JPH0752489B2 - Magnetic recording / reproducing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a helical scan type magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus using different magnetic head pairs in a standard mode and a long time mode. .

[Conventional technology]

In the helical scan type magnetic recording / reproducing apparatus,
It is known that different magnetic head pairs are used in the standard mode and the long time mode in which recording and reproduction are performed by slowing the running speed of the magnetic tape. These magnetic head pairs consist of two magnetic heads having different azimuth angles, and are arranged on the rotary cylinder at angular intervals of 180 °. This makes it possible to adopt a so-called azimuth recording method in which the magnetization directions are different between adjacent tracks on the magnetic tape in both the standard and long time modes.

By the way, such a magnetic recording / reproducing apparatus generally enables variable speed reproduction in which the magnetic tape is run at a speed different from that at the time of recording for reproduction. In such a variable speed reproduction mode, since the trace pattern of each magnetic head is different from that at the time of recording, a noise bar is generally generated on the screen. Conventionally, various means have been proposed for a screen having a small number of noise bars. As one example, a method for obtaining a good image in a high speed reproduction state is described in Japanese Patent Laid-Open No. 58-83490. This is one in which one magnetic head having a different azimuth angle for the standard mode and one magnetic head having a different azimuth angle for the long time mode are arranged close to each other to form a head pair (hereinafter referred to as a double azimuth head pair). It is like obtaining an image without a noise bar by using two pairs and selecting a head having a large reproduction output among the four magnetic heads in a high-speed reproduction state.

Here, this conventional technique will be specifically described with reference to the drawings.

FIG. 5 shows the rotary cylinder, where 1 is a rotary cylinder and 1a to 1d are magnetic heads.

In the figure, the magnetic heads 1a and 1b are for the long-time mode and have different azimuth angles. In the figure, in order to show these azimuth angles, a symbol is attached to the magnetic head 1a and a symbol is attached to the magnetic head 1b. The magnetic heads 1c and 1d are for the standard mode, and the azimuth angles are different between them. And the magnetic head 1c has a symbol,
A symbol is attached to the magnetic head 1d. Magnetic head 1a, 1b
And the magnetic heads 1c and 1d are arranged at an angular interval of 180 °, respectively.In addition, the magnetic head 1a for the long mode and the magnetic head 1c for the standard mode having a different azimuth angle from the magnetic head 1a.
And 2H of the video signal on the magnetic tape (1H is 1
(Horizontal period) are arranged close to each other at an interval of recording length (740 mm) to form a pair of double azimuth heads,
Long-time mode magnetic head 1b and standard mode magnetic head
1d is also a double azimuth head pair.

Here, the head width of the magnetic head 1c for standard mode is 40μ.
Similarly, the head width of the magnetic head 1d is set to 58 μm, and the head widths of the magnetic heads 1a and 1b for the long time mode are both set to 30 μm.

FIG. 6 shows a track pattern on a magnetic tape formed by using the cylinder shown in FIG. 5, where FIG. 6 (a) shows a standard mode recording pattern and FIG. 6 (b) shows a long time mode. It is a recording pattern. 6th in standard mode
As shown in FIG. 5A, tracks of 58 μm width and tracks of 40 μm width are alternately formed, and a guard band of 18 μm width is generated between the 40 μm width track and the next 58 μm width track. On the other hand, in the long time mode, 19μ
Tracks of m width are sequentially formed without a guard band.

Now, when the magnetic tape is run at a higher speed than at the time of recording, the inclination of the head running locus is different from that at the time of recording, and the head traverses a number of tracks corresponding to the speed. Since the azimuths are alternately recorded on the magnetic tape, the reproduction signal can be obtained only intermittently, and some bar noises are generated on the screen. In the long-time recording mode of FIG. 6 (b), since the head width is wider than the track width, only a thin bar noise appears, but in the standard recording mode of FIG. 6 (a), the track width Since the head width is narrower than 58 μm and there is a guard band on the pattern, wide bar noise appears on the screen.

In such a conventional technique, the high-speed reproduced image in the standard mode is improved as follows. For example, forward direction 3
The running path of the magnetic head when the magnetic tape is run at double speed is shown in FIG. Magnetic head 1
CH1 is the pair of double azimuth heads for a and 1c, and CH2 is the pair of double azimuth heads for magnetic heads 1b and 1d.
Then, when the magnetic tape runs and the rotary cylinder 1 rotates, the double azimuth head pair scans the magnetic tape alternately with CH1 and CH2 every half rotation of the rotary cylinder, but the double azimuth head pair of CH1 When scanning a magnetic tape, one of the magnetic heads 1a, 1c produces a large reproduction output according to the state in which the magnetic tape scans a track on the magnetic tape, and the CH2 double azimuth head pair scans the magnetic tape. Sometimes, in the same way, magnetic head 1
Either b or 1d has a high playback output.

Therefore, by selecting the magnetic head having the largest reproduction output among these magnetic heads 1a to 1d, a continuous reproduction signal can be obtained. This is shown in FIG. The figure (a) shows the envelope of the azimuth head output, and the figure (b) shows the envelope of the azimuth head output. As described above, since FIGS. 8A and 8B are in a complementary relationship, by performing envelope detection and selecting the magnetic head having the larger output, as shown in FIG. The reproduced signal thus obtained is obtained.

The reason why the head widths of the standard mode magnetic heads 1c and 1d are different is as follows.

In the standard mode, the running speed of the magnetic tape is made faster than in the long-time mode to make the track width wider, and the reproduction output is increased to increase the S / N of the video signal. Therefore, the head widths of the magnetic heads 1c and 1d are made wider than the head widths of the long-time mode magnetic heads 1a and 1b.

By the way, when performing still or slow reproduction, since the azimuth recording method is adopted and the running locus of the magnetic head does not coincide with the track, using only the magnetic head for the same mode causes a noise bar. For this reason, still slow reproduction is performed using magnetic heads for different modes, but especially when performing slow slow reproduction using a magnetic tape recorded in a long time mode,
When the standard mode magnetic head is used in addition to the long-time mode magnetic head, if the two standard mode magnetic heads both have a head width of 58 μm, the track width in the standard mode is constant at 58 μm and the guard band However, when scanning a magnetic tape on which tracks are formed in the long-time mode, the standard-mode magnetic head also reproduces adjacent tracks in the same magnetization direction. The head width of 58 μm is about 3 times the track width of 19 μm). For this reason, the crosstalk becomes large and the quality of the reproduced image is significantly deteriorated.

Therefore, one head width of the standard mode magnetic head is
Image quality deterioration in standard playback mode is small, and even when used for slow still playback in long-time mode, the size is reduced to such an extent that it will straddle adjacent tracks, and this standard-mode magnetic head will be used for a long time. It is designed to be used for slow still playback in mode. Therefore, as mentioned above, the head width of the standard mode magnetic head 1d is 58μ.
The head width of the magnetic head 1c is set to 40 μm, which is narrower than that of the magnetic head 1c.

[Problems to be solved by the invention]

In the helical scan type magnetic recording / reproducing apparatus,
Even in the playback mode, there are normal playback that makes the running speed of the magnetic tape the same as during recording and variable speed playback that makes the running speed of the magnetic tape different during recording. There is still high speed reproduction, and these are as follows by specifying the magnetic head to be used.
A reproduced image of good quality with few noise bars can be obtained.

By the way, during a transition of the reproduction mode switching, such as switching from normal reproduction to slow reproduction, conventionally, a magnetic head to be used is generally selected according to the next reproduction mode. . However,
During such a transition, the running locus of the magnetic head on the track in the reproducing mode, which has been performed so far, changes to the running locus in the reproducing mode, which should be performed next. This is different from the playback mode of, and large or many noise bars will appear.

An object of the present invention is to solve the above problems and to reduce a magnetic recording / reproducing apparatus capable of reducing a noise bar during a transition of a reproducing mode.

[Means for solving problems]

In order to achieve the above object, the present invention detects a reproduction mode switching time point from a reproduction mode switching signal and selects a magnetic head having the largest reproduction output among four magnetic heads for a certain period from the switching time point.

[Action]

A certain period from the time of switching the reproduction mode is a transition period of the reproduction mode. In this period, no matter how each magnetic head scans a track on the magnetic tape, one of them is always The track is playing and scanning fairly well. Therefore, by selecting the magnetic head having the maximum reproduction output from the four magnetic heads, a continuous reproduction signal can be obtained and a reproduction image with reduced noise bars can be obtained.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention. 1a to 1d are magnetic heads shown in FIG. 5, 2a to 2d are amplifiers, 3 to 5 are changeover switches, and 6 , 7 is an amplitude detector, 8 is a comparator, 9 is an amplifier, 10 is a luminance / color processing circuit, 11 is a logic circuit, 12 is a mode change determination circuit, and 13 is a system controller.

In the figure, the magnetic heads 1a to 1d are arranged on the rotary cylinder 1 in the same plane as shown in FIG.
The a and 1b are for long time mode, and the magnetic heads 1c and 1d are for standard mode. The changeover switches 3 and 4 are controlled by a 30 Hz switch pulse SW30 synchronized with the rotation phase of the rotary cylinder 1, and during the half rotation period of the rotary cylinder 1 in which the magnetic heads 1a and 1c scan the magnetic tape, the changeover switch 3 is turned on. Magnetic head
During the half rotation period of the rotary cylinder 1 in which the changeover switch 4 selects the magnetic head 1c side and the magnetic heads 1b and 1d scan the magnetic tape, the changeover switch 3 selects the magnetic head 1a.
The changeover switch 4 selects the magnetic head 1d side on the 1b side.

The head width of the magnetic heads 1c and 1d for standard mode is 48 μm,
Head width of magnetic heads 1a and 1b for long time mode is 30μm
Is. At the time of standard recording, the magnetic tape runs at the same speed as the conventional magnetic recording / reproducing apparatus, and as shown in FIG. 2 (a), tracks are formed on the magnetic tape at a track pitch of 58 μm and a track width of 48 μm. 10μ between tracks
A guard band of m width is formed. Further, in the long-time recording mode, each track is formed with a track width of 19 μm and no guard band, as in the prior art shown in FIG. 6 (b).

In FIG. 1, the changeover switch 5 is switch-controlled by the logic circuit 11 in accordance with the reproduction mode. The reproduction signal selected by the changeover switch 3 is detected by the amplitude detector 6,
The reproduction signal selected by the changeover switch 4 is detected by the amplitude detector 7, and the detection outputs of these amplitude detectors 6, 7 are compared by the comparator 8. Comparison output A of this comparator 8
Has a level representing the larger amplitude of the reproduction signals selected by the changeover switches 3 and 4, and is always supplied to the logic circuit 11 in the reproduction mode. The reproduction signal selected by the changeover switch 5 is amplified by the amplifier 9 and then supplied to the luminance / color processing circuit 10.

On the other hand, the system controller 13 outputs the mode signal B representing the reproduction mode and the mode switching pulse C representing the switching point of the reproduction mode, and the mode change determination circuit 12
With this mode switching pulse C, a determination pulse D having a constant time width is formed and output from the time of switching the reproduction mode.
The time width (pulse width) of the determination pulse D is the period from the running locus of the magnetic head in the reproducing mode, which has been performed so far, to the running locus of the magnetic head in the reproducing mode, which is to be performed next (that is, reproduction). It is set slightly longer than the mode transition period).

The logic circuit 11 forms the changeover control signal of the changeover switch 5 by using the mode signal B and the comparison output A according to the designated reproduction mode. The judgment pulse D is supplied,
Of the reproduction signals selected by the pulse period change-over switches 3 and 4 of the judgment pulse D, the change-over switch 5 selects the reproduction signal having the larger amplitude. Here, since the changeover switches 3 and 4 are changed over every half rotation of the rotary cylinder 1, when the double azimuth head pair of the magnetic heads 1a and 1c is scanning the magnetic tape, the reproduction output of them is large. One is selected by the changeover switch 5, and the magnetic head
When the pair of double azimuth heads 1b and 1d is scanning the magnetic tape, the one with the larger reproduction output is selected, and in the end, the magnetic heads 1a to 1d are selected in the transient period of the reproduction mode. All of them are used, and the one with the largest reproduction output is always selected.

Here, magnetic head 1a → EPCH1 magnetic head 1b → EPCH2 magnetic head 1c → SPCH2 magnetic head 1d → SPCH1 The following table shows the magnetic heads used in the recording mode and each reproducing mode.

The above contents will be described below with reference to the operation of the changeover switch 5.

During recording and normal reproduction, the selector switch 5 is closed to the Y side in the standard mode and to the X side in the long time mode.

In still reproduction in the standard mode, when the magnetic heads 1a and 1b scan the magnetic tape, the changeover switch 3 is set to the b side.
The magnetic switch 1b (EPCH2) with the changeover switch 5 closed to the X side
When the magnetic heads c and 1d scan the magnetic tape, the changeover switch 4 is closed to the side a and the changeover switch 5 is closed to the side Y to select the reproduction signal of the magnetic head 1c (SPCH2). Similarly, at the time of still reproduction in the long time mode, the half rotation period changeover switch 3 of the rotary cylinder 1 is set to a.
To the magnetic head 1a (EP
CH1) reproduction signal is selected, and the other half rotation period changeover switch 4 of the rotary cylinder 1 is closed to the b side and the changeover switch 5 is closed to the Y side to select the reproduction signal of the magnetic head 1d (SPCH1).

Thus, during still reproduction, the same track is repeatedly reproduced and scanned by the magnetic head having the same azimuth angle. Since the magnetic heads 1a and 1b have the same head width, the magnetic heads to be used may be the same during still reproduction in either standard or long mode.

Slow reproduction is performed by running a magnetic tape intermittently and alternately performing normal reproduction and still reproduction. Therefore, the change-over switches 3, 4 and 5 alternately perform the magnetic head selection operation during normal reproduction and the magnetic head selection operation during still reproduction, respectively.

In the case of search reproduction, since the scanning locus of the magnetic head extends over many tracks, the changeover switches 3 to 5 perform the same operation as in the transient period of the reproduction mode.

Therefore, when the current reproduction mode is the normal reproduction mode and the still reproduction mode is instructed next for the magnetic tape having the tracks formed in the standard mode, the system controller 13 instructs the logic circuit 11 to reproduce the still reproduction mode. Mode signal B is supplied to the logic circuit 11 from the mode change judgment circuit 12 for a certain period of time. Therefore, the mode change determination circuit 12 controls the changeover switch 5 as described above during the period when the determination signal D is supplied, and the maximum reproduction signal is selected from the reproduction signals of the magnetic heads 1a to 1d and the amplifier 9 is selected. Is supplied to. When the determination signal D ends, the mode signal B controls the changeover switch 5 as described above to perform still reproduction.

As described above, in this embodiment, a large reproduction output is always obtained continuously even during the transition period of the reproduction mode, and a high-quality reproduced image in which the noise bar is significantly reduced can be obtained.

FIG. 3 is a block diagram showing a specific example of the mode change determination circuit 12 in FIG. 1, in which 13a and 13b are input terminals and 14a.
-14d is a mono multivibrator, 15 is an OR circuit, and 16 is a mono multivibrator. Further, FIG. 4 is a timing chart showing the operation of this specific example, and the signals corresponding to those of FIG. 3 are designated by the same reference numerals.

In FIG. 3 and FIG. 4, when the current reproduction mode is the normal reproduction mode and the search reproduction is instructed and the input signal C ₁ of the input terminal 13a changes from the low level to the high level (time
t ₁ ), on its rising edge the mono multivibrator 14a
Is triggered, and a narrow, high-level Q output representing the rising edge of the input signal C ₁ (at the start of search reproduction) is obtained. This Q output is supplied to the mono multivibrator 16 via the OR circuit 15. This triggers the mono multivibrator 16 to obtain the Q output representing the transient period of the reproduction mode as the determination signal D. When the input signal C ₁ changes from the high level to the low level (time t ₂ ) due to the search playback end command, the mono-multivibrator 14b is triggered by the falling edge of the input signal C _{1 and} the falling edge of the input signal C ₁ (that is, the search A Q output representing the time point (at which the reproduction is switched to the normal reproduction) is obtained. This Q output is an OR circuit
The signal is supplied to the mono multivibrator 16 via 15, and the mono multivibrator 16 is triggered to obtain the determination signal D.

The same applies when performing slow playback, and input terminal 13
b input signal C ₂ of the rising edge of the mono multivibrator 14c on the falling edge, 14d is triggered, the determination signal D is obtained is monostable multivibrator 16 is triggered by future Q output.

Similarly for still reproduction, a mono-multivibrator for detecting rising and falling edges of the input signal may be provided, and these Q outputs may be supplied to the mono-multivibrator 16 via the OR circuit 15.

In this specific example, the variable speed reproductions of still, slow, and search are set through the normal reproduction, and when these are completed, the normal reproduction is started, but the present invention is not limited to this.

〔The invention's effect〕

As described above, according to the present invention, even in the transient period of the reproducing mode, the largest reproducing signal is selected from all the reproducing signals of the magnetic heads provided, so that continuous reproducing signals are selected. And a reproduced image of high quality with reduced noise bars can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, FIG. 2 is a track pattern diagram on a magnetic tape in a standard mode and a long time mode, and FIG. 3 is a mode change in FIG. FIG. 4 is a block diagram showing a specific example of the judgment circuit, FIG. 4 is a timing chart showing the operation of this specific example, FIG. 5 is a plan view showing a rotary cylinder, and FIG. 6 is a magnetic tape on a conventional magnetic recording / reproducing apparatus. FIG. 7 is a pattern diagram showing the scanning locus of the magnetic head during variable speed reproduction, and FIG. 8 is a waveform diagram showing the reproduction signal of each magnetic head according to the scanning locus of FIG. 1a to 1d ... Magnetic head, 3 to 5 ... Switching head, 6,7 ...
Amplitude detector, 8 Comparator, 11 Logic circuit, 12 Mode change judgment circuit, 13 System controller.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04N 5/7826 5/93

Claims (1)

[Claims] 1. A first double azimuth head pair in which two magnetic heads having different azimuth angles are arranged in the vicinity of a rotating cylinder, and a rotating double cylinder with respect to the first double azimuth head pair. A magnetic recording / reproducing apparatus having a second double azimuth head pair in which two magnetic heads arranged at an angular interval of ° and different in azimuth angle are arranged in close proximity to each other, wherein the first and second double azimuth heads Inputting signals from four magnetic heads of a pair, and outputting two signals from two magnetic heads of a double azimuth head pair scanning the magnetic tape among the first and second double azimuth head pairs A first switch means that is switched so as to switch between the two signals from the first switch means, and a comparing means that determines and compares the larger one of the two signals from the first switch means; Detection means for detecting a fixed period from the time when the reproduction mode is switched by the mode switching signal, second switch means for switching and outputting two signals from the first switch means, and detection by the detection means And a control means for controlling the second switch means so as to output the signal on the side determined by the comparison means for a predetermined period of time. Based on the signal from the second switch means, A magnetic recording / reproducing apparatus, which produces a reproduced image in a transition period of a reproducing mode.