JPS6321976B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a track deviation detection method, in which multiple types of pilot signals with different frequencies for each track are superimposed and recorded on the main information signal, and during playback, a track close to the track to be scanned is detected from the playback signal. The purpose of the present invention is to provide a track deviation detection method that accurately detects the magnitude and direction of track deviation by discriminating each track pilot signal using a variable band filter that is not affected by frequency fluctuations of the pilot signal due to time axis fluctuations. shall be.

In a helical scan type rotary head VTR, there are various problems with the tape running system, such as variations in the tape guide groove formed on the fixed drum, variations in the inclination and height of the poles in the tape running system, and even variations in the mounting location and angle of the fixed drum. The video track inevitably bends due to variations in the mechanism. For this reason, it is clear that the best tracking condition cannot be obtained during compatible playback when playing back on a VTR that is different from the VTR used for recording.In particular, the tape running system has been simplified to reduce costs. In home VTRs, as the recording and reproducing density increases, it is extremely difficult to reproduce while ensuring the required high tracking accuracy.

In addition, conventionally, the distance from the position where the rotating head starts hitting the magnetic tape to the control head may be different between the recorder and the player, and in this case too, the best tracking condition cannot be obtained and the playback signal cannot be adjusted.
It is clear that the SNR becomes worse.

Therefore, in the past, attempts were made to adjust the tracking knob and delay the playback control signal by the required time to perform normal tracking, but this
It is only necessary to control the head scanning locus to move parallel to the longitudinal direction of the recording track of the book, and it is impossible to control the scanning to accurately follow the curve of a single track.

Therefore, in order to perform more accurate tracking control, it is necessary to correct the track deviation by displacing the rotary head using a head moving mechanism in a direction perpendicular to the longitudinal direction of the recording track (in the track width direction). There is.

Conventionally, this method of detecting track deviation involves recording four types of pilot signals with different frequencies superimposed on the main information signal, and distinguishing the pilot signals of the tracks on both sides of the track to be scanned from the reproduced signal during reproduction. There is a method for detecting the track deviation direction and track deviation amount from the relative level difference between these two types of pilot signals. In this case, a band filter that selects the frequency of the pilot signal is required depending on the type of pilot signal, and since the pass frequency band of this band filter is fixed, considering the frequency fluctuation of the pilot signal due to time axis fluctuations such as tape running, There are drawbacks such as the pass band cannot be narrowed very much and a switch is required to select which band filter to use from among these band filters.

The present invention eliminates the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings.

FIG. 1 shows a block system diagram of a recording system using a track deviation detection method according to the present invention. In the figure, a video signal supplied from input terminal 1 is supplied to FM modulator 2 and also to horizontal synchronization signal separation circuit 3, and the horizontal synchronization signal separated by horizontal synchronization signal separation circuit 3 is subjected to phase comparison. It is supplied to the container 4. phase comparator 4, loop filter 5, voltage controlled oscillator 6,
The frequency divider 7 constitutes a phase-locked loop (PLL), and when a head switching pulse is supplied from the input terminal 8 to the control circuit 9, the control circuit 9
switches the control signal and supplies it to the frequency divider 7. Therefore, the frequency divider 7 changes the frequency division ratio to 1/6, 1/9,
1/12, 1/7, 1/10, 1/13, 1/8, 1/
11, 1/6, 1/9, etc., and as a result, the frequency of the output of the voltage controlled oscillator 6 becomes f ₁ where f _H is the frequency of the output of the horizontal synchronizing signal separation circuit 3. =6f _H , f ₂ =9f _H , f ₃ =12f _H , f ₄
The frequencies expressed as = 7f _H , f ₅ = 10f _H , f ₆ = 13f _H , f ₇ = 8f _H , and f ₈ = 11f _H are repeated. This output is supplied as a pilot signal to a mixer 10, where it is mixed with an FM modulated signal and recorded on a magnetic tape 12 by a recording head 11. As shown in FIG. 2, the magnetic tape recorded in this manner is divided into tracks T1, where the pilot signal of frequency _f1 is superimposed on the main information signal, and then tracks _{T2 , T3} ... _T8 , and so on. It is also recorded repeatedly as track _T1 .

The video signal recorded as described above is reproduced by the reproduction system shown in FIG. In the figure, the reproduction signal reproduced by the reproduction head 19 is amplified by the preamplifier 20.
The signal is supplied to the FM demodulation circuit 21 and demodulated into the original video signal. This video signal is output from the output terminal 22 and is also supplied to the horizontal synchronization signal separation circuit 23, where the horizontal synchronization signal is separated and the phase comparator 2
4a and 24b. Here, phase comparator 2
4a, 24b, loop filters 25a, 25b,
Voltage controlled oscillators 26a, 26b, frequency divider 27a,
27b, 1/108 frequency dividers 28a, 28b constitute phase locked loops (PLL) 29a, 29b, and the frequency dividers 27a, 27b are supplied with control signals from the control circuit 30 and set their respective frequency division ratios. 1/
6, 1/9, 1/12, 1/7, 1/10, 1/13,
Choose either 1/8 or 1/11. The control circuit 30 switches the control signal every one track reproduction cycle in synchronization with the rotation of the reproduction head 19. For example, in the first one track reproduction period, the frequency dividers 27a and 27
Instruct frequency division ratios of 1/6 and 1/12 to each of the frequency dividers 27a and 1/9, 1/12, 1/7, 1/10, and 1 thereafter, respectively, in one track reproduction period. /13, 1/
8, 1/11, and the frequency division ratio of the frequency divider 27b is set to 1/7, 1/10, 1/13, 1/8, 1/
11, 1/6, and 1/9, and repeat the above switching control. The frequency of the horizontal synchronization signal is f _H
Then, the frequency of the output of the voltage controlled oscillators 26a, 26b, that is, the phase-locked loops 29a, 29
The frequency of the output of b is f′ ₁ = 6×108f _H , f′ ₂ = 9×
108f _H , f′ ₃ = 12×108f _H , f′ ₄ = 7×108f _H , f′ ₅ = 10
×
108f _H , f′ ₆ = 13×108f _H , f′ ₇ = 8×108f _H , f′ ₈ = 11
×
108f _H and the variable band filter 31,
32 as a clock signal. The variable band filters 31 and 32 pass the harmonic components of the reproduced signal amplified by the preamplifier 20 to the low pass filter 33.
Among those removed by 1/1 of the clock signal frequency,
This is a bandpass filter using a switched capacitor that allows only 108 frequencies to pass.
The outputs of the variable band filters 31 and 32 are level-detected by level detectors 33 and 34, respectively, and supplied to a differential amplifier 35, and a track deviation detection voltage is obtained at an output terminal 36.

For example, when the reproducing head 19 attempts to scan the track _T4 on which the pilot signal of the frequency _f4 is recorded, the frequency dividers 27a and 27b are controlled by the control circuit 30 to set the respective frequency division ratios to 1/12 and 1/12. /
10, and the variable band filters 31 and 32 are supplied with clock signals f' _{3 and f} ' 5 having frequencies f' ₃ =12×108f _H and f' ₅ =10×108f _H , respectively. Ru. Therefore, the variable band filters 31 and 32
Only the pilot signals having the frequencies f ₃ =12f _H and f ₅ =10f _H , ie, the pilot signals recorded on the tracks on both sides of the track to be scanned, are allowed to pass. The pilot signals f ₃ and f ₅ are level detected by level detectors 33 and 34, respectively. For example, when trying to scan track T ₄ as described above, if the reproducing head 19 is tracking normally, the pilot signals of adjacent tracks T ₃ and T ₅ will leak and the level detectors 33 and 34 will be affected. The same amount of output is supplied to the differential amplifier 35, and the output at the output terminal 36 becomes zero. However, playback head 1
9 causes a tracking shift and scans the track 5, there is no output from the level detector 33 and the level detector 35 supplies a large output to the differential amplifier 35.
The track deviation detection voltage at the output terminal 36 becomes negative. Therefore, a track deviation detection power proportional to the amount of track deviation up to one track pitch can be obtained from the output terminal 36, and the direction of track deviation up to two track pitches can also be determined. Furthermore, even if the reproduced signal contains time axis fluctuations such as jitter and the frequency of the pilot signal changes, the passband of the variable band filters 31 and 32 can be changed by the horizontal synchronization signal separated from the same reproduced signal that reproduced the pilot signal. is determined, the pass band of the variable band filter can be narrowed without being affected by time axis fluctuations.

FIG. 4 shows a second embodiment of the reproduction system of the track deviation detection method according to the present invention. In the figure, the same components as those in FIG. 3 are given the same reference numerals, and their explanations will be omitted. The phase locked loops 37a and 37b are the phase locked loop 29 shown in the first embodiment.
It is constructed in the same manner as a and 29b, and is supplied with a horizontal synchronizing signal, and is supplied with a control signal from a control circuit 39, and supplies a clock signal to variable band filters 40 and 141, which are band pass filters using switched capacitors.

Similarly to the control circuit 30, the control circuit 39 also switches control signals every one track reproduction period. For example, in the first one track reproduction cycle, the phase locked loops 37a, 29a, 29b, and 37b are instructed to have a frequency division ratio of 1/11, 1/6, 1/12, and 1/7, respectively;
Thereafter, the frequency division ratio of the phase locked loop 37a is changed to 1/6, 1/9, 1/12, etc. in one track reproduction period.
1/7, 1/10, and 1/8, and set the frequency division ratio of the phase locked loop 29a to 1/9,
1/12, 1/7, 1/10, 1/13, 1/8, 1/
11, and set the frequency division ratio of the phase-locked loop 29b to 1/7, 1/10, 1/13, 1/
8, 1/11, 1/6, and 1/9, and set the frequency division ratio of the phase-locked loop 37b to 1/9.
10, 1/13, 1/8, 1/11, 1/6, 1/9,
Switch in the order of 1/12 and repeat the above switching control.

The outputs of the variable band filters 31 and 32 are attenuated by attenuators 42 and 43, respectively, and then sent to the level detector 3.
3 and 34 are level detected and supplied to one input terminal of adders 44 and 45, respectively, and the outputs of variable band filters 40 and 41 are level detected by level detector 4.
6, 47, adders 44, 4
5, respectively. The outputs of adders 44 and 45 are respectively supplied to a differential amplifier 35, and a track deviation detection voltage is obtained at an output terminal 36.

For example, when trying to scan track _T4 , the phase locked loops 29a, 29b,
37a and 37b have their respective frequencies f′ ₃ =12×108f _H and f′ ₅ =10 by control signals from the control circuit 39.
×108f _H , f′ ₂ =9×108f _H , f′ ₆ =13×108f _H are passed through variable band filters 31 and 3.
2, 40, 41, and these variable band filters 31, 32, 40, 41 each have a frequency f ₃ =
Only pilot signals represented by 12f _H , f ₅ =10f _H , f ₂ =9f _H and f ₆ =13f _H , that is, pilot signals recorded on two tracks on each side of the track to be scanned, are allowed to pass. Outputs f ₃ and f ₅ of these pilot signals from the variable band filters 31 and 32 are attenuated by attenuators 42 and 43, respectively, and then level detected by level detectors 33 and 34 and supplied to an adder 44. Further, the outputs f ₂ and f ₆ of the variable band filters 40 and 41 are level-detected by level detectors 46 and 47 without being attenuated, respectively, and then outputted to an adder 4.
4,45.

Therefore, when trying to scan track T ₄ ,
If the playback head 19 is normally tracking the track T ₄ , the same amount of level detection outputs of the pilot signals f ₃ and f ₅ are supplied to the adders 44 and 45 , and the tracks T ₂ and T ₆ are tracked by the playback head 19 . There is no output from the variable band filters 40 and 41 since the track shift detection voltage at the output terminal 36 becomes zero. However, when the reproduction head 19 causes a tracking error and scans the track _T5 , there are no outputs from the variable band filters 31 and 40, and the large output of the variable band filter 32 is attenuated and level detected, and the small output of the variable band filter 41 is detected. is added together with the level-detected signal in an adder 45,
A negative track deviation detection voltage is obtained at the output terminal 36. Further, when the reproduction head 19 causes a tracking error and scans the track _T6 , there is no output from the variable band filters 31 and 40, and the variable band filter 32
The small output of is attenuated and level detected,
The large output of the variable band filter 41 is added together with the level-detected output in the adder 45, and output to the output terminal 36, which is negative and has a larger absolute value than when the reproducing head 19 is scanning the track _T5 . Detection voltage can be obtained. Therefore, if the attenuation amounts of the attenuators 42 and 43 are appropriately determined, a track deviation detection voltage proportional to the amount of track deviation up to 2 track pitches can be obtained from the output terminal 36, and the direction of track deviation up to 3 track pitches can be obtained. I understand.

By adding a pair of phase-locked loops, variable band filters, and attenuators to the embodiment shown in FIG. 4, it is possible to obtain a track deviation detection voltage proportional to the amount of track deviation up to 3 track pitches. Furthermore, if the types of pilot signals are increased during recording, it is possible to obtain a track deviation detection voltage proportional to the amount of track deviation even in the case of a larger track deviation in the same manner as described above. Further, the attenuators 42 and 43 are the level detector 33,
34 and adders 44 and 45.

In each of the above embodiments, the variable band filter is a band pass filter using a switched capacitor that passes only the frequency of 1/108 of the clock signal. The 1/108 frequency divider in the phase-locked loop may be correspondingly changed to a frequency divider with another frequency division ratio using a passing switched capacitor bandpass filter. Further, this variable band filter does not use a switched capacitor, but may use a charge transfer element such as a bucket brigade device (BBD) or a charge coupled device (CCD).

As described above, the track deviation detection method according to the present invention sequentially repeats pilot signals f ₁ , f ₂ , ..., f _n (m is an integer of 3 or more) having different frequencies for each track and superimposes them on the main information signal. and record the pilot signal f _i (i is an integer, 1≦i≦m, where f _p =
f _n , f _n+1 = f ₁ ),
By supplying this reproduced signal to a variable band filter means to select the frequency of at least the pilot signals f _i-1 and f _i+1 , and comparing the level detection outputs of the pilot signals f _i-1 and f _i+1. There is no need to prepare a band filter for each pilot signal in order to detect track deviation. In addition, since the variable band filter determines its pass frequency band by the horizontal synchronization signal separated from the reproduced signal, even if the frequency of the pilot signal changes due to fluctuations in the time axis, the pass frequency band of the variable band filter changes accordingly. This pass frequency band can be sufficiently narrowed, a more accurate track deviation detection voltage can be obtained than the conventional one having a fixed frequency band, and a switch for selecting a band filter can be eliminated. Moreover, the variable band filter has at least the pilot signal fi _-1 ,
To select frequencies f _i+1 , f _i+j (j is an integer, |j|≧2) and compare the level detection outputs of these pilot signals f _i-1 , f _i+1 , f _i+j It has the advantage of being able to determine the magnitude and direction of a large track shift of more than twice the track pitch that occurs during high-speed playback.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of a recording system using the track deviation detection method according to the present invention, FIG. FIG. 4 is a block system diagram of a first embodiment of a reproduction system using a track deviation detection method according to the invention, and FIG. 4 is a block system diagram of a second embodiment of a reproduction system using a track deviation detection method according to the invention. 1, 8...Input terminal, 2...FM modulator, 3, 23
...Horizontal synchronization signal separation circuit, 4, 24a, 24b...
Phase comparator, 5, 25a, 25b... Loop filter, 6, 26a, 26b... Voltage controlled oscillator, 7,
27a, 27b... Frequency divider, 9, 30, 39... Control circuit, 10... Mixer, 11... Recording head, 12...
Magnetic tape, 19... Reproduction head, 20... Preamplifier, 21... FM demodulator, 22, 36... Output terminal,
29a, 29b, 37a, 37b... Phase locked loop, 31, 32, 40, 41... Variable band filter, 33, 34, 46, 47... Level detector, 35... Differential amplifier, 42, 43... Attenuator, 4
4, 45...Adder.

Claims (1)

[Scope of Claims] 1. In a track deviation detection method for a rotary head that reproduces signals recorded on tracks inclined with respect to the longitudinal direction of a magnetic tape, pilot signals f ₁ , f ₂ , . . . having different frequencies for each track are used. fm(m
is an integer of 3 or more) are repeated in order and recorded superimposed on the main information signal, and the pilot signal f _i (i is an integer,
1≦i≦m, where f _p = f _n , f _n+1 = f ₁ ) is reproduced, and this reproduced signal is supplied to a variable band filter means to obtain at least the pilot signal fi _-1. , f _i+1 and select the frequency of the pilot signal
A track deviation detection method characterized by detecting a track deviation by comparing level detection outputs of f _i-1 and f _i+1 . 2 The variable band filter means at least filters the pilot signals f _i-1 , f _i+1 , f _i+j (j is an integer, |j|≧
2), select the frequency of the pilot signal fi _-1 ,
2. The track deviation detection method according to claim ₁ , wherein track deviation is detected by comparing level detection outputs of f i+1 and f _i+j .