Abstract:
A tracking control apparatus is capable of decreasing sufficiently the effects of crosstalks in effectively utilizing the azimuth angle by tracking controlling the magnetic head in order that the scanning position of the magnetic head will be deviated to the prescribed direction and quantity. In case of tracking controlling the magnetic head depending upon the first and second error signals formed in order to correspond to the frequency difference element between the pilot signal of the adjacent recording track and the pilot signal of the scanning recording track, since the first and second error signals are to be weighted with the prescribed ratio, the scanning position of the magnetic head can be deviated to the position where the crosstalk of the reproducing signals can be sufficiently decreased for practical use.

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     This invention relates to a tracking controlling apparatus, and more particularly to improvement of a data recording/reproducing apparatus using an automatic track following system, in which a recorded pilot signal is reproduced from a data recording track formed on a recording medium by a reproducing head which is controlled to track to a reproducing track based on the reproduced pilot signal. 
     DESCRIPTION OF THE PRIOR ART 
     Conventionally, in a data recording/reproducing apparatus, for example, a digital video tape recorder, recording tracks are helically formed to successively on a magnetic tape by use of a magnetic head mounted on a rotary drum. In a digital video tape recorder using an azimuth recording method, recording tracks are successively formed by alternately using a plurality of magnetic heads with different angles, to reduce an influence by crosstalk signals obtained from adjacent tracks in reproducing. 
     Tracking control in a digital video tape recorders uses an automatic tracking following system (ATF system), as disclosed in U.S. Pat. Nos. 4,594,615 and 4,658,309. The ATF system is one of the phase servo systems in a capstan control system of a digital video tape recorder. For example, four pilot signals different in frequency from each other are cyclically recorded with video information on recording tracks, and a tracking control signal is obtained by detecting a difference between the pilot signals picked up from adjacent tracks in reproducing a data signal, so that the tracking control is executed by using the tracking control signal. 
     That is, as shown in FIG. 1, a magnetic head 1 detects pilot signals f1 and f3 which are recorded on recording tracks TA preceding and following from the recording track to be tracked in the reproducing mode. 
     The signal levels of detected pilot signals f1 and f3 are proportioned to values of protruding widths x1 and x2 toward the preceding and following tracks TA. 
     As a result, the digital video tape recorder tracking-controls the magnetic head 1 so as to make signal levels of the pilot signal f1 and f3 equal to each other position. Thus, the magnetic head 1 becomes locked in a tracking. 
     As a result, in such a conventional tracking control system, the magnetic head 1 is controlled to protrude to the preceding and following tracks equally, so that the center of the magnetic head 1 traces sequentially the center portion of the recording tracks. Therefore, the conventional tracking control system has a disadvantage that it cannot minimize an influence of crosstalk from the video signals of the adjacent tracks. 
     The above method can easily make the magnetic head track precisely trace to the center of each of the recording tracks, but it is difficult for the reproducing head to track in a lock position and deviate from each of the recording tracks when necessary, when in tracking the reproducing head to a desired track in after-recording, or when in measuring an amount of crosstalk to an amount of tracking deviation in adjusting a video tape recorder. 
     U.S. Pat. No. 4,658,309, discloses a tracking control apparatus of an ATF system which can be easily made to deviate from a tracking lock point. 
     In this Patent, the pilot signals of tracks adjacent to each other are detected, in reproducing the data signal. First and second error signals are obtained from detected pilot signals. Each obtained error signal is multiplied by coefficient n. The obtained error signal and coefficient n multiplied error signal are selected by means of corresponding switching circuits, which select either the first and second error signals when tracking, or the coefficient n multiplied error signal, obtained from the track of opposite direction against the direction to be deviated, when tracking from the lock position to the deviated position. 
     However, with the above tracking control apparatus which can deviate from a tracking lock point, the tracking lock point is deviated by merely multiplying the error signal by a weighting coefficient as occasion demands, but it cannot minimize an influence of crosstalk of video signals obtained from adjacent tracks. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of this invention is to provide a tracking control apparatus of an information recording/reproducing system in which a magnetic head is tracking-controlled so as to deviate the scanning position of the magnetic head in a predetermined direction by a predetermined amount, and the effects of crosstalks is effectively reduced by utilizing an azimuth angle. 
     The foregoing objects and other objects of the invention have been achieved by the provision of the tracking control apparatus 1 and 40 in which the first and second error signals S11 and S12 are formed corresponding to the differential frequency elements ΔfA and ΔfB denoting the difference between the frequency of pilot signals f1 to f4 obtained from recording tracks TA or TB to be scanned and between the frequency of pilot signals f1 to f4 obtained from the recording tracks TB or TA adjacent to the both sides of said recording tracks TA or TB to be scanned, by successively scanning by means of magnetic head 1A and 1B the recording tracks TA and TB formed helically to arrange successively in a longitudinal direction on the magnetic recording medium 2 and between the recorded pilot signals f1 to f4 of different frequencies. Tracking error signal S13 is generated for tracking-controlling the magnetic heads 1B and 1A so as not to produce differences between the first and second error signals S11 and S12, wherein: the magnetic heads 1 and 1A have wider head widths than the widths of recording tracks of TA and TB, and said first and second error signals are weighted by error signal weighting means with the prescribed ratio K1 and K2, to make said magnetic head move to desired tracking position, whereby the scanning positions of the magnetic heads 1A and 1B to recording tracks TA and TB is made to deviate by a deviation amount and for a deviation direction determined on the basis of predetermined ratios K1 and K2. 
     The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic diagram illustrating a trace condition of the reproducing head 1 according to the conventional tracking control; 
     FIG. 2 is a schematic diagram illustrating a tracking error signal forming system according to one embodiment of the present invention; 
     FIG. 3 is a schematic diagram showing a trace condition of the reproducing head 1 according to the tracking control of the present invention; 
     FIG. 4 is a correlation diagram showing the relation between conversion rates K1 and K2; 
     FIG. 5 is a characteristic curve showing the protruded width of the reproducing head 1 and the azimuth loss thereof; 
     FIG. 6 is a block diagram showing a tracking error signal forming system according to the second embodiment; and 
     FIG. 7 is a block diagram showing modifications of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of this invention will be described with reference to the accompanying drawings: 
     (1) First Embodiment 
     In FIGS. 2 and 3 in which the identical reference numerals are given with the corresponding parts of FIG. 1. Numeral 10 generally designates a digital video tape recorder having first and second exclusively reproducing heads 1 with wider head width as compared with the recording head. 
     In the first and second reproducing heads, the reproducing tracks which are helically formed successively on the magnetic tape will be alternately traced. 
     After a part of the picture data reproduced from a tape 2 by the first reproducing head 1 is supplied to a pilot signal detection circuit 11 as a reproducing output signal S1, the pilot signal element is extracted as a reproducing pilot signal S2 and is supplied to a multiplier 21 of the error forming circuit 12 as the first multiplying input. 
     At this point, as shown in FIG. 3, four kinds of pilot signals f1 to f4 with different frequencies are recorded on each recording track of the tape 2 with the video signals successively in a cyclic manner. 
     The pilot signals f1 to f4 will be selected at the value to satisfy the following equations: 
     
         ΔfA=|f.sub.1 -f.sub.2 |=|f.sub.3 -f.sub.4 |                                                (1) 
    
     
         ΔfB=|f.sub.2 -f.sub.3 |=|f.sub.1 -f.sub.4 |                                                (2) 
    
     and thus, the difference frequencies of pilot signal elements between the preceding and following tracks are arranged to become ΔfA and ΔfB respectively. 
     A reference signal having the same frequency as those of the pilot signal f1 or f3 of the objective track TA as a reference pilot signal S3 is supplied from a reference signal generation circuit 13 to a multiplier 21 as a second multiplying input. 
     With this arrangement, the multiplier 21 obtains a multiplying output signal S10 comprising different frequencies ΔfA and ΔfB respectively, and supplies to the first and second difference frequency detection circuits 22 and 25 respectively. 
     The first difference frequency detection circuit 22 extracts the signal element of the difference frequency ΔfA from the multiplying output signal S10 and after supplying this to a rectifying circuit 23 and converting to a DC level error signal S11, supplies to a first weighting circuit 24. 
     Similarly, the second difference frequency detection circuit 25 extracts the signal element of the difference frequency ΔfB from the multiplying output signal S10 and after supplying to a rectifying circuit 26 and converting to a DC level second error signal S12, supplies to a second weighting circuit 27. 
     Moreover, the weighting circuits 24 and 27, upon level shifting the signal levels of the first and second error signals S11 and S12 to the prescribed respective weighting ratios K1 and K2 times, output to a subtraction circuit 28. 
     The weighting ratios K1 and K2, as shown in FIG. 4, can be variable within the range of 0 to 1 and the sum will be 1. 
     With this arrangement, the subtracter 28 obtains a tracking error signal S13 which becomes 0 level at the time when K1 times the signal level of difference frequency ΔfA is equal to K2 times the signal level of the difference frequency ΔfB by subtracting the signal level of the second error signal S12 from the signal level of the first error signal S11, and outputs to a phase servo circuit (not shown in figure) of a capstan servo loop as a corrective signal via an output amplifier 29. 
     With this arrangement, in the digital video tape recorder 10, the phase servo circuit controls the running speed of the magnetic tape 2 in order that the ratio of protruded widths x1 and x2, x1: x2, will be equal to the weighting ratio K2 and K1, K2: K1. 
     In case of this embodiment, in the digital video tape recorder 10, it is arranged that the weighting ratio K1 becomes larger than the weighting ratio K2, and thus the magnetic head 1 will be deviated toward the preceding track side, i.e., offsetted. 
     In this case, the azimuth loss L of the data signal obtained from the preceding track can be expressed as the following equation: ##EQU1## where, the azimuth angle of the first and second heads is θ, and the recording wavelength of respective pilot signals is λ. 
     Accordingly, in the case where the azimuth angle is small, using the following equation: 
     
         tan θ≃sin θδθ        (4) 
    
     the equation (3) can approximate to the following: ##EQU2## 
     Accordingly, there is a relationship between the azimuth loss Ec and the value of following equation ##EQU3## as shown in FIG. 5 with a characteristic curve, that generally the azimuth loss L will be larger as the protruded width x2 becomes larger, when, the azimuth angle θ is constant. 
     Accordingly, in this case, the head 1 is offset in order to make the protruded width x1 toward the following track as small as possible and make the protruded width x2 toward the preceding track as large as possible, therefore the quantity of crosstalk from the preceding track will be larger and the quantity of crosstalk from the following track will be decreased as compared with the state of the centered fixed tracking position. Thus, as a whole, the crosstalk from the adjacent track can be decreased as compared with the fixed tracking position. 
     However, realistically the curvatures occur on the recording tracks depend upon the drum span of the rotary drum and processing precision, etc. Therefore, the of protruding width x1 will be determined by how much marginal tracking errors will be afforded, and it follows that the protruding widths x1 and x2 have limits. 
     Accordingly, in this embodiment as shown in FIG. 5, if the following equation: ##EQU4## is an integer number, in utilizing that the azimuth loss L gets to the maximum value (hereinafter referred to null point), the value of weighting ratios K1 and K2 will be set in order that .sup.⊖ x 2  /λ=1 gets nearer to the first Null point as possible, i.e., the x 2  /λ=1 gets as close as possible to the valve 1. 
     According to the foregoing construction, the pilot signal detection circuit 11 extracts the pilot signal element from the reproducing signal to be outputted from the magnetic head 1 and supplies to the difference frequency detection circuits 22 and 25 as the multiplying output signal S10 via the multiplier 21. 
     The difference frequency detection circuits 22 and 25, after extracting the difference frequency ΔfA and ΔfB elements from the multiplying output signal S10, respectively, supply error signals S11 and S12 to the respective weighting circuits 24 and 27 via the rectifying circuits 23 and 26. The weighting circuits 24 and 27 output the error signals S11 and S12 level shifted by K1 and K2 times to the subtraction circuit 28. 
     The subtracting circuit 28 subtracts the weighted error signal S12 from the weighted error signal S11 and at the time when K1 times of the signal level of difference frequency ΔfA and K2 times of the signal level of the difference frequency ΔfB become equal. Thereafter, subtraction circuit 28 supplies the tracking error signal S13 which would come to the 0 level, to the phase servo circuit of the capstan servo loop via the output amplifier 29. 
     With this arrangement, the phase servo controls the running speed of the magnetic tape 2 in order that the ratio x1:x2 which are the protruding widths toward the preceding and following tracks x1 and x2 of the magnetic head 1 becomes equal to the inverse ratio K2:K1 of the weighting ratio K1 and K2 depending upon said tracking error signal S13; and thus, the crosstalk quantity from the adjacent tracks can be decreased as compared with the centered fixed tracking position. 
     (2) Second Embodiment 
     In FIG. 6 wherein corresponding parts of FIG. 2 are given the same reference numerals with 40 generally shows a digital video tape recorder according to the second embodiment having the first and second error signal forming circuits 12 and 12A. 
     The first error signal forming circuit 12, as described above in FIG. 1, after forming the first tracking error signal S13 depending upon the reproducing output signal to be outputted via the first reproducing head, outputs to the output amplifier 29. 
     On the other hand, the second error signal forming circuit 12A which is constituted by the same construction as to those of the first error signal forming circuit 12, forms the second tracking error signal S13A depending on the reproducing output signal S1A to be outputted via the second reproducing head 1A and outputs to the output amplifier 29. 
     According to the construction of the second embodiment in FIG. 6, since the tracking control signal will be generated depending upon the pilot signals to be obtained respectively from two magnetic heads which are alternately scanning, the preciseness in tracking can be further improved as compared with the case of tracking controlling by one magnetic head. 
     (3) Other Embodiments 
     The first and second embodiments described above have dealt with the case of applying the present invention to the digital video tape recorders 10 and 40 having the exclusively reproducing heads 1 and 1A. However, the present invention is not only limited to the above but also suitably applied to the digital video tape recorder having the magnetic head which can be used both in reproducing and recording. 
     Furthermore, the first and second embodiments described above have dealt with the case of applying the present invention to the digital video tape recorder. However, the present invention is not only limited to the above but also widely applicable to the magnetic reproducing apparatus which reproduces various signals from the recording tracks formed on the magnetic tape. 
     Moreover, the first and second embodiments described above have delay with the case of offsetting the magnetic head toward the preceding side. The present invention is not, however, only limited to the above but the same effect can be achieved if the magnetic head is offsetted toward the succeeding side. 
     Furthermore, the first and second embodiments described above have dealt with the case of weighting the error signals S11 and S12 in utilizing the weighting circuits 24 and 27. The present invention is not, however, only limited to the above but the rectifying circuits 23 and 26 may be connected with the variable resistance 50 as shown in FIG. 7. 
     Furthermore, the pilot signal recorded in each track, is may be recorded to every portion on the recording track. 
     While there has been described in connection with the preferred embodiments of the invention, it sill be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of the invention.