JPH06209446A - Variable speed reproduction method for magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To suppress appearance of noise bars in the variable speed reproduction state, to increase a multiple of variable speed and to reduce a defect of picture elements in a reproduced picture. CONSTITUTION:Picture information is obtained from plural tracks included for one scanning period by alternately executing the operation of a magnetic head 3 to trace a track 2 of a prescribed tape 1 and the operation of moving the head to a track of the same azimuth apart by at least one track from the track traced at present during one scanning period in the variable reproduction state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable speed reproducing method for a magnetic recording / reproducing apparatus in which a magnetic head follows a track to obtain a maximum reproduction output signal.

[0002]

2. Description of the Related Art In recent years, in VTRs (video tape recorders), the density of recording signals has been increasing, and the track is becoming narrower accordingly. However, when the track width becomes narrow, track deviation easily occurs. Track deviation is
It is caused by the difference between the recorded track and the scanning locus of the magnetic head at the time of reproduction, and is particularly likely to occur when a tape recorded by another model is reproduced. Due to the track shift, a sufficient reproduction output cannot be obtained.

As described above, there is a dynamic tracking technique of displacing a magnetic head having a tracking deviation in the track width direction by an actuator to bring it into a normal tracking state. Commonly known dynamic tracking functions include a 4-frequency pilot method, an envelope detection method, and a dither method. All of these methods are the same in that the relative position (error) between the track and the magnetic head is detected, and the head actuator is driven accordingly to bring the error close to zero. As a head actuator that realizes this tracking function, a piezoelectric element, a voice coil motor or the like is generally used.

FIG. 8 is a diagram showing a configuration around a magnetic head for realizing such a dynamic tracking function. Referring to FIG. 8, magnetic head 3 includes a + azimuth A head and a −azimuth B head. The A head and the B head are provided on the actuator 80, respectively. The actuator 80 is a rotary track 50.
Are provided at positions opposite to each other by 180 degrees.

In operation, the head actuator 80
Is displaced in response to a signal V which detects a relative error between the track and the magnetic head, and causes the magnetic head 3 to follow the track. Thereby, the tracking operation described above can be performed.

In the helical scan type VTR, when the magnetic head is immovable in the track width direction during variable speed reproduction, an angle is formed between the track of the magnetic head and the track. Scanning is performed over a plurality of tracks in one scanning period. Since the magnetic head scans the track obliquely, the output of the magnetic head repeatedly increases and decreases.

FIG. 9 is a diagram showing a locus of a magnetic head at 5 × speed as an example of variable speed reproduction. FIG. 10 is a diagram showing the envelope reproduction output of the magnetic head when the magnetic head locus 5 shown in FIG. 9 is taken. The head width is 1.5 times the track width. Referring to FIG. 9, the A head starts scanning from the start end of the B0 track and ends scanning at the end of the B2 track. As the A head approaches the A1 track, the reproduction output gradually increases during the T1 period. When the A head covers the entire width of the track (time t1), the maximum output is obtained, and the output in the period T2 is constant. However, when the A head starts to deviate from the A1 track (time t2), the reproduction output gradually decreases (period t3) and reaches the minimum output at time t3. After time t3, the A2 track is started to be reproduced in addition to the A1 track. Therefore, the reproduction output is in a state in which the A1 track and the A2 track are mixed, and becomes noise until the time t4 when the magnetic head is separated from the A1 track. After time t4, only the A2 track is reproduced, and the reproduction output gradually increases during the period T3. After that, the output becomes maximum and constant during the period of T2,
Finally, the output during the period T1 decreases, and one scan by the A head ends at the end of the track B2 (time t).
7). Here, the reproducing head is switched to the B head.

At the time of reproducing the analog-recorded image signal, a portion where the output is reduced appears as a noise bar on the screen, and when reproducing the digitally recorded image data, the image data is lost.

In order to prevent the above noise bar from appearing during variable speed reproduction, the stroke width of the head actuator is enlarged and one track is reproduced per scanning period at every track number according to the double speed number during variable speed reproduction. There is a way. As an example, FIG. 11 shows a reproducing method at +5 times speed.

Referring to FIG. 11, reference numeral 4a shows a locus of the head center when the magnetic head is immovable in the track width direction, and 4b shows a head center when the magnetic head is variable in the track width direction. Shows the locus of.

In operation, first, the A head continuously reproduces from the start end to the end of the A1 track in one scanning period.
At this time, the A head is displaced in the width direction of the track 2 by the head actuator 80 (FIG. 8) so that the A head does not come off the A1 track, and the A head is made to follow the A1 track. When the A head finishes reproducing the A1 track, the reproducing head switches from the A head to the B head,
Playback starts from the beginning of the B3 track. After that, the reproduction is continued every four tracks in the same manner.

FIG. 12 shows the amount of displacement (stroke) of the magnetic head during one scanning period at this time. Referring to FIG.
The magnetic head is linearly displaced in one scan, and the stroke S1 is 4 × track pitch.

[0013]

Therefore, in the variable speed reproduction method shown in FIG. 11, the stroke becomes larger as the number of double speeds becomes larger. However, since the head actuator is composed of an element such as a bimorph that vibrates in a small movable range, there is a problem that it is not possible to take a very large speed number.

An object of the present invention is to provide a variable speed reproducing method capable of suppressing the appearance of noise bars and increasing the multiple speed ratio in a magnetic recording / reproducing apparatus having a tracking function.

Another object of the present invention is to provide a variable speed reproducing method capable of reducing loss of image data in one scanning period during variable speed reproduction in a magnetic recording / reproducing apparatus of a digital recording / reproducing system having a tracking function. It is to be.

[0016]

A variable speed reproducing method for a magnetic recording / reproducing apparatus according to the present invention is applied to a magnetic recording / reproducing apparatus having an actuator for displacing a magnetic head in a track width direction, and has the following features. That is, in response to the shift multiple setting signal that is set externally, the first for causing the magnetic head to follow a predetermined track among a plurality of tracks included in one scan period during one scan period during variable speed reproduction. And a second control signal for instantaneously operating from a predetermined track being tracked to the closest track of the same azimuth, are alternately generated, and the generated first and second control signals are generated. In response, the amount of displacement of the actuator is controlled to sequentially move the magnetic head to a plurality of tracks included in one scanning period so as to follow the destination track.

[0017]

According to the present invention described above, the magnetic head is caused to follow a certain track during the first period during variable speed reproduction, and the magnetic head is momentarily moved to the same azimuth track which is separated by one track pitch during the second period. Since it is moved, the signal is dropped only for a short period of time moving from one track to another. Therefore, when reproducing an image signal recorded by an analog method, it is possible to suppress the appearance of noise bars. Further, since the stroke is reduced as compared with the case where the magnetic head is moved at least one track pitch so as to follow one track in one scanning period, the gear shift multiple can be increased accordingly.

Furthermore, since image data can be obtained from a plurality of tracks by sequentially moving the magnetic head during one scanning period during variable speed reproduction, when reproducing digitally recorded image data, the image is reproduced. Data loss can be reduced.

[0019]

1 is a diagram showing an embodiment of a variable speed reproducing method according to the present invention. Referring to FIG. 1, 4a shows a center running locus when the magnetic head 3 is immovable in the track width direction, and 4b shows a center running locus when the magnetic head 3 is variable in the track width direction. Shows the trajectory. The magnetic tape 1 includes an A track recorded with + azimuth and a B track recorded with −azimuth. The magnetic head 3 includes an A head for reproducing the A track and a B head for reproducing the B track. The magnetic head 3 is scanned as follows according to the traveling locus 4b.

First, scanning is started by the A head, and A
Play the beginning of one track. When the magnetic head 3 is not movable in the track width direction, the scanning locus of the magnetic head gradually moves toward the adjacent B1 track as shown in FIG. 9, so that the reproduction output also gradually decreases. , At this time, the head actuator is driven and the A head is
By displacing the track so that it does not come off the track and performing dynamic tracking, reproduction can be performed without reducing the output.

Next, when a preset time (T5 in FIG. 2) has elapsed from the scanning start time, the A head is moved to the A2 track and the A2 track is reproduced. The shorter the movement time at this time, the more time can be added to the reproduction of the track. That is, more image information can be obtained. The moving time of this track is set based on the response of the head actuator and the maximum displacement amount. After the A head completes the movement, the A2 track is reproduced, and one scan by the A head is completed at the end of the A2 track. Here, the scanning head is switched to the B head and scanning is performed in the same manner as the A head.

When the magnetic head is moved from one track to another track, it may be performed when the displacement amount of the actuator reaches a certain value or when the voltage for driving the actuator reaches a certain value. .

FIG. 2 is a diagram showing the reproduction envelope and the amount of displacement of the magnetic head during the scanning period when the magnetic head is scanned as described above.

The reproduction envelope shown in FIG. 2A has a noise period (T7) rather than noise (T4 in FIG. 10) when the magnetic head 3 is fixed in the track width direction.
Becomes shorter. Also, the period (T6) during which the reproduction output is reduced is very short. As a result, the image information obtained in one scanning period can be increased as compared with the case of scanning a plurality of tracks in an oblique direction as shown in FIG.

Further, from FIG. 2B, the stroke S2 of the magnetic head is approximately 2 × track pitch.
It can be seen that the stroke is half that of the stroke S1 shown in FIG.

As a result, in the double speed reproduction method of the present invention,
Even if the number of double speeds is increased, the head stroke does not change to about 2 × track pitch, and it can be applied to higher double speed numbers.

FIG. 3 is a block diagram showing a variable speed reproducing apparatus for carrying out the variable speed reproducing method of the present invention. FIG. 4 is an output waveform diagram of each circuit shown in FIG.

Referring to FIG. 3, this variable speed reproducing apparatus has a pattern voltage generating circuit 6, a subtractor 13, a driving circuit 7, a head actuator 8, a magnetic head 3, a reproducing circuit 9, an error detecting circuit 10 and a switching circuit 11. , And a timing generation circuit 12.

The pattern voltage generating circuit 6 generates the pattern voltage Vp shown in FIG. 4A in response to the shift multiple setting signal IN. The pattern voltage Vp is a signal for scanning the magnetic head 3 according to the scanning locus 4b shown in FIG. 1, and is proportional to the displacement amount of the actuator shown in FIG. The pattern voltage Vp is divided into a period T5 in which the magnetic head 3 follows the track and a period T6 in which the magnetic head 3 is instantaneously moved to a track of the same azimuth, which is one track pitch away from the track currently being followed. In the period T5, the voltage changes gradually because the track is tracked according to the shift multiple, whereas the pattern voltage Vp in the period T6 instantaneously jumps between the tracks, and the voltage changes rapidly. ing.

The subtractor 13 receives the error signal V for correcting the deviation of the scanning track of the magnetic head 3 from the pattern voltage Vp.
The control signal Ve is generated by subtracting e.

The drive circuit 7 displaces the head actuator 8 in response to the control signal Vc.

The head actuator 8 is displaced by the drive circuit 7 and guides the magnetic head 3 to the scanning locus 4b. Since the head actuator 8 needs to move the magnetic head 3 instantaneously by one track pitch, high response is required. A piezoelectric bimorph type is suitable for such an actuator having high response. For example, assuming that the track pitch is 10 μm or less, and the actuator stroke is about ± 10 μm,
Since an actuator with a resonance frequency of about 10 KHz can be realized and a response time of about 0.5 msec can be obtained, the number of pixels that drop out per track jump is about 10% of one field, which is a specification that can be practically used. Become.

The magnetic head 3 includes a head actuator 8
The head actuator 8 takes a scanning locus 4b according to the pattern voltage Vp and reproduces image information from the magnetic tape 1.

The reproducing circuit 9 detects the envelope of the reproduced image signal from the magnetic head 3. Error detection circuit 10
Is a method of comparing the crosstalk level of the pilot signal or comparing the level of the envelope detected one scanning period before with the level of the envelope currently detected, and the magnetic head 3 moves in the track width direction. An error signal Ve for indicating in which direction the deviation is made is output.

The timing generating circuit 12 is shown in FIG.
As shown in, the pulse signal Vt which has a high level in the period T5 of one scanning period and has a low level in the period T6 is generated.

The switching circuit 11 has a pulse signal Vt.
Turn on / off in response to. That is, it is turned on in the period T5, the error signal Ve is transmitted to the subtractor 13, and it is turned on in the period T6 to stop the tracking operation. During this period T6, the pattern voltage generation circuit 6 outputs the pattern voltage Vp to the drive circuit 7 for instantaneously moving it from the currently scanning track to another track.

Next, the operation of the variable speed reproducing device shown in FIG. 3 will be described. First, when the double speed number setting signal IN is input,
The pattern voltage generation circuit generates the pattern voltage Vp so as to follow a preset locus according to the set speed factor. On the other hand, the error signal Ve for the track of the magnetic head 3 is the magnetic head 3 → reproduction circuit 9 → error detection circuit 1
0 → Feed back through the switching circuit 11.

Next, during the period T6 when the magnetic head 3 jumps from one track to another track, the pulse signal Vt is output from the timing generation circuit 12. In response to the pulse signal Vt, the switching circuit 11 is turned off, the closed loop is disconnected, and the variable speed reproducing device is opened. Then, during the open-loop period T5, the pattern voltage Vp whose potential changes rapidly is supplied to the drive circuit 7, and the drive circuit 7 instantaneously displaces the actuator 8 in accordance with the pattern voltage Vp.

By using the variable speed reproducing device as described above, accurate and efficient tracking can be realized during variable speed reproduction.

By the way, when the present invention is applied to a digital VTR, the following problems may occur.

In the digital VTR, image information is recorded in block units, and each image data block forms a part (pixel) of an image appearing on the screen. The arrangement of these image data blocks on the track does not necessarily match the arrangement of the pixels appearing on the screen. The position information of the pixels with respect to the screen is added as an address to each image data block, and each image data block is tracked. In some cases, they are randomly arranged on the top. Further, since the digital VTR has a very large amount of data, it is general to record the image information for one field by dividing it into a plurality of tracks. Such a recording method is called segment recording, but when scanning a segment-recorded track during variable speed reproduction, there may be a case where only a biased pixel in one field can be reproduced depending on the double speed number. Such a state occurs when, for example, the double speed is a multiple of the number of segments / one field.

Therefore, in order to avoid this, it is only necessary to select a multiple speed number other than the multiple speed number which reproduces only a biased segment such as the number of segments / an integral multiple of one field. By doing so, each pixel block is reproduced evenly, and variable speed reproduction with few missing pixels can be realized.

Next, with reference to FIG. 5 to FIG. 7, the manner in which the number of pixels of the reproduced video changes depending on the speed number will be described. FIG. 5 shows the number of pixels of the image reproduced at 4 × speed, and FIG. 6 shows the number of pixels of the image reproduced at 5 × speed,
FIG. 7 is a diagram showing the number of pixels of an image reproduced at 3 × speed.

In FIGS. 5 to 7, for simplification of description, a 4-segment recording format in which 1 frame is formed by 4 tracks is taken as an example, and 5 sync blocks are recorded per 1 segment. It is assumed that the sync block contains one pixel of information. FIG. 5A shows the head locus in the case of the 4 × speed using the present invention, and FIG. 5B shows the pixels on the screen reproduced at that time.

Referring to FIGS. 5 (a) and 5 (b), at the time of quadruple speed, only pixels appearing at the same position on the screen are always reproduced every other scanning, so that only 8 pixels out of 20 pixels are reproduced. Can't play.

Therefore, as shown in FIG. 6 (a), when reproduced at 5 × speed, it is possible to reproduce evenly from each part of the track, and the reproduced image is 12 as shown in FIG. 6 (b). It becomes individual and increases compared to 4x speed. Pixels that drop out at this time are the second and fourth pixels of each track corresponding to the section where the magnetic head 3 makes a track jump during reproduction.

Further, when the 3 × speed reproduction is performed as shown in FIG. 7A, the number of reproduced pixels is further increased to 16 as shown in FIG. 7B, and the omission is small. Become. In this case, the number of track jumps is once per scan, so the number of dropouts is reduced by 4 pixels compared to the 5x speed, which requires two track jumps per scan, and only the third pixel on each track is skipped. Will fall out.

That is, as typified by FIG. 5, when the double speed number is an integral multiple of the number of segments, the number of pixels to be reproduced is very small, and the reproduced screen has many missing pixels and is very difficult to see. . However, by selecting a double speed number other than an integral multiple of the number of segments as shown in FIG. 6 or 7, the pixel dropout is limited to the track jump section, so that the number of pixels to be played back increases and the playback screen is easier to see. Is obtained.

In the description of the variable speed reproduction method of FIGS. 5 to 7, since it is considered that the pixel is considerably coarse, the reproduced screen seems to be insufficient at any speed number, but actually the pixel is not. It is divided into quite small parts, and missing pixels are evenly present in each part on the screen. Therefore, if a certain number of pixels or more are reproduced, it is not so difficult to see.

[0050]

According to the present invention described above, the operation of causing the magnetic head to follow a predetermined track during variable speed reproduction and the operation of moving from the track currently following to at least the closest track of the same azimuth are alternately performed. , It is possible to suppress the period in which the noise bar appears. Further, since the stroke of the actuator can be reduced, the gear shift multiple can be increased. Furthermore, the image information reproduced in one scanning period can be increased, and the loss of pixel data can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a variable speed reproduction method according to the present invention.

FIG. 2 is a diagram showing a displacement of a reproduction envelope and a magnetic head during one scanning period.

FIG. 3 is a block diagram showing a variable speed reproducing device for carrying out the variable speed reproducing method of the present invention.

4 is an output waveform diagram of each circuit shown in FIG.

FIG. 5 is a diagram showing the number of pixels of an image reproduced at 4 × speed according to the present invention.

FIG. 6 is a diagram showing the number of pixels of an image reproduced at 5 × speed according to the present invention.

FIG. 7 is a diagram showing the number of pixels of an image reproduced at 3 × speed according to the present invention.

FIG. 8 is a diagram showing a background of the present invention and is a diagram showing a configuration of a magnetic head and its periphery for realizing a function of a dynamic track.

FIG. 9 is a diagram showing a scanning locus of the magnetic head during variable speed reproduction when the magnetic head is fixed in the track width direction.

10 is a diagram showing a reproduction envelope based on the scanning locus shown in FIG.

FIG. 11 is a diagram showing a scanning locus of a magnetic head according to a conventional variable speed reproducing method using a head actuator.

12 is a diagram showing the displacement of the actuator when the scanning locus shown in FIG. 11 is taken.

[Explanation of symbols]

1 magnetic tape 2 tracks 3 magnetic head 4a magnetic head center locus when the magnetic head is immovable in the tape width direction 4b magnetic head center locus when the magnetic head is variable in the tape width direction 6 pattern voltage generating circuit 7 Drive circuit 8 Head actuator 9 Reproduction circuit 10 Error detection circuit 11 Switching circuit 12 Timing generation circuit 13 Subtractor

Claims (1)

[Claims] 1. A magnetic recording / reproducing apparatus having an actuator for displacing a magnetic head in a track width direction to obtain a maximum reproduction output signal by causing the magnetic head to follow a track, and a speed change set externally. In response to a multiple setting signal, a first control signal for causing the magnetic head to follow a predetermined track among a plurality of tracks included in one scanning period during one scanning period during variable speed reproduction, and the magnetic head. Alternately generate a second control signal for momentarily moving the track from the predetermined track being tracked to the closest track of the same azimuth, and responding to the generated first and second control signals. hand,
A variable speed reproducing method characterized in that the displacement amount of the actuator is controlled to sequentially move the magnetic head to a plurality of tracks included in the one scanning period so as to follow the destination track.