GB1582486A - Methods of recording video signals - Google Patents

Description

(54) METHODS OF RECORDING VIDEO SIGNALS (71) We, SONY CORPORATION, a corporation organised and existing under the laws of Japan, of 7-35 Kitashinagawa-6, Shinagawa-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to. methods of recording video signals.

In a rotary head drum assembly of a two head helical type video tape recorder (VTR), as shown in Figure 1A and Figure 1B, two magnetic heads la and ib are arranged diametrically to each other in a rotatable upper drum 2a of a tape guide drum 2. The tape guide drum 2 comprises the rotatable upper drum 2a and a stationary lower drum 2b. A magnetic tape 3 is slantly wrapped around the tape guide drum 2 over an arc of about 1800, and is transported in the direction shown by the arrows in Figure 1A and Figure 1B. The magnetic heads la and ib are rotated in the direction shown by the arrow in Figure lA at the rate of 30 revolutions per second by an electric motor M. Further. a magnet 4 rotating with the magnetic heads la and Ib and a stationary pick-up head 5 are arranged in the tape guide drum 2. A position detecting pulse is generated from the pick-up head 5, in response to the rotational positions of the magnetic heads la and ib. If necessary. two pick-up heads 5 may be provided.

When video signals are recorded on the magnetic tape 3. parallel slant tracks Ta1, Tub1, Ta,--- are formed on the magnetic tape 3 alternatelv bv the magnetic heads la and ib, as shown in Figure 2A. One field of video signals is recorded on the respective track Ta,. Tbl, Ta ---by the magnetic head la or Ib.

When the magnetic tape 3 is run to reproduce the signals. a tracking servo system is employed in order to make the magnetic heads la and ib trace, or scan, the recorded tracks Ta1, Tub1, Ta2 --- correctly.

In the tracking servo system, the relative speed between the magnetic heads la and ib, and the magnetic tape 3 is controlled with control signals recorded on the margin of the magnetic tape 3 and the detecting signals of the pick-up head 5, so as to be equal to the relative speed between the magnetic heads la and lb, and the magnetic tape 3 in the recording mode. However, even with the tracking servo system, the play-back scanning traces of the magnetic heads la and ib often do not coincide perfectly with the recorded tracks Ta1, Tub1, Ta2 ---. The reason for this may be, for example, that when the signals are recorded and reproduced in different VTRs, the rotational orbits of the magnetic heads la and ib in the different VTRs are not the same. Or the reason may be that there is an error which cannot be eliminated by the tracking servo system.

When the width of the recorded track is reduced in order to increase the recording density of the magnetic tape 3, or when the magnetic tape 3 is run slower for a long time recording and reproducing operations than for the normal recording and reproducing operations. in the same VTR, tracking error has a serious affect on reproducing characteristics such as signal-to-noise ratio.

For example, Figure 2A shows a pattern of recorded tracks in the case when the signals are recorded on the magnetic tape at the normal tape running speed. In this case, the track pitch is 60C1, the widths of the recorded track and of the guard band being 30fit.

When the tape running speed of the magnetic tape is one third as high as the normal tape running speed. in the recording operation, a pattern of recorded tracks is formed on the magnetic tape, as shown in Figure 2B. Since the tape running speed of the magnetic tape 3 is generally very low in comprison with the relative speed between the magnetic heads la and tb, and the magnetic tape 3, the inclination of the recorded track in the one third tape running speed, as shown in Figure 2B, is nearly equal to the inclination of the recorded track in the normal tape running speed, as shown in Figure 2A. However, in the case of Figure 2B, the track pitch is one third as wide as that in the case of Figure 2A, namely 20fit. No guard band is formed in the pattern of Figure 2B. In this case, it is required that the magnetic head la or 1b scans exactly one recorded track and 10Ci width portions of the adjacent recorded tracks. When the magnetic head la or ib does not exactly scan the recorded track, beat interferrence occurs due to cross-talk from the adjacent recorded track to deteriorate the reproduced picture.

According to the present invention there is provided a method of recording trackingerror correcting signals added to a video signal on a record medium, said trackingerror correcting signals being for use in detecting errors in the scanning path of a scanning transducer which scans parallel record tracks across said medium, the method comprising: scanning successive record tracks across said medium to record periodic video signals in said record tracks, said video signals containing periodic horizontal synchronizing signals; generating pilot signals during predetermined portions of the horizontal synchronizing signals in said video signals; and recording said pilot signals in said successive tracks such that the position of a pilot signal in one track is shifted with respect to the position of a pilot signal in an adjacent track.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure IA is a schematic plan view of a rotary two head helical type VTR; Figure IB is an elevational view of the VTR of Figure IA, partly broken away; Figure 2A and Figure 2B are examples of recorded tracks formed on a magnetic tape; Figure 3A is an elevational view of a bi-morph leaf; FigurE 3B and Figure 3C are views for explanation of the operation of the bimorph leaf of Figure 3A: Figure 4A is an elevational view of a hi-morph leaf assembly supporting a magnetic head; Figure 4B is a bottom view of the bimorph leaf assembly of Figure 4A: Figure 5 is a block diagram of a recording arrangement; Figure 6A to Figure 6D are waveforms for explanation of the operation of the recording arrangement of Figure 5; Figure 7 shows the relationship between one magnetic head and adjacent recorded tracks, for three ways of scanning; Figure 8 is a block diagram of a reproducing arrangement; Figure 9A to Figure 9E are waveforms for explanation of the operation of the reproducing arrangement of Figure 8; and Figure 10 is a graph showing the relationship between the outputs of peak level detectors in Figure 8 and the tracking deviation or error of the magnetic head.

The magnetic heads la and lb are supported on bi-morph leafs which include piezo-electric sections, and drive signals are supplied to the bi-morph leafs to bend, or deflect, the latter so as to compensate for tracking errors.

Figure 3A shows one example of a bimorph leaf. The bi-morph leaf includes a pair of plate-like piezo-ceramic members 7 and 9. Electrodes 6a and 6b, and 8a and 8b are plated on both sides of the piezoceramic members 7 and 9, respectively. The electrodes 6b and 8a contact each other.

The directions of the polarizations of the piezo-ceramic members 7 and 9 are the same as each other, as shown by the arrows in Figure 3A.

When an electric field is applied to the above-described bi-morph leaf in the manner shown in Figure 3B, the piezo-ceramic member 7 is elongated, while the piezoceramic member 9 is shortened, in the lengthwise directions as shown by the arrows in Figure 3B. As a result, the bi-morph leaf bends as shown in Figure 3B.

The bending displacement depends on the strength of the applied electric field. When the reverse electric field is applied to the bi-morph leaf, the latter bends in the reverse direction.

Figure 3C shows the case where the electrode 6a contacts the electrode 8a so that the direction of the polarization of the piezo-ceramic member 7 is opposite to the direction of the polarization of the piezoceramic member 9. No voltage is applied to the mated electrodes 6a and 8a, while a bias voltage vy2 is applied to the electrode 8b, and a variable (0 to Vo) drive voltage V is applied to the electrode 6b. When the drive voltage V is lower than the bias voltage vet/2, the bi-morph leaf bends downwardly, as shown in Figure 3C. When the drive voltage V is higher than the bias voltage vO/2, the bi-morph leaf bends upwardly.

Figure 4A and Figure 4B show a bi-morph leaf assembly supporting a magnetic head.

As shown in Figure 4A and Figure 4B, a mounting base lü is fixed to the lower surface of the upper head drum 2a. The base end of the bi-morph leaf is fixed to the mounting base 10 by adhesive 11. The leaf is so arranged that the surfaces of the piezoceramic members 7 and 9 are parallel with the lower surface of the upper head drum 2a. The magnetic head la or 1b is attached to the free end of the leaf. The lengthwise direction of the air gap of the head la or 1b is perpendicular to the surfaces of the members 7 and 9. And the surfaces of the members 7 and 9 are substantially perpendicular to the rotational shaft of the upper head drum 2a.

Damper members 13a and 13b such as rubber are provided for damping free oscillation due to the bending force applied to the piezo-ceramic leaf. The damper members 13a and 13b are attached to a pair of tabs 12a and 12b fixed to one end of a damper mounting plate 14 which is fixed to the lower surface of the upper head drum 2a. The damper mounting plates 14 extend towards the periphery of the upper head drum 2a from the outward side of the mounting base 10. The damper members 13a and 13b are pressed between the sides of the bi-morph leaf and the tabs 12a and 12b, respectively. Lead wires are connected to the electrodes of the bi-morph leaf. When a certain voltage is applied to the lead wires in the manner as shown in Figure 3C, the bi-morph bends downwardly or upwardly to move the magnetic head la or 1b in the direction substantially perpendicular to the rotational orbit of the magnetic head la or lb, as shown by the arrow in Figure 4A.

Neither the drive voltage nor the bias voltage is applied to the lead wires of the bi-morph leaf in the recording mode of the VTR. Video signals are recorded on the magnetic tape 3 to form the tracks. When the signals are reproduced from the magnetic tape 3, the bias voltage and a drive voltage as hereinafter described are supplied to the bi-morph leaf to bend the latter so as to compensate for tracking errors.

Next, a recording arrangement will be described with reference to Figure 5 to Figure 9.

In Figure 5, a composite colour video signal is applied to an input terminal 15. It is supplied through the input terminal 15 to a low-pass filter 16 and a band-pass filter 17.

A luminance signal separated at the lowpass filter 16 is supplied to a FM modulator 18. The frequency-modulated luminance signal from the FM modulator 18 is supplied to a high-pass filter 19 to eliminate undesired signal components. and supplied to an adder 20.

On the other hand, a chrominance signal from the band-pass filter 17 is supplied to a frequency converter 21. The carrierfrequency (3.58 MHz) of the chrominance signal is converted to a lower carrierfrequency, for example, to 688 KHz at the frequency converter 21. The frequencyconverted chrominance signal is then supplied to a low-pass filter 22 to eliminate undesired signal components, and supplied to the adder 20. The chrominance signal converted to the lower frequency (688 KHz) and the frequency-modulated luminance signal are mixed with each other at the adder 20. A usual recording signal is obtained from the adder 20. The abovedescribed construction of the recording system is substantially the same as that of a usual colour VTR.

The output of the adder 20 is supplied to another adder 23 to be mixed thereat with a pilot signal which is supplied through a gate circuit 25 from a pilot signal oscillator 24.

The oscillator 24 generates a sine wave of a frequency that is lower than the frequency band of the frequency-modulated luminance signal, and can be separated from the carrier-frequency of the frequencyconverted chrominance signal. The output of the oscillator 24 is supplied to the gate circuit 25. The video signal from the lowpass filter 16 is supplied to a horizontal synchronizing separator circuit 26. A horizontal synchronizing signal separated at the separator circuit 26 is supplied to a monostable multivibrator 27 to form a gate pulse.

The gate pulse is supplied to the gate circuit 25.

Figure 6A to Figure 6D show the time relationships between the waveforms obtained in the circuit of Figure 5. Figure 6A shows the horizontal synchronizing signal. Figure 6B shows the output of the oscillator 24. Figure 6C shows the gate pulse obtained from the monostable multivibrator 27. The pilot signal is added in the section including no burst signal within the period of the horizontal blanking signal, at the adder 23, as shown in Figure 6D. The output of the adder 23 is supplied through a recording amplifier (not shown) to the rotary magnetic heads la and 1b to be recorded on the magnetic tape 3.

The horizontal synchronizing signals including the pilot signals, in the video signal, are recorded on the magnetic tape 3 in the manner shown in Figure 7. Referring to Figure 7, the positions H,, H2, and H3 on which the horizontal synchronizing signals are recorded, are represented by the solid lines perpendicular to the longitudinal directions of the adjacent recorded tracks Ta, Tb, and Ta2. The positions H,, H2 and H3 are slightly shifted from each other. When the signals are recorded on the magnetic tape 3 so that the distance between the terminal ends of the adjacent tracks is odd times as long as the distance of 0.5 H, where H represents the distance on the magnetic tape 3 corresponding to the time of one horizontal scanning section, the positions H1, H2 and H3 are aligned with each other.

Preferably, the shift between the positions H1, H2 and H3 is so selected that no chrominance signal and no burst signal are recorded on the shift portions of the magnetic tape between the positions HI, H2 and H3. The shift corresponds to the value of several Fsec in the reproduced video signal.

Figure 8 shows a reproducing arrangement for reproducing the signals from the thus recorded magnetic tape 3. Referring to Figure 8, the reproduced signals from the magnetic heads la and 1b are supplied through a reproducing amplifier (not shown) to a high-pass filter 31 and a low-pass filter 32. The frequency-modulated luminance signal obtained from the highpass filter 31 is supplied through a limiter to a FM demodulator 34. The output of the FM demodulator 34 is passed through a low-pass filter 35. The luminance signal is obtained from the low-pass filter 35, and supplied to an adder 36.

On the other hand, the frequencyconverted chrominance signal and the pilot signal are separately obtained from the low-pass filter 32, and supplied to a frequency converter 37. The output of the frequency converter 37 is supplied to a band-pass filter 38. The chrominance signal and pilot signal from the band-pass filter 38 are supplied to the adder 36 to be mixed thereat with the output of the low-pass filter 35.

Thus, the composite colour video signal is obtained from an output terminal 39. The above-described construction of the reproducing arrangement is substantially the same as in the usual VTR.

The output of the band-pass filter 38 is further supplied to gate circuits 40 and 41 to separate the pilot signals as the cross-talk components from the adjacent recorded tracks Ta, and Tea2. The output of the low-pass filter 35 is further supplied to a horizontal synchronizing separator circuit 42. The horizontal synchronizing signal is separated at the horizontal synchronizing separator circuit 42, and supplied to a monostable multivibrator 43. The output of the monostable multivibrator 43 is supplied to another monostable multivibrator 44.

Thus, a gate pulse P, is formed on the basis of the horizontal synchronizing signal. and is supplied to the gate circuit 4O to take out the pilot signal as the cross-talk component from the previous one Ta, of the adjacent recorded tracks. The horizontal synchronizing signal from the horizontal synchronizing separator circuit 42 is further supplied to a monostable multivibrator 45 to form a gate pulse P,. The gate pulse P, is supplied to the gate circuit 41 to take out the pilot signal as the cross-talk component from the next one Ta2 of the adjacent recorded tracks. The outputs of the gate circuits 40 and 41 are supplied to band-pass filters 46 and 47 tuning with the frequency of the frequencyconverted pilot signals, respectively. The outputs of the band-pass filters 46 and 47 are supplied to peak level detectors 48 and 49.

The detecting outputs E, and E2 of the peal level detectors 48 and 49 are supplied to a comparator 50, for example, constructed as a differential amplifier. The output of the comparator 50 is supplied as the drive signal to the bi-morph leaf assemblies supporting the magnetic heads la and lb.

Next, the operation of this embodiment will be described with reference to Figure 7 to Figure 10.

Figure 7 shows three ways in which the recorded track Tb, is scanned by the magnetic head ib. The width of the scanning trace of the magnetic head 1b is larger than the track pitch. The middle magnetic head 1b scans the recorded track Tbl in the first way so that the tracking error is considered to be zero. In the first way, the widths of the portions of the adjacent recorded tracks Tal, and Ta2 on which the magnetic head 1b overlaps are equal to each other. Figure 9A shows the pilot signals from the recorded track Tbl and the pilot signals as the cross-talk components from the adjacent recorded tracks Ta, and Ta2 in the three ways that the recorded track Tb, of the magnetic tape 3 is scanned by the magnetic head lb, which are supplied to the gate circuits 40 and 41. In the first way (the middle magnetic head ib in Figure 7) that the tracking error is considered to be zero, the pilot signal Sa, as the cross-talk component from the adjacent recorded track Ta1, and the pilot signal Sa2 as the cross-talk component front the adjacent recorded track Ta2 are equal in peak level. However, the peak levels of the pilot signals Sal and Sa2 are lower than the peak level of the pilot signal Sb reproduced from the recorded track Tb,, in the first way. In the second way (the left magnetic head ib in Figure 7) that the magnetic head 1b is shifted towards the adjacent recorded track Tal, namely that some tracking error is made, the peak level of the pilot signal Sal as the cross-talk component from the adjacent recorded track Ta, is lower than the peak level of the pilot signal Sb from the recorded track Tb,, but higher than the peak level of the pilot signal Sa2 as the cross-talk component from the adjacent recorded track Ta2, as shown in the middle of Figure 9. And in the third way (the right magnetic head 113 in Figure 7) that the magnetic head Ib is shifted towards the adjacent recorded track Ta2, namely that some tracking error is made, the peak level of the pilot signal Sa, as the cross-talk component from the adjacent recorded track Ta, is lower than the peak levels of the pilot signals Sb and Sa2 from the recorded tracks Tbl and Ta2, as shown in the right hand of Figure 9.

The gate pulses P, and P2 shown in Figure 9B and Figure 9C are supplied to the gate circuits 40 and 41 to pass the cross-talk components Sal and Sa2 shown in Figure 9D and Figure 9E, respectively. The peak levels El and E2 of the cross-talk components Sal and Sa2 are detected by the peak level detectors 48 and 49, and supplied to the comparator 50 to be compared with each other thereat.

When the tracking error is zero, namely when the peak levels E, and E2 are equal to each other, a drive voltage which is such as not to deflect the bi-morph leaf assembly supporting the magnetic head 1b is generated from the comparator 50, and supplied to the bi-morph leaf assembly.

When some tracking error is made as shown by the left magnetic head 1b in Figure 7, the peak level E, of the cross-talk component Sa, is higher than the peak level E2 Of the cross-talk component Sa2, as shown in the middle of Figure 9A to Figure 9E. A drive voltage is then supplied to the bi-morph leaf assembly from the comparator 50 such that the magnetic head 1b supported on the bi-morph leaf assembly is deflected towards the adjacent recorded track Ta2. When some tracking error is made as shown by the right magnetic head 1b in Figure 7, the peak level El of the cross-talk component Sa, is lower than the peak level E2 of the cross-talk component Sa2, as shown in the right hand of Figure 9A to Figure 9E. A drive voltage is then supplied to the bi-morph leaf assembly from the comparator 50 such that the magnetic head 1b supported on the bi-morph leaf assembly is deflected towards the adjacent recorded track Ta,.

In Figure 8, the gate pulses Pl and P2 are formed on the basis of the horizontal synchronizing signal separated at the horizontal synchronizing separator circuit 42. However, the gate pulses P, and P2 may be formed on the basis of output pulses of a horizontal scanning frequency obtained from an AFC circuit (not shown).

As apparent from the above description, the outputs E, and E, of the peak level detectors 48 and 49 are nearly proportional to the tracking error, or deviation, as shown by the solid line in Figure 10. When the output E, is equal to the output E2, the tracking deviation is zero. The direction and magnitude of the tracking deviation can be detected by the difference between the outputs El and E2. IF the track pitch is equal to the width of the scanning trace of the magnetic head ib, the outputs El and E, vary with the tracking deviation in the manner as shown by the dotted line in Figure 10. When the tracking deviation is zero, the outputs El and E2 are zero.

While there has been described the operation of the magnetic head ib, the above description for the magnetic head ib also applies to the magnetic head la.

As described, since the tracking deviation is detected at every period of the horizontal scanning sections, the magnetic heads la and ib can scan the recorded tracks with high accuracy. Particularly, when the signals are recorded and reproduced at a lower tape running speed than the tape running speed for the normal recording and reproducing operations, the described method is particularly advantageous. Moreover, since the pilot signal is included in the predetermined position of the horizontal blanking signal, no beat interference due to the pilot signal forming a cross-talk component occurs on the reproduced picture. The pilot signal can be included in the predetermined position of the horizontal blanking signal, with reference to the horizontal synchronizing signal, and can be separated from the horizontal blanking signal, with reference to the horizontal synchronizing signal.

In the above description, the pilot signal is included in the predetermined section containing no burst signal. However, the burst signal, which is not shown in Figure 6A and Figure 6D, may be used as the pilot signal. In that case, the above-described pilot signal (Figure 6B) does not need to be added in the horizontal blanking signal.

Although the bi-morph leaf including the piezo-electric sections described as being used to move the magnetic head, any other transducing means may be used to move the magnetic head. The invention may also be applied to one head type VTR, instead of the two head type VTR. The recording arrangement of Figure 5 and the reproducing arrangement of Figure 8 may be used to correct the tracking error only for the long recording and reproducing operations. Or the arrangements may include a preemphasis circuit and a de-emphasis cirucit the characteristics of which can be changed for then long recording and reproducing operations.

This invention may be applied to different colour television systems such as NTSC system, the PAL system and the SECAM system. Of course, it may be applied to a monochromatic television system.

Moreover, the invention may also be applied to a VTR of the type in which the luminance signal forming the cross-talk component from the adjacent track is suppressed by azimuth loss of the magnetic heads la and Ib which differ from each other in gap inclination, and in which the chrominance signal as the cross-talk component from the adjacent track is eliminated by a comb line filter when the frequency of the chrominance signal is converted to such a frequency that the frequency of the chrominznce signal on a track to be scanned is interleaved with the frequency of the chrominance signal on an adjacent track.

WHAT WE CLAIM IS: 1. A method of recording tracking-error correcting signals added to a video signal on a record medium, said tracking-error correcting signals being for use in detecting errors in the scanning path of a scanning transducer which scans parallel record tracks across said medium, the method comprising: scanning successive record tracks across said medium to record periodic video signals in said record tracks, said video signals containing periodic horizontal synchronizing signals; generating pilot signals during predetermined portions of the horizontal synchronizing signals in said video signals; and recording said pilot signals in said successive tracks such that the position of a pilot signal in one track is shifted with respect to the position of a pilot signal in an adjacent track.

2. A method according to claim 1 wherein said pilot signals are the burst signals included in the horizontal blanking period of said video signal.

3. A method according to claim 1 wherein said pilot signals are added into the horizontal blanking period of said video signal from a pilot signal oscillator on recording.

4. A method according to claim 1, claim 2 or claim 3 further comprising reproducing the recorded signals with the same or a further scanning transducer, separating said pilot signal on said adjacent track from the reproduced signal obtained by scanning said reproducing transducer on said medium, and detecting the relationship between the track to be scanned by said reproducing transducer and the actual scanning trace of said reproducing transducer from the level of said separated pilot signal.

5. A method according to claim 4 wherein said reproduced transducer is supported by a support means responsive to said detection to displace said reproducing transducer transversely with respect to said track to maintain substantial alignment between said reproducing transducer and said track to be scanned.

6. A method according to claim 5 wherein said support means comprises a bi-morph leaf assembly including piezoelectric material.

7. A method according to claim l substantially as hereinbefore described with reference to the accompanying drawings.

**WARNIN

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. by a comb line filter when the frequency of the chrominance signal is converted to such a frequency that the frequency of the chrominznce signal on a track to be scanned is interleaved with the frequency of the chrominance signal on an adjacent track. WHAT WE CLAIM IS:

1. A method of recording tracking-error correcting signals added to a video signal on a record medium, said tracking-error correcting signals being for use in detecting errors in the scanning path of a scanning transducer which scans parallel record tracks across said medium, the method comprising: scanning successive record tracks across said medium to record periodic video signals in said record tracks, said video signals containing periodic horizontal synchronizing signals; generating pilot signals during predetermined portions of the horizontal synchronizing signals in said video signals; and recording said pilot signals in said successive tracks such that the position of a pilot signal in one track is shifted with respect to the position of a pilot signal in an adjacent track.

2. A method according to claim 1 wherein said pilot signals are the burst signals included in the horizontal blanking period of said video signal.

3. A method according to claim 1 wherein said pilot signals are added into the horizontal blanking period of said video signal from a pilot signal oscillator on recording.

4. A method according to claim 1, claim 2 or claim 3 further comprising reproducing the recorded signals with the same or a further scanning transducer, separating said pilot signal on said adjacent track from the reproduced signal obtained by scanning said reproducing transducer on said medium, and detecting the relationship between the track to be scanned by said reproducing transducer and the actual scanning trace of said reproducing transducer from the level of said separated pilot signal.

5. A method according to claim 4 wherein said reproduced transducer is supported by a support means responsive to said detection to displace said reproducing transducer transversely with respect to said track to maintain substantial alignment between said reproducing transducer and said track to be scanned.

6. A method according to claim 5 wherein said support means comprises a bi-morph leaf assembly including piezoelectric material.

7. A method according to claim l substantially as hereinbefore described with reference to the accompanying drawings.