camera-integrated VTR.

[Conventional technology]

Generally, in a VTR, recording and playback is performed by winding a magnetic tape around a rotating head drum that has two video heads mounted 180 degrees opposite each other (in opposite azimuths to each other).
Many of them are commonly known as 2-head helical scan type.

On the other hand, in VTRs using the chromaticity signal low-pass conversion recording method such as 8mm video, VH8, and β, for example, ``Image Recording and Playback'' (Corona Publishing, May 1978).

As described in PP408-411), the phase shift of the chromaticity signal subcarrier is performed for each horizontal period.

This is to remove interference from adjacent tracks during playback.

According to VTR standards, when recording with the +azimuth head, there is no phase shift, and when recording with the -azimuth head, there is a phase shift of 180 degrees per horizontal period, and both heads are in opposite directions to each other, 90 degrees per horizontal period. There are things that record while shifting.

[Problem to be solved by the invention]

The above-mentioned chromaticity signal processing method during recording includes A P C (Automatic Phase
There are factors that cause disturbances to the control and cause flickering and the like.

In other words, as shown in the plan view of the area around the rotary head drum in Figure 2, the above-mentioned 180 degree winding of the two heads is similar to that of a VTR.
Now, two video heads LA.

A magnetic tape 4 is wound over 180 degrees around the rotary head drum 2 on which the IB is mounted using inclined pins 3A and 3B for recording and reproduction. The arrows in the figure indicate the running direction of the magnetic tape 4 and the rotation direction of the rotary head drum 2.

The rotary head drum 2 rotates once every two fields, and the video heads LA and IB alternately record and reproduce signals one field at a time; (a=approximately 10 degrees), an overlapping period of recording occurs.

The recording pattern on the magnetic tape 4 at this time is shown in the explanatory diagram of FIG.

Recording tracks 5A and 5B are video heads IA and IB, respectively.
is formed. The white part in Figure 2 shows that only one of the heads is in contact with the magnetic tape (18o-a).
The shaded area is the overlap winding period a in Figure 2.
formed between.

Therefore, the hatched part on the exit side (upper side in the figure) of 5B and the
The same signal is recorded in the shaded area on the input side (lower side in the figure).

On the other hand, although not shown, the rotary head drum 2 in FIG. 2 is equipped with a tack pulse generator that indicates the rotational phase.
For example, when there is, it is Low.

- Generates a logic signal that goes High when the azimuth head IB is present. The switching point of this logic signal is the third
As indicated by M and N in the figure, this is the central part of the overlap period. The phase shift direction (or presence or absence) of the chromaticity signal subcarrier to be recorded is also determined by this logic signal. Therefore, in the overlap period indicated by diagonal lines in FIG. 3, M.

Outside the position indicated by N (on the edge side of the magnetic tape),
The direction (or presence or absence) of the phase shift is reversed from the original.

Originally, the overlap period was provided so that signal dropout would not occur even if the above-mentioned switching phase of the logic signal is shifted between recording and reproduction. However, when the chromaticity signal deviates, a period occurs during reproduction in which the direction of the phase shift (or its presence or absence) is opposite to that known from the level of the logic signal. During this period, there were problems such as not only no color being applied, but also disturbances to the APC of the reproduced chromaticity signal circuit, causing flicker in the upper part of the image.

Therefore, in order to avoid this problem, it is possible to prepare two recording signal circuits and supply signals to the two video heads separately, but this poses a problem in terms of cost, and the camera integrated V
There are mounting problems in devices such as TRs that require compactness and weight reduction.

By the way, the above-mentioned 2 heads wrapped 180 degrees is a type of VTR.
Since the rotary head drum has a large diameter, it is not suitable for devices that require compactness and weight reduction, such as a camera-integrated VTR. Therefore, the conventional method was to create the same recording pattern as a normal two-head 180-degree VTR to ensure compatibility, and then reduce the diameter of the rotating head drum to about 60%.
This is described in Japanese Patent Publication No. 60-51306. In other words, magnetic tape is wrapped around the drum at over 300 degrees,
In this method, two video heads with opposite azimuths are mounted very close to each other and the head drum is rotated one field to record.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a magnetic recording device that does not disturb the reproduction APC circuit and is suitable for downsizing and weight reduction.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a magnetic tape is wound around the outer peripheral surface at a predetermined angle smaller than 360 degrees, and the magnetic tape is wound at a rate of one rotation in a period corresponding to one field of a video signal. A rotary head drum that rotates around a rotation axis, and a head gap having a different azimuth angle from each other, close to each other within a predetermined distance on the outer periphery of the rotary head drum, and located at approximately the same position in the direction of the rotation axis. a pair of video heads that operate on the magnetic tape by rotating in accordance with the rotation of the rotary head drum; In a magnetic recording apparatus that records the video signal on the magnetic tape by the video head, the video signal is input alternately to a pair of video heads for each field, and when the video signal to be recorded is compressed on the time axis. Of these, for the low-pass conversion chromaticity signal, low-pass conversion is performed in each field such that the phase shift is continuous with the phase shift within the field before the start point and after the end point of the field, respectively. The time axis is compressed while adding the chromaticity signal for several horizontal periods.

In addition, if necessary, when multiplexing a tracking control pilot signal used for tracking control during playback onto the video signal to be recorded, the time-axis compressed video signal may be multiplexed in l-field units, respectively. Multiplexing is performed so that a tracking control pilot signal whose frequency is the same as the frequency within the field is added before the start point and after the end point of the field.

[Effect]

With the above configuration, the direction (or presence or absence) of the phase shift of the low-pass conversion chromaticity signal is generally the same within the - recording track, including the overlap recording period, and the APC of the chromaticity signal circuit is disturbed during playback. will no longer be given.

Also, for the pilot signal for tracking control,
- The frequencies are the same within the recording track of the book, including the overlap period, and no disturbance is caused to the tracking control circuit during reproduction.

These effects can be obtained without preparing two circuit systems.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 4 is a plan view of the vicinity of the rotary head drum used in the present invention.

A magnetic tape 4 positioned by inclined pins 7A, 7B is wound around the entire circumference of the rotary head drum 6, and video heads 8A, 4 having different azimuths are wound around the rotary head drum 6.
8B are mounted very close together and at the same height. The rotating head drum 6 rotates once in one field, and the video head 8
A and 8B are given recording signals alternately every rotation. In this way, it is possible to leave on the magnetic tape 4 the same recording pattern as that of a VTR with two heads wrapped 180 degrees.

In other words, in terms of mechanism, the
This is similar to that described in Publication No. 306.

Ideally, the magnetic tape 4 should be wrapped 360 degrees around the rotating head drum 6.
The diameter of the two heads can be wrapped around 180 degrees, making it about 1 in the shape. However, in reality, the magnetic tape 4 must be automatically loaded from within the cassette, so it can only be wound around 330 degrees. It is not possible to record the signal while it is passing through. Therefore, in order to avoid this period, it is necessary to time-domain the signal in units of one field before recording.

FIG. 5 is a time chart roughly showing how time is compressed during recording. Continuous input signals as shown in figure (a) are processed in one field (V in the figure) using a semiconductor memory.
) is compressed by k (<1) times in units of azimuths, and the timing at which the signal is absent is alternately applied to both azimuth heads as an intermittent signal as shown in Fig. 4 (b), and the video shown in Fig. 4. It is sufficient to match the timing at which the heads 8A and 8B pass through the angle section.The period for recording 1 field is designed to correspond to an angle of 300 degrees in the rotating head drum 6 shown in FIG. This is realistic, and in this case k=360''6.

Assume that the recording track on the magnetic tape 4 when the signal shown in FIG. 5(b) is recorded becomes 1. as shown in FIG. 6(a). Here, 9A and 9B are recording tracks by the video heads 8A and 8B, respectively. Assume that the range indicated by K[ is the period of 300 degrees above! If so, this is 180 from M to N in Figure 3 above.
corresponds to a period of 30 degrees. Therefore, the overlapping period outside of that (at the end of the magnetic tape) in FIG. 3 no longer exists. In FIG. 4, video heads 8A, 8
This is unavoidable since it is impossible for B to be located at the upper and lower ends of the magnetic tape 4 at the same time. but,
If this continues, as mentioned above, there is a risk that part of the signal will be lost during playback. Therefore, when performing the above-described time axis compression operation, a signal is added for a short time (about 5 horizontal periods) before and after the time kV shown in FIG.
) It is necessary to form recording tracks IOA and IOB having an overlapping period as shown by the hatched area.

The main point of the present invention is the method of forming this overlap period. In particular, the phase shift of the chromaticity signal is made the same within the same recording track, including the overlap period, in order to eliminate factors that cause APC disturbance during reproduction.

To achieve this, in order to compress the time axis of the recorded chromaticity signal that has been subjected to low frequency conversion and phase shift, it is necessary to store the recorded chromaticity signal in the semiconductor memory, and when reading it out, to combine the signals within the same field (with the same phase shift). It is only necessary to cut out the 7th part and add it before and after it so that the phase shift is continuous.
This will be explained using the diagram and FIG. These diagrams schematically show the phase shift direction of the chromaticity signal.

Here, we will discuss a case in which the head with one azimuth angle of each piece does not shift the phase, and the head with the remaining azimuth angle inverts the phase every IH (horizontal period) to record, and in particular, the signal recorded by the latter head. The process is illustrated.

FIG. 7 shows the vicinity of the starting point of a recording track. M in FIG. 1 means that recording is performed at M in FIG. 6. Also, the arrow indicates the direction of phase shift, i.e. 1)(
It is inverted (shifted by 180'') every (horizontal period).

When compressing the time axis, simply storing it in a semiconductor memory and reading it out using a clock with a higher frequency (for example, one time) than the clock at which it was stored results in an M
It is not possible to form an overlapping period earlier than . Therefore, by reading out and inserting signals separated by <2nH (n is an integer) in advance as shown in FIG. 7(b), the intended purpose is to obtain a signal with a continuous overlap period of phase shift. be able to. The signal used for insertion will be read twice from the semiconductor memory.

FIG. 7(b) shows the case where n is 3, but of course the case is not limited to this. Also, the signals in the overlap period do not need to be arranged in the order of the lines, and the point is that the phase shift is continuous. It's fine as long as you can maintain your sexuality.

8(a) and 8(b), similar to FIGS. 7(a) and 7(b), show a method of generating an overlap period near the end point n of a recording track. Again, it is sufficient to read two volumes of signals separated by 2 nH and create them.

The number of scanning lines in one field is 262.5 in NTSC, so it is impossible for the number between M and N to be an integral multiple of IH, but in Figures 7 and 8, we prioritized ease of understanding. These are shown as being at the boundary of one horizontal period.

Note that for the signals recorded by the remaining one head without phase shift, any signal within that field may be used to create the overlap period. Actually, for convenience of memory control, it is easy to use signals separated by 2 nH as above.

As another example, if both azimuth heads shift the phase by 90" per horizontal opening period in opposite directions, the signal recorded by either head will overlap with a signal that is 4 nH apart. All you have to do is create a wrap period.

In the above method, at the time of recording and at the time of playback.

When the switching phase of the logic signal indicating the rotational phase of the rotary head drum is shifted, the overlap period signal generated as described above appears as a reproduction signal.

Although some of the image information in the vertical direction is discontinuous, there is no practical problem because it is located at the bottom of the TV screen, in the overscan range. Rather, the effect of maintaining the continuity of phase shift and eliminating factors that disturb APC during reproduction is significant.

The operation of the entire device using the above items will be described.

FIG. 1 is a block diagram showing a magnetic recording device as an embodiment of the present invention. - As an example, the case will be explained based on the NTSC 8mm video standard.

11A, IIB, 27 are input terminals of the device,
A luminance signal, two chromaticity signals, and an audio signal are input in this order. 11
The luminance signal from A is AGC (Aut.

matic Galn Control) circuit 12
After setting the amplitude (usually the amplitude of the synchronization signal) to be constant,
LPF (Low Pa5s Filter) 1
Bandwidth is limited by 5. This LPF 15 also acts as a filter for the time base compression circuit 19 using a semiconductor memory in the subsequent stage. The output of the above AGC circuit 12 is also given to the adder 13 at the same time, where it is added with the chromaticity signal from the input terminal 11B, and then output to the output terminal 14 and displayed on an external monitor TV (or viewfinder). Enables you to monitor the image being recorded.

The output of LPF15 is sent to synchronous separation circuit 17 and clamp circuit 1.
Sent to 6. In the latter case, the synchronization tip of the luminance signal is clamped to a constant DC level based on the timing of the synchronization pulse from the synchronization separation circuit 17.

The output of the clamp circuit 16 is connected to the time axis compression circuit 19 and the AGC.
The signal is applied to the detection circuit 18. The latter is also given the previous synchronization pulse, and controls the gain of the AGC circuit 12 so that the level of the signal (usually a synchronization signal) is constant.

On the other hand, the time axis compression circuit 19 compresses the time axis so as to avoid periods during which the video heads 8A, 8B are not in contact with the magnetic tape 4 (for example, to i for each field). After that, the pre-emphasis circuit 20 reproduces the S/
The high frequency band is emphasized to improve N, the FM modulator 21 outputs a specified FM modulation signal, and the HPF 22 converts the low frequency band (approximately 1.5
MHz) components are removed and added to the adder 35.

Here, a chromaticity signal, an audio signal, and a pilot signal, which will be described later, are added to a band of 1.5 MHz or less, and then amplified by a recording amplifier 36. , two video heads 8A
(+azimuth) and 8B (-azimuth) are recorded on the magnetic tape 4.

As described above, the video heads 8A and 8B are mounted on a rotating head drum (not shown).

A tack pulse generator 38 is attached to this head drum to generate a pulse per revolution to inform the rotational phase. This tack pulse is used to obtain a logic signal whose level changes every branch circuit yield period.

If the switch 37 is driven using this, the desired operation can be obtained.

Next, the chromaticity signal from the previous input terminal 11B is
After being band-limited at 23, the signal is input to a chromaticity signal recording processing circuit 24. Here, the burst level is set to a constant value by A CC (A utoa+atic ChromaC).
ontrol) and burst emphasis that emphasizes the burst level by 6 dB. In addition, according to the output logic signal of the frequency dividing circuit 39, frequency low-frequency conversion is performed while performing a phase shift corresponding to the azimuth of the recording video head, and sideband waves are nonlinearly emphasized with respect to subcarrier waves. Chroma emphasis is applied. After that, LP
At F25, high frequency components accompanying the above low frequency conversion are removed. Note that this LPF 25 has the following effects on the next stage time compression circuit 26:
It also acts as a filter.

As described above, the time axis compression circuit 26 compresses the time axis of the signal in units of one field while adding continuous overlap periods of phase shifts, and then the adder 3
Give to 5.

In addition, the audio signal from the previous input terminal 27 is fed as is to the output terminal 28 so that the audio to be recorded can be monitored externally, and high frequencies are non-linearly emphasized to improve the playback S/N. 6 then applied to the noise reduction circuit 29.

The LPF 30 removes out-of-band components (also acts as a filter), and the time-base compression circuit 31 receives a time-base compression effect as described later. Furthermore, the FM modulator 32 converts the signal into a specified FM modulation signal, the BPF 33 removes unnecessary high-order sidebands, and the signal is then added to the adder 35.

Further, the pilot generation circuit 34 generates a pilot signal for tracking control during reproduction based on the output logic signal of the frequency dividing circuit 39. For example, in the 8mm video standard, -fH (+azimuth), 50
fH (-azimuth).

"2hi if, (+azimuth), upper f, (-azimuth) (
f, is supposed to cycle through the frequencies in the order of horizontal synchronization frequency), but here, it is generated at a frequency that is higher (for example, twice as high) as the compression weight of the previous signal, and is given to the adder 35. .

Next, the memory controller 40 controls the addresses of the semiconductor memories forming the time axis compression circuits 19, 26, and 31 based on the synchronization pulse, the output logic signal of the frequency dividing circuit 39, and the like. As described above, the chromaticity signal compression circuit 26 is configured to add and compress signals with continuous phase shifts during the overlap period. The same address control is applied to the brightness signal compression circuit 19 so that the brightness signal is compressed with an overlap period. In the audio signal compression JI31, unlike the luminance/chromaticity signals,
Since it is not possible to form an overlap period using signals with different timings (if there is a phase shift between the above logic signals during recording and playback, noise with a period of 60H will be generated). Add using a signal with the same timing as recorded.

Note that with the configuration shown in FIG. 1, all pilot signals having the same frequency are recorded in one recording track including the overlap period. In the case of the conventional two-head 180 degree winding, M and N are located on the edge side of the magnetic tape from points M and N in Figure 3 in the recording track.
The signal had to have a different frequency (same frequency as the adjacent track) than the 180 degree section between the tracks. Therefore, if there is a phase shift between the above logic signals during recording and playback,
- There was a risk that the tracking servo would be disturbed during instantaneous playback, but this embodiment can also eliminate this problem.

In addition, by slightly modifying Fig. 1 and making it as shown in Fig. 9, the pilot signal generation circuit 41 generates a signal with a frequency according to the 8 mm video standard, and the adder 42 adds it to the chromaticity signal before time axis compression. It goes without saying that similar effects can be obtained even with a configuration in which:

B Furthermore, it is not limited to 8mm video, for example, V
It can also be applied to those of H5 standard. At that time, there is no need to generate a pilot signal, and audio FM modulation recording is no longer essential, and no essential changes are required.

〔Effect of the invention〕

According to the present invention, in a helical scan type VTR,
- It is possible to match the phase shift direction (or presence or absence) of the low frequency conversion chromaticity signal at all locations in the recording track of the book, including the overlap period. For this reason,
Even if the switching phase of the logic signal generated from the tack pulse during recording and playback is shifted by 1, it will not disturb the APC circuit of the 1 chromaticity signal during playback, and the cause of flicker at the top of the screen can be eliminated. .

In addition, in the case where a pilot signal is used for playback tracking control, the pilot signal frequency can be made to match all over one recording track, including the overlap period. This has the effect of eliminating factors that disturb tracking control.

The above effects can be obtained without using two circuits, and it can also contribute to making the device smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a magnetic recording device as an embodiment of the present invention, FIG. 2 is a plan view showing the vicinity of a rotary head drum in a conventional magnetic recording and reproducing device, and FIG. 3 is a video head of FIG. 2. FIG. 4 is a plan view showing the vicinity of the rotary head drum used in the present invention, FIG. 5 is a time chart for explaining the time compression method used in the present invention, and FIG. The figure is an explanatory diagram showing the recording pattern on the magnetic tape by the video head of FIG. 4, and FIGS. 7 and 8 are explanatory diagrams for explaining the overlap period generation method of the low-pass conversion chromaticity signal in the present invention, respectively. FIG. 9 is a block diagram showing a modification of the embodiment shown in FIG. 1. 19.26.31... Time axis compression circuit, 24... Chromaticity signal recording processing circuit, 40... Memory controller,
34.41...Pilot signal generation circuit. Figure 2 Figure 3 Figure 5 + Figure 5 Figure V; Directional lock Figure 6 Figure 7 (OL) Figure 8 (α)

Claims (1)

[Claims] 1. A magnetic tape is wound around the outer circumferential surface over a predetermined angle smaller than 360 degrees, and the magnetic tape is wound around the rotation axis at a rate of one rotation in a period corresponding to one field of a video signal. The rotating head drums have different azimuth angles of head gaps, and are attached to the outer periphery of the rotating head drums so as to be close to each other within a predetermined distance and at approximately the same position in the direction of the rotation axis, a pair of video heads that scan the magnetic tape by rotating in accordance with the rotation of the rotary head drum; , in a magnetic recording device which records data on the magnetic tape by the video heads alternately, when compressing the time axis of the video signal to be recorded, the low frequency of the video signal is Regarding the converted chromaticity signal, for each field, count the number of low-pass converted chromaticity signals whose phase shift is continuous with the phase shift within the field, respectively, before the start point and after the end point of the field. A magnetic recording device characterized by compressing the time axis while adding horizontal periods. 2. In the magnetic recording apparatus according to claim 1, when a tracking control pilot signal used for tracking control during playback is multiplexed on the video signal to be recorded, the time-axis compressed video signal is It is characterized in that it is multiplexed in such a way that a tracking control pilot signal whose frequency is the same as the frequency within that field is added before the start point and after the end point of each field in each field. magnetic recording device.