JPS60214443A - Skew distortion correcting device - Google Patents

Abstract

PURPOSE:To eliminate skew distortion by adding the output of the 1st sample- and-hold and the output of the 2nd sample-and-hold to form an error signal and controlling the tension of a magnetic tape in response to the error signal. CONSTITUTION:The behavior of the processing, as to the output of the 2nd phase comparator circuits 13, 31 and an output of the 1st and 2nd sample-and- hold circuits 14, 32, is an output of broken lines in Figs. A, B, C, D. Error outputs are added by an adder circuit 33, the relation of (E+e)+(E-e)=2E is obtained, where E is an error output by skew distortion and (e) is a false error output, the false error output is cancelled and only the true error due to skew distortion re ains. The error signal is fed to a filter 15, its output is led to an amplifier 16 to control the torque of a reel motor 17. The tension of the magnetic tape is controlled by the torque control, and feedback control zeroing the phase error is attained thereby keeping the elongation of the magnetic tape the same as that at recording. Then the skew distortion is corrected.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to skew distortion correction I! The present invention relates to a device, and particularly to a skew distortion correction device in a pilot signal type magnetic recording/reproducing device.

[Prior art vFI] In a two-head magnetic recording/reproducing device, a magnetic tape is wound diagonally approximately 180 degrees around a head drum having two rotating magnetic heads, and each head sequentially scans the magnetic tape in the diagonal direction. At the same time, the magnetic tape is run at a constant speed to sequentially form video signal tracks on the magnetic tape.

Recently, the magnetic tape has been attached to the head drum more than 180 degrees.
For example, by wrapping 220 degrees to make each recording track longer,
A video signal is recorded for 180 degrees on each recording track, and the remaining portion is recorded with, for example, time-compressed PCM audio, and furthermore, a pilot signal for tracking is superimposed on these signals and recorded. A magnetic recording/reproducing device configured as follows is used. In this case, when one rotating magnetic head is recording a video signal, the other rotating magnetic head is simultaneously recording 1) a CM signal at the end of an adjacent track during a part of the period; During the period, the pilot signal superimposed on the video signal is simultaneously PCM
It is also superimposed on the signal and recorded.

FIG. 1 shows how a magnetic tape is wound around a head drum in a conventional magnetic recording/reproducing device.
(not shown).

The head drum 2 includes two rotating magnetic heads 3a.

3b is separated by an angular interval of 180 degrees and the head drum 2
It is provided so as to be exposed on the peripheral surface of.

One rotating magnetic head is 220°-18° from the tape entrance.
During the scanning period of the 0°-400° portion, the two rotating magnetic heads 3a and 3b are in contact with the magnetic tape 1 at the same time. When the magnetic tape 1 runs at a constant speed in the direction of the arrow in the figure, when one of the rotating magnetic heads forms a recording track, the other rotating magnetic head simultaneously moves to the above-mentioned position during a period corresponding to the 40° portion. It is forming a track adjacent to the track. A track pattern formed on the magnetic tape 1 in this manner is shown in FIG. A PCM signal is recorded in the A section of the tracks T, , T, . . . , and a video signal is recorded in the B section. In addition, if the pilot signal for tracking uses a so-called 4-frequency pilot signal system, the frequency f + ,
Pilot signals of rz, fa + f4 are recorded superimposed on the video signal. These pilot signals are used for tracking during reproduction, and the crosstalk of these pilot signals is reproduced from both adjacent tracks of the track being obliquely scanned by the rotating magnetic head to form a tracking error signal. For example, if the rotating magnetic head 3a is on the track T
When scanning part B of It can be used as an error signal for tracking servo feedback. In order to facilitate the W4 difference signal detection system, there are +f + -f between the above frequencies.
21-1f, -zu 4 1-F+, If' 2 f
The relationship is s 1-1f + -f+I-Fz. For example, f, -103kHz, f2-119
kHz, re=165 kHz, f*=149
k)lz, then F+ -16k)lz,
There is F2-46 kHz 'T'.

When reproducing a magnetic tape on which tracks have been formed as described above, tracking servo is applied by utilizing the crosstalk of the pilot signal, and the video signal and PCM signal are reproduced by the two rotating magnetic heads. FIG. 4 shows the envelope of the signal reproduced by the soft magnetic head both times, and the video signal and the PCM signal are simultaneously reproduced at the 40° portion of the head drum. These signals also include the pilot signal of the scanning track and the pilot signals of the adjacent tracks on both sides.

The tracking servo operates as follows.

First, in synchronization with the number of circulations of the head drum, every half rotation of the head drum corresponding to the above 1806, the frequency f, ,
Oscillation signals of f, j's, and F4 are generated in a predetermined repeating order. On the other hand, the reproduced signal obtained by the rotating magnetic head is produced by a switcher controlled by a switching pulse generated every half rotation of the head drum.
, the continuous playback video signal and the time-compressed playback P
The CM signal and the CM signal are divided and derived. Next, a reproduced pilot signal as described above is extracted from the reproduced video signal using a bandpass filter (BPF). These pilot signals and the above oscillation signal are applied to a frequency converter, and the output is passed through two bandpass filters B having center frequencies F and F2.
When applied to PF (F+) and BPF (F2), the above-mentioned difference frequency components F and F2 are generated at the outputs of both BPFs, and when these two components are compared in level using a differential amplifier, etc. The amount of track deviation of the rotating magnetic head is detected, and this detection signal is fed back to a capstan servo system, etc., so that the track deviation can be corrected. The tracking servo operates in this way. When the tracking servo reaches a steady state, the rotating magnetic head starts scanning over a track on which a pilot signal of a frequency corresponding to the currently generated oscillation signal among the oscillation signals is recorded. For example, if the oscillation signal has a frequency f, then the rotating magnetic head 3a is scanning eight parts of the track T.

Now, let us consider a case where the tracking servo is applied as described above and the reproduced video signal becomes an appropriate demodulated signal and is sent to a television to become a reproduced screen. As mentioned above, since the reproduced video signal is a continuous signal obtained by connecting the outputs of two rotating magnetic heads using a switcher, there is always a seam. If the elongation of the magnetic tape is exactly the same during recording and playback, there will be no deviation in the time base of the signal before and after this seam, and the connection will be smooth. However, if there is a difference in the elongation of the magnetic tape, the difference will occur before and after the seam. The time base is out of order and the phase of the signal changes in a step manner at the seam. For example, when a magnetic tape is stretched, the phase after the seam always advances in a step manner. Conversely, when the magnetic tape shrinks, the phase after the seam always lags in a step manner. For this reason, the reproduced screen has the disadvantage that so-called skew distortion occurs, which is distortion at the seam portion. - As an example, if a vertical bar such as a telephone pole is displayed on a TV equipped with AFC, it will look like the image shown in Figure 3. Skew distortion can be reduced by magnetic tape tension servo, but
Generally, the tension of the magnetic tape is detected and the tension is adjusted to a preset value, and it is not always possible to completely eliminate skew distortion.

[Summary of the Invention] The present invention has been made to improve such drawbacks, and therefore, the main object of the present invention is to eliminate skew distortion in a pilot signal type magnetic recording/reproducing device. An object of the present invention is to provide a skew distortion correction device.

To summarize the invention, in a pilot signal type magnetic recording and reproducing device, a pilot signal is reproduced from an odd-numbered track by a first magnetic head, and at the same time as this reproduction,
the second from the end of the track adjacent to the odd-numbered track
A pilot signal having the same frequency as the above-mentioned reproduced pilot signal is reproduced using a magnetic head, and the two reproduced pilot signals are compared and the output is sampled and held, and then,
A second magnetic head reproduces a pilot signal from an even-numbered track, and at the same time, a pilot signal having the same frequency as the reproduced pilot signal is reproduced from an end of a track adjacent to the even-numbered track by a first magnetic head. , compare the reproduced pilot signals of both, sample and hold the output, then add the sample and hold outputs of both to obtain an error signal, and control the tension of the magnetic tape according to this error signal. This is a skew distortion correction device.

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

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

FIG. 5 is a block diagram at the time of skew distortion correction@stomach regeneration according to an embodiment of the present invention. In the figure, the rotating magnetic heads 3a and 3b are connected to head amplifiers 118 and 111, respectively.
connected to the switcher 20 via b,
20 is connected to a video signal processing circuit 27 and a PCVM signal processing circuit 28. Additionally, the timing signal generation circuit 19
is connected to switcher 20. Rotating magnetic head 38
3b is amplified by the head amplifier 118.11b and then applied to the switcher 20. Switcher 2
0, the video signal and the PCM signal are each extracted at appropriate timings by the output of the timing signal generation circuit 19. The video signal is made into a continuous reproduction signal and guided to the video signal processing circuit 27, where it is converted into a television signal!
be involved. In addition, the PCM signal is processed by the PCM signal processing circuit 28.
The signal is guided to the audio signal, undergoes processing such as time expansion, and is demodulated into a continuous audio signal. A rotation detector 18 is provided on the side of the head drum 2, and the rotation detector 18 is connected to a frequency converter 23 via a timing signal generation circuit 191 and an oscillator 21.
connected to. Further, the switcher 20 is connected to a frequency converter 1123 via a BPF 22. The frequency converter 23 is a tracking processing circuit 24. It is connected to a capstan motor 26 via an amplifier 25. The oscillator 21 has frequencies f , , f2 . The signals f, , f are sequentially generated, and the switching of the oscillation frequency is performed by the timing signal generating circuit 19, which operates based on the rotation detector 18 that detects the rotational phase of the head drum 2, as described above. This is done every half rotation of the drum 2.

In addition, the BPF 22 extracts a reproduced pilot signal from the video signal and PCM signal extracted by the switcher 20,
The pilot signal component extracted here and the oscillation signal of the oscillation 121 are applied to the frequency converter 23, and the difference frequency signal component between the oscillation signal frequency and the pilot signal frequency is given to the tracking processing circuit 24 and is processed as described above. Track deviation detection is performed. An error signal corresponding to the amount of track deviation is applied to the amplifier 25, and the capstan motor 2
6 is performed to control the feeding of the magnetic tape 1, so that the rotating magnetic heads 3a and 3b scan the tracks correctly. Head amp"jI8.11b
are respectively BPF12a and '! 2b to a first phase comparison circuit 13, and this phase comparison circuit is connected to a first sample and hold circuit 14. In addition, the timing signal generation time wi19 is the sample hold time 11 of 11.
Connected to 4. Furthermore, head amplifier 118.11b
is connected to a second phase comparison circuit 31 via BPFs 30a and 30b, and this phase comparison circuit is connected to a second sample and hold circuit 32. Further, the timing signal generation circuit 19 is connected to a second sample and hold circuit 32. First and second sample and hold circuits 14.3
2 are connected to an adder circuit 33, which is connected to the filter 15.2. It is connected to a reel motor 17 via an amplifier 16.

The outputs of the head amplifiers 11a and 11b are further subjected to the following processing in order to achieve the skew distortion correction that is the object of the present invention. These outputs are each BPFI 2
a, 12b. These BPFI 2a,
It is assumed that the center w4 wave number of 12b has a specific frequency among the pilot signal frequencies, for example, fl. Therefore, the pilot signal of frequency f is extracted from the reproduced signal by the BPFI 2a, 12b. Assuming that the magnetic tape 1 is under running control and reproducing normal signals by the tracking servo, the output signals of the BPFIs 2a and 12b are the sixth
The result will be as shown in Figures (A) and (B). However, since we are focusing only on the above-mentioned 40'' portion, only the reproduced pilot signal from the track scanned by the rotating magnetic heads 3a and 3b is drawn in consideration.In other words, the pilot signal due to crosstalk is Although the signal t occurs in other sections, it is ignored.

Next, the outputs of these BPFIs 2a and 12b are applied to the first phase comparison circuit 13, and a phase error between the two is generated, for example, as shown in FIG. 1ilIa (C).

Here, if the elongation of the magnetic tape 1 does not change at all from the time of recording, the pilot signal is simultaneously recorded in the 40° section by the rotary magnetic heads 3a and 3b, so it will not change at the time of playback. re-rotating magnetic head 3a,
The pilot signals reproduced from 3b are signals with the same timing. Therefore, the output of the first phase comparison circuit 13 becomes 0. However, if the magnetic tape 1 is to be played back in a state where the tension is stronger and slightly stretched than when it was recorded, the position of the playback pilot signal of the rotating magnetic head 3a and the playback pilot signal of the rotating magnetic head 3b will be changed. A phase difference occurs. This situation is shown in the enlarged view of FIG.

That is, when the magnetic tape 1 is stretched, as shown in FIG. 7(B)
As shown by the broken line, BP
Fl 2b 17) Output leads in phase. In addition, if the magnetic tape has shrunk since recording, as shown by the dashed line in FIG.
The output of PF12b is delayed in phase. In this way, if the elongation state of the magnetic tape 1 is different from that during recording, a phase difference occurs between both pilot signals, and an error voltage is generated in the first phase comparator circuit 13 in accordance with the elongation and contraction of the magnetic tape 1. . This a
This occurs only in the 40° portion of the R difference voltage, and moreover, it occurs once every four times when the rotating magnetic heads 3a and 3b sequentially scan the track.

In other words, this occurs once every two rotations of the head drum 2. Since the Ill differential voltage is not generated continuously in this way, the timing generating circuit 19 generates sampling pulses at the timing shown in FIG. 6<D> once every two revolutions of the head drum 2. When this error voltage is sampled and held by generating it and applying it to the first sample-and-hold circuit 14 in FIG. 5, an output as shown in FIG. 6(E) is obtained, for example.

In the above explanation, the error voltage generation process was described when only the elongation of the magnetic tape 1 changes in the case of self-recording/playback, but the following two cases need to be considered. In the first case, when this magnetic recording and reproducing practice follows the so-called inclined azimuth recording method, since adjacent tracks are recorded with opposite azimuths, the rotating magnetic heads 3a and 3b are tracked during reproduction. Even if the servo is scanning a regular track, if it does not scan the same trajectory as during recording, that is, if the trajectory of the rotating magnetic heads 3a, 3b becomes a trajectory that deviates slightly from that during recording, the time base will change at the joint. As a result, a phase difference occurs every half rotation of the rotating magnetic heads 3a and 3b. However, the manner in which this phase difference occurs is the same as in the case of the above-mentioned skew distortion, and the phase advances, goes back, advances, lags, etc. before and after the joint every half rotation of the rotating magnetic heads 3a and 3b.

Consider a case where this time base deviation is added to the above skew distortion. Considering the generation of error voltage due to skew distortion, as described above, the rotating magnetic heads 3a, 3b
An error voltage is generated every time the rotating magnetic heads 3a and 3b sequentially scan the track four times, that is, every time the rotating magnetic heads 3a and 3b make 4 half rotations. , 3b sequentially scan the track four times, as can be seen from the above, it is always in one direction, that is, in one direction, leading or trailing. This advance or lag is determined by the rotating magnetic head 3a.

Is the trajectory of 3b shifted to the right with respect to the track?
It depends on whether it is shifted to the left. Therefore, in this case, the output of the first phase comparison circuit 13 contains a false error due to head trajectory deviation in addition to the error due to skew distortion, for example, as shown by the broken lines in FIGS. This will result in a false output.

Next, in the second case, when performing compatible reproduction, if the mounting angles of the two rotating magnetic heads 3a and 3b match that of the magnetic recording and reproducing device that recorded, then the phase will also be stepped at the joint. changes. The manner in which the phase difference occurs in this case is exactly the same as in the first case, in which the phase difference advances and lags every half rotation of the rotating magnetic heads 3a and 3b before and after the seam.

Repeat... Therefore, the first phase comparison circuit 13
A false w4 difference signal similar to the first case is generated at the output of .

Therefore, in order to eliminate these false WA difference signals, we will return to FIG. 5 and explain. BPF3Qa in Figure 5, 30
b has a center frequency at a frequency f2 next to the frequency f. Therefore, during the half-rotation period of the rotary magnetic heads 3a, 3b that follows the generation of the above-mentioned error signal, the pilot signal of f2 is regenerated, so that the BPFs 30a, 30
b, the output of the second phase comparison circuit 31 is as shown in FIG. 6(A).
,(B).

A waveform similar to the waveform shown by the solid line in (C) is obtained.

Further, the timing generation circuit 19 generates a sample pulse delayed by about 1806 times from the sample pulse shown in FIG.
2 and sample and hold the output of the second phase comparison circuit 31, a waveform similar to the waveform shown by the solid line in FIG. 6(E) is obtained. Next, if there is the above-mentioned track trajectory deviation or angular deviation of the rotating magnetic head, the phase advance and lag are reversed before and after the seam every half rotation of the rotating magnetic heads 3a and 3b as described above. Second phase comparison circuit 31 and second sample hold circuit 3
The false error signal appearing at the output of 2 is equal in absolute value to that described above, but appears in the opposite direction to the direction shown by the dashed lines in FIGS. 6(C) and (E).

The above situation is explained in the first and second phase comparator circuits 13.31
output and the first and second sample and hold circuits 1
Figure 8 shows the output of 4.32 (A>, (B),
(C) and (D) are the broken line outputs. Figure 8 (C), (D
), the error output due to skew distortion is shown as E, and the above false w4 difference output is shown as e. Next, if these error outputs are added in the adder circuit 33, (E+8 >+ (
E-1)-2E, and the above false error output is canceled out,
Only the true error due to skew distortion remains. Note that since the skew distortion error output is obtained as twice the original value, it also has the advantage of increased sensitivity. Applying this error signal to the filter 15,
The output is guided to an amplifier 16 to control the torque of the reel motor 17. This torque control controls the tension of the magnetic tape, and performs feedback control such that the phase error becomes O. In this way, the elongation of the magnetic tape can be maintained at the same level as during recording, and skew distortion can be corrected.

In the above embodiment, a case has been described in which skew distortion is corrected by combining pilot signals f and f2, but which combinations of pilot signals (f+ and f4), (f2 and "."), (fs and t,) You may also use

□ Also, in the above embodiment, P is placed at the front end of each track.
Although a case has been described in which CM audio is recorded and a video signal is recorded after that, the present invention can be similarly applied even if the order of these signals is reversed.

Moreover, although the pilot signal has been described as having four frequencies, it is not necessarily limited to four.

[Effects of the Invention] As described above, according to the present invention, in a pilot signal type magnetic recording/reproduction iut, the pilot signal reproduced by the first rotary magnetic head from the odd-numbered track,
Simultaneously with this reproduction, the phase of the above-mentioned reproduced pilot signal and a pilot signal of the same frequency, which is reproduced from the end of the track adjacent to the odd-numbered track by a second rotating magnetic head, is compared, and this comparison output is sampled. hold to obtain a first sample-and-hold output, and then, at the same time as the pilot signal reproduced by the second rotating magnetic head from the even-numbered track, and the end of the track adjacent to the even-numbered track. The phase of the reproduced pilot signal and a pilot signal of the same frequency, which are reproduced by the first rotating magnetic head, are compared, the comparison output is sampled and held, and the second sampled and held output is stored. The first sample hold output and the second sample hold output are added to form an error signal, and the tension of the magnetic tape is controlled according to this error signal, so that the elongation of the magnetic tape during playback is equal to the elongation during recording. can be kept the same, and skew distortion can therefore be removed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing how the head drum and magnetic tape are wound. FIG. 2 is a diagram showing a track pattern on a magnetic tape. FIG. 3 is a diagram showing an example of skew distortion in a reproduced image. FIG. 4 is a diagram showing a reproduction output envelope of the rotating magnetic head. FIG. 5 is a diagram showing an embodiment of the present invention. FIG. 6 is a waveform diagram for explaining one embodiment of the present invention. FIG. 7 is a waveform diagram for explaining the phase relationship of reproduced pilot signals. FIG. 8 is a diagram showing the relationship between an error signal due to skew distortion and a false error signal. In the figure, 1 is a magnetic tape, 2 is a head drum, and 3a
, 3b is a rotating magnetic head, 118.11b is a head amplifier, 12a, 12b, 30a, 3Qb are 8PFs, 13 is a first phase comparison circuit, 31 is a second phase comparison circuit, 14
is the first sample and hold circuit, 32 is the 1112 sample and hold circuit, 15 is the filter, 16 is the amplifier, 1
7 is a reel motor, 18 is a rotation detector, 19 is a timing signal generation circuit, and 33 is an addition circuit. Agent Masuo Oiwa Figure 1 Figure 2 + 4 1wo 12 1+ Figure 3 Figure 4 Figure 6 Figure 7

Claims (1)

[Claims] First and second rotating magnetic heads are installed on the rotating head drum at an angular interval of 180 degrees from each other, and these rotate the magnetic tape diagonally to sequentially scan parallel inclined tracks. and during recording, an information signal is recorded along with a pilot signal of a frequency that changes in a predetermined repetition order for each track, and further, the length of the track is set to the angular interval between the first and second rotating magnetic heads. The length of the first track is set longer than the corresponding length, and the length of the first track is set longer than the corresponding length.
and a second rotating magnetic head are brought into contact with the magnetic tape at the same time, and the pilot signal is recorded in the predetermined repetition order on the end portion at the same time as the pilot signal of the 1-rack is recorded. , and the frequency of the pilot signal recorded on one of the ends is the same as the frequency of the pilot signal recorded on the track one track ahead or behind one of the ends, and reproducing. Sometimes, in a pilot signal type magnetic recording and reproducing apparatus configured to sequentially reproduce the pilot signal having a frequency that changes in the repetition order from each of the tracks by each of the first and second rotating magnetic heads, The pilot number M is reproduced from the odd-numbered track by the first rotary magnetic head, and simultaneously with this reproduction, the pilot number M is reproduced from the end of the track adjacent to the odd-numbered track by the second rotary magnetic head. a first phase comparison means for comparing the phase of the reproduced pilot signal having the same frequency as the pilot signal reproduced by the first rotary magnetic head; a first sample and hold means L that samples and holds the output of the means and outputs a first sample and hold output; a first sample and hold means L that samples and holds the output of the means; At the same time, the pilot signal is reproduced from the end of the track adjacent to the even-numbered track by the first rotary magnetic head, and has the same frequency as the pilot signal reproduced by the second rotary magnetic head. a second phase comparison means that compares the phase of the frequency with the pilot signal; and a second sample and hold means that samples and holds the output of the second phase comparison means and outputs a second sample and hold output. , an addition means for adding the first sample hold output and the second sample hold output to generate an error signal, and a tension control means for controlling the tension of the magnetic tape according to the error signal. A skew distortion correction device characterized by: