JPH0466041B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for displaying track curvature of a magnetic recording/reproducing apparatus (hereinafter simply referred to as a VTR). Conventional configuration and its problems In a two-head helical scan VTR, one image is recorded on a magnetic tape as one recording track. In this case, the recording track should originally be recorded in a straight line, but in reality it is recorded in a curved line due to variations in the mechanical accuracy of the tape running system. If a VTR is manufactured with each deck having its own unique curvature, for example, a tape recorded on a VTR with a curvature of A can be changed to a tape with a curvature of B.
During compatible playback on a VTR, the playback head mistracks and scans the playback by an amount corresponding to the difference in curvature between the two decks. As a result, the reproduced image quality deteriorates by the amount of mistracking. When manufacturing VTRs, the track curvature of each deck is adjusted so that the track curvature of each deck is below a certain value in order to solve the above-mentioned problem during compatible playback. The method is to play back a master tape on which a track is recorded in a straight line, obtain a signal indicating track curvature (described later) from the playback signal, and use limiter posts located on both sides of a cylinder with a built-in rotating head to run the tape. raise and lower the height,
Adjust so that the track curvature of that deck is below a certain value. Since track bending cannot be reduced to zero,
Although some mistracks occur during compatible playback, deterioration in image quality due to mistracks is prevented by using a head that is wider than the track pitch. VTRs such as the VHS (trademark) system use changes in the envelope of the reproduced luminance signal as a signal indicating track curvature. This method will be explained. FIG. 1 is a diagram showing the scanning positions of the recording track and the reproducing head, and FIG. 2 is a diagram showing the waveform of the reproduction luminance signal obtained when the head scans each scanning position. In FIG. 1, A ₁ , B ₁ , A ₂ indicate recording tracks, and Ai (i=1, 2, 3, . . . ) and Bi tracks are recorded by heads having different azimuth angles. Each recording track is depicted as curved at the point where the head begins contacting the tape (lower side on the page). 2, 3, 4 are
B shows a head with the same azimuth angle as the signal recorded on track _A1 , mistracked to A1 side, ontracked to _A1 side, respectively.
A shows a mistracked state on _{the 2} side. The head scans linearly in the direction indicated by arrow 1. The reproduction level of the luminance signal is proportional to the width of the track scanned by the head. In FIG. 1, it is proportional to the width of the head on the track _B1 of the same azimuth. Therefore, the luminance signal obtained when the head scans the position 2 has the waveform shown in FIG. As is clear from the track curvature shown in FIG. 1 and the waveform change shown in FIG. 2, the change in the output of the luminance signal obtained when mistracking left and right from the on-track position corresponds to the track curvature. If the track is a straight line, both on-track and mistrack will have the waveform shown in b. From FIGS. 1 and 2, one may think that track bending can be determined by looking only at the waveform c, for example, without looking at the waveforms a, b, and c, but this is actually incorrect. This is because when the head starts contacting the tape, the head touch is generally poor and output is difficult to output. Therefore, with such a deck, the output will have the waveform c even if there is no track bend. At this time,
Even when mistracked to the opposite side, the output is c
The waveform will be similar to . From this, it can be said that the change in the output waveform when mistracking left and right corresponds to track bending. The above is an explanation of the conventional method. To summarize the procedure, turn the tracking volume to mistrack to one side, and memorize the waveform of the reproduced output at that time. Next, mistrack to the opposite side, look at the waveform of the playback output at that time, and make running adjustments by looking at the amount of change in both outputs. In conventional VTRs that use control signals to perform tracking control during playback, the above method of adjusting track curvature has been sufficient. but,
Recently, a tracking control method that does not use control signals has been proposed and adopted as a unified standard for 8mm VTRs. In this method, four types of pilot signals are sequentially recorded for each field, and during playback, tracking control is performed using crosstalk signals that are played back from adjacent tracks located on both sides of the track to be played. The on-track position is when the levels of crosstalk signals reproduced from the track are equal. Such a control system does not require a conventional tracking volume. Also, it is difficult to easily shift the tracking like with conventional VTRs. For this reason, it is difficult to apply the conventional method of determining track bending by mistracking. In addition, the conventional method requires the operation of turning the tracking volume, which has the disadvantage of lengthening the process time. OBJECTS OF THE INVENTION A first object of the present invention is to provide an apparatus that allows track bending to be directly observed on an oscilloscope in an on-track state, and allows track bending to be adjusted without mistracking as in the prior art. A second object of the present invention is to provide an apparatus for displaying track curvature without being affected by the reproduction output sensitivity of the head. Structure of the Invention In the present invention, only one type of pilot signal for tracking control is extracted from four types of recorded pilot signals, and the pilot signal obtained when the tracks before and after the track on which the pilot signal is recorded is reproduced and scanned. This device is configured to detect track bending from the difference signal between the output waveforms of the signals. In addition, in order to correct the influence of the playback output sensitivity of the head, the playback pilot signal is passed through an AGC circuit (automatic gain adjustment circuit), one type of pilot signal different from the above is extracted, and this pilot signal is recorded. The AGC circuit is configured to operate so that the reproduction level of the pilot signal obtained when the track is reproduced and scanned is constant. Description of Examples Examples of the present invention will be described below. FIG. 3 shows the recording track on which the pilot signal was recorded. B ₁ , A ₁ , B ₂ . . . indicate recording tracks recorded by heads A and B having different azimuth angles, and the tracks have a curve at the position where the heads start contacting the tape. On each recording track, each pilot signal indicated by f ₁ to _{f 4} is recorded together with a video signal, and each pilot signal is continuous within one recording track. The signals indicated by f ₁ to _{f 4} have the frequencies shown in Table 1.

[Table] Since each pilot signal is a relatively low frequency signal, the loss due to the azimuth effect is negligibly small. Therefore, even if the Ai (i=1, 2, 3, . . . ) track is reproduced by B heads having different azimuth angles, the pilot signal can be reproduced with almost no loss. Furthermore, even if the head does not reproduce the adjacent track, it is possible to reproduce the pilot signal recorded on the adjacent track as a crosstalk signal. In FIG. 3, numeral 5 indicates the head on track on the _A1 track. The head reproduces and scans the recording track in the order of B ₁ , A ₁ , B ₂ , A ₂ . At this time, if only the _f1 signal is extracted from the reproduced pilot signal using a tuned amplifier or the like, the signal shown in FIG. 4 can be obtained.
In the figure, a indicates a head switching signal, and B ₁ , A ₁ . . . shown in figure a indicate the time timing during which the head is on-tracking on the track. When the head plays on B ₁ track, A ₁
Played on the head partially covered by the track
The _f1 signal or the _f1 signal reproduced as a crosstalk signal reaches its maximum at the point where the head starts contacting the tape, as shown in Figure b. The head is
A When playing back _one track, almost the same level of playback signal is obtained. When playing back on the _B2 track, the waveform shown in figure b is obtained from the head or crosstalk signal that is partially applied to the _A1 track. In other words, the playback level is the lowest at the point where the head starts contacting the tape. When the head scans the _A2 track, it is farthest from the track recording _f1 , so the reproduction output is almost zero. Hereinafter, the waveforms shown in figure b can be obtained for B ₃ , A ₃ , . . . using the same concept. f ₁ reproduced during periods B ₁ and B ₂ shown in Figure 4b
The waveform of the reproduced signal is the same as the output waveform of the luminance signal already explained using FIG. Therefore, the fourth
The difference in the envelopes of the respective output signals reproduced during periods _B1 and _B2 shown in the figure corresponds to track curvature. The need to see the difference is necessary in order to separate the effects of head touch from track bending, which was already mentioned in the description of the luminance signal. The waveforms of FIG. 4b can be viewed superimposed on an oscilloscope as shown in FIG. Fifth
In the figure, a is a head switching signal, and b is a signal obtained by detecting and rectifying the signal in FIG. 4b and superimposing it on an oscilloscope. Needless to say, the signals in Figure 5 a and b are displayed on the oscilloscope at the same time, and
This can be easily achieved by triggering the oscilloscope with the signal a. Signals 6 and 7 shown in Fig. 5b indicate the track bend each time during the track bend adjustment period, so it is possible to see the track bend in real time without turning the tracking shifter as in the conventional case. can. If the track curvature is adjusted so that the waveforms 6 and 7 are parallel, the scanning locus of the head scans the magnetic tape to form a substantially straight recording track. FIG. 6 shows an example of a specific circuit for obtaining the above waveform. In the figure, a reproduction pilot signal is inputted from a terminal 8. 9 is a tuned amplifier that extracts only the _f1 signal, and 10 is a detection rectifier circuit. The waveform shown in FIG. 5b is obtained at the terminal 11,
This signal is fed to an oscilloscope. FIG. 7 shows a second specific embodiment of the invention. In the figure, the regenerated pilot signal input from the terminal 12 is sent to the _f1 tuned amplifier 13 and the detection rectifier circuit 1.
4, a signal similar to that shown in FIG. 6 is taken out. Reference numeral 15 denotes a sample and hold circuit, which divides one field into 1/16, for example, and samples and holds the signal of the circuit 14. The held signal is A/D converted by an analog-to-digital conversion circuit 16 and then stored digitally. Reference numeral 17 denotes a one-frame delay circuit, which outputs a signal representing the difference between the signal currently being reproduced by the circuit 18 and the signal one frame before.
After this signal is D/A converted by the digital-to-analog conversion circuit 19, it is taken out at the terminal 20 in the form of an analog signal. Therefore, a signal representing the difference between the B ₁ and B ₂ periods shown in FIG. 4 is outputted to the terminal 20, and this signal indicates track bending. That is, as explained with reference to FIG. 5B, there is no need to superimpose the two signals on the oscilloscope, and it is sufficient to adjust the track curvature so that the signal taken out from the terminal 20 becomes a straight line. Note that the circuits 17 and 18 can be realized using a microcomputer or the like. Furthermore, in reality, it is necessary to align the polarities of the signals output from the terminals 20. That is,
In FIG. 4, B ₁ period signal − B ₂ period signal,
B When outputting a _3- period signal - B _{a 4-} period signal
B ₂ period signal - B ₃ period signal must not be output. Although this method is not shown, it is easy to determine the polarity of the subtraction by using an AND gate between the head switching signal and a signal obtained by dividing the frequency of the head switching signal by 1/2. Next, the effects of various head variations on the accuracy of track bend display according to the present invention will be explained. Fig. 8 shows each recording track of B ₁ , A ₁ , B ₂ and f ₄ ,
The pilot signals of f ₁ and f ₂ and the scanning position of each head are shown. 21 indicates the regular A head, 22-2
5 indicates the B head. 22 is the regular B head, 2
3 is a B head whose installation height is shifted relative to A, 24 is a B head that is wider than a normal head, and 25 is a B head whose shape and scanning position are normal, but the head is A B head is shown whose reproduction output sensitivity is greater than that of the regular head. 9th
In the figure, the waveforms of the _f1 signals reproduced by heads 22 to 25 are shown corresponding to b to e. In FIG. 9, a shows the head switching signal, solid line waveforms b to e show the levels reproduced by a regular head, and dotted lines show signal waveforms when reproduced by heads with various variations. When the _B1 track is reproduced by the head 23, the reproduction level of _f1 is higher than the normal level, as shown by the dotted line in FIG. 9c. Furthermore, when the _B2 track is reproduced by the head 23, the reproduction level of _f1 is lower than the normal output level. Since the head that plays back the _A1 track is always head 21, the waveform shown in FIG. 9c is obtained. In a similar way, the signal reproduced by the head 24 can be considered, and the reproduction level of f ₁ obtained when scanning the B ₁ and B ₂ tracks will be higher than the normal level. In FIG. 9e, the B head has a higher reproduction output sensitivity than the regular head, so the reproduction level of f ₁ obtained when scanning the B ₁ and B ₂ tracks is higher than the regular level. With the above, we were able to understand the f ₁ playback level due to variations in various heads, but
When displaying track bending, the problem is not its absolute level but its variation. That is, the amount of change when each head is slightly shifted to the left or right on the paper from the scanning position shown in FIG. 8 is the accuracy for displaying track curvature. The amount of change is the same for each head scan shown by 22 to 24, but the amount of change is different for heads whose reproduction sensitivities are different from the normal head. For example, as shown in this example, if the reproduction sensitivity is large, the amount of change for a given amount of track deviation will also be large. Therefore, if the accuracy of the jig circuit for displaying track bending is to be improved, correction based on the difference in reproduction sensitivity of the heads is required. A second object of the present invention is to provide a method for solving the above problems. The method will be explained below. FIG. 10 shows the recording state of each recording track B ₁ , A ₁ , . . . and the pilot signals f ₄ to _{f 3} . 2
6 is the A head, and 27 is the B head, both of which have normal shapes and scanning positions as shown in the figure. It is assumed that the reproduction sensitivity of the A head 26 is normal and that of the B head 27 is higher than the normal reproduction sensitivity. FIG. 11 shows waveforms obtained by extracting only f ₁ and f ₂ in this state. In the figure, a represents the head switching signal, b represents the reproduction output of _f1 , and c
shows the reproduction output of _f2 . In b and c,
The solid lines indicate each output from a regular head, and the broken lines indicate the reproduction level when reproduced by a head with high reproduction sensitivity. In other words, B with high playback sensitivity
Only the f ₁ and f ₂ signals reproduced by the head are output higher than the normal reproduction level. The part that displays track bending is B ₁ and B ₂ if the signal is f ₁ .
is the period of the head switching signal denoted by f ₂
If the signal is , the period is A ₁ and A ₂ . Therefore,
The _{B2 period} of f2 is irrelevant to the display of track bending. As is clear from Fig. 11, the reproduction output increases for both f ₁ and f ₂ when B _i (i=1, 2,
...) only during the period when the track is being scanned.
This is natural because only the B head has high reproduction sensitivity, but therefore f ₁ reproduced in the B head
It can be said that the rate at which _f2 increases is the same as the rate at which f2 increases. Therefore, only f ₂ scanned by the B head is extracted, and the larger level of f ₂ (in FIG. 11, B ₂
By controlling the level of the reproduction pilot signal so that the period) is constant, it is possible to correct variations in the reproduction sensitivity of the heads. FIG. 12 shows a specific circuit example. In the same figure,
A reproduction pilot signal is input from the terminal 28. 29 is an AGC circuit which changes the amplification factor of the reproduction pilot so that the level of the signal, which will be described later, is constant. 30 is a tuning circuit that takes out only the f ₂ signal, and 31 is a gate circuit that takes out only the f ₂ signal to be reproduced by the B head. The extraction of the _f2 signal is controlled by a head switching signal supplied from terminal 32. The output of the gate circuit 31 is
input to the AGC circuit 29 and its gate circuit 31
Change the amplification factor so that the output level remains constant. Note that the AGC circuit 29 has a peak hold type.
If an AGC circuit is used, the AGC works to maintain the maximum output level of the gate circuit 31 at a constant level. 33 is a tuning circuit that extracts only the _f1 signal, and 34 is a detection rectifier circuit. A signal indicating the track curvature corrected for the reproduction sensitivity of the head is outputted to the terminal 35 and supplied to the oscilloscope.
Note that the display used in the present invention may be a display other than an oscilloscope. The above is an embodiment of the present invention, but the present invention can be applied not only to VTRs having a control system that does not use control signals, but also to displaying track curvature of VTRs that use control signals. It should be obvious. At this time, it is possible to newly record one or two types of pilot signals. Effects of the Invention As described above, according to the present invention, it is possible to display the curvature of a recorded track almost in real time. As a result, when adjusting track bends during VTR manufacturing, work efficiency is improved because the bends can be seen directly, and there is no need to turn the track shifter, which has the effect of reducing work hours. Furthermore, it has a control system that does not use control signals.
It also has the effect of making it possible to adjust the track bending of a VTR.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the recording track and the scanning position of the head, Fig. 2 is a diagram showing the reproduction level of the luminance signal obtained when reproducing scanning is performed at the head position shown in Fig. 1, and Fig. 3 is a diagram showing the relationship between the recording track and the scanning position of the head. Figure 4 shows the _f1 reproduction signal level waveform obtained when scanning the magnetization locus in Figure 3. Figure 5 shows the signal shown in Figure 4 on an oscilloscope. FIG. 6 is a block circuit diagram showing an embodiment of the present invention;
FIG. 7 is a block circuit diagram showing another embodiment of the present invention, FIG. 8 is a diagram showing the relationship between variations in various heads and recording tracks, and FIG. Diagram showing the signal of f ₁ , 10th
11 is a diagram showing a head with high reproduction sensitivity and a track locus, FIG. 11 is a diagram showing reproduction signals of f ₁ and f ₂ when reproduced with the head shown in FIG. 10, and FIG. 12 is a diagram showing a further example of the present invention. FIG. 7 is a block circuit diagram showing another embodiment. 1...Head scanning direction, _A1 , _B1 ...Recording track, 2-4...Reproducing head, _f1 - _f4 ...Pilot signal, 6, 7...Signal indicating track curvature, 15... Sample hold circuit, 17...1
Frame delay circuit, 22... regular head, 23
...Head with a misaligned head height, 24...Wide head, 25...Head with high playback sensitivity, 2
9...AGC circuit.

Claims (1)

[Claims] 1. Magnetic recording and reproducing in which a magnetic tape is wound diagonally around a cylinder equipped with a rotating magnetic head, and information signals are recorded as a group of discontinuous recording tracks or information signals are reproduced from a group of discontinuous recording tracks. A device that displays the linearity of the scanning locus of the rotating magnetic head with respect to the magnetic tape of the device, the linearity of the scanning trajectory of the rotating magnetic head relative to the magnetic tape of the device being displayed every N tracks of the recording track group (N is an integer of 4 or more).
reproducing a magnetic tape on which a pilot signal is recorded, and extracting the first pilot signal that is reproduced when the rotating magnetic head scans tracks before and after the track on which the first pilot signal is recorded; A linearity display device for a magnetic recording and reproducing apparatus, characterized in that the level difference between the retrieved reproduction signals is displayed on a display in correspondence with the linearity. 2. The above method for a magnetic tape of a magnetic recording/reproducing apparatus which winds a magnetic tape diagonally around a cylinder equipped with a rotating magnetic head and records information signals as a group of discontinuous recording tracks or reproduces information signals from a group of discontinuous recording tracks. A device that displays the linearity of a scanning locus of a rotating magnetic head, the linearity of the scanning trajectory of a rotating magnetic head being displayed every N tracks of the recording track group (N is an integer of 4 or more).
A magnetic tape on which a pilot signal is recorded is reproduced, the reproduced pilot signal is passed through an AGC circuit, a second pilot signal recorded on a different track from the first pilot signal is reproduced, and the second pilot signal is recorded on a different track than the first pilot signal.
The AGC circuit is operated so that the reproduction level of the second pilot signal obtained when the rotating magnetic head scans the track on which the first pilot signal is recorded, and the rotating magnetic head the AGC of the first pilot signal that is reproduced when scanning tracks before and after the track on which the pilot signal is recorded;
1. A linearity display device for a magnetic recording and reproducing device, characterized in that a reproduction signal that has passed through a circuit is extracted, and a level difference between the extracted reproduction signals is displayed on a display in correspondence with the linearity.