JPS6321978B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking control method, and an object of the present invention is to provide a method for accurately detecting a track deviation from a track to be scanned by a rotary head during reproduction to perform tracking control.

In a helical scan type rotary head magnetic recording/reproducing device (hereinafter referred to as a VTR), there are variations in the tape guide groove formed on the fixed drum, variations in the inclination and height of the ball in the tape running system, and even the installation location of the fixed drum. Video track curvature inevitably occurs due to variations in the mechanism of the tape running system, such as variations in angle. Therefore, when recording
The best tracking condition cannot be obtained during compatible playback when playing back on a VTR different from the VTR. Particularly in home VTRs, where the tape running system has been simplified to reduce costs, it is extremely difficult to play back while ensuring the required high tracking accuracy as the recording and playback density increases.
Also, the VTR that recorded and the VTR that played back
In some cases, the distance from the position where the rotating head starts contacting the magnetic tape to the control head may be different, and in this case as well, the best tracking condition cannot be obtained and the S/N ratio of the reproduced signal deteriorates. Conventionally, normal tracking was performed by adjusting the tracking knob and delaying the playback control signal by the required time, but this was a control that moved the head scanning locus parallel to the longitudinal direction of one recording track. However, it was impossible to control the scanning so that it accurately followed 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 (direction of track width). be. Conventionally, the method of detecting track deviation during this tracking control involves recording pilot signals with different frequencies superimposed on the main information signal, and reproducing the tracks separately from the tracks on both sides of the track to be scanned during reproduction.
There was a method of detecting the track deviation direction and track deviation amount from the relative level difference between different types of pilot signals, but this method did not cause beat interference or limit the band of the main information signal to be recorded and reproduced. I didn't like it very much.

On the other hand, a dither (wobbling) method has conventionally existed as a method for detecting track deviation without recording a pilot signal on a recording track. In this method, the rotary head is displaced upward in the track width direction using a sine wave with a short frequency synchronized with the rotary drum, and as shown in FIG. Draw a sinusoidal scanning locus as shown by
By detecting the difference in FM playback signal level,
It was designed to detect track deviation.

However, in this conventional dither method, in order to detect one track deviation, a point where the rotary head is shifted upward and a point where the rotating head is shifted downward are required. However, since the upper and lower detection points are the upper and lower peak points of the sinusoidal scanning trajectories 2a and 2b, there is a drawback that errors occur in track deviation detection due to locational differences. In addition, when a magnetic tape is recorded using the azimuth recording method, when the rotating head is oscillated in the track width direction, time axis fluctuations occur in the reproduced signal, which appears as curvature or uneven color on the reproduced screen. There were flaws. Furthermore, as the dither frequency becomes higher, the amount of shift information increases, but at the same time, there is a drawback that the time axis fluctuation further increases. Furthermore, in the dither method, there is an inherent problem that even when optimal tracking is achieved, it is not optimal tracking in the true sense, so when the recording pattern is guard bandless azimuth recording, as the track width becomes narrower, the tracking distance from adjacent tracks increases. The disadvantage was that crosstalk became a problem.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIGS. 2 and below. This embodiment concerns a two-head helical scan system. FIG. 2 shows a block diagram of a tracking control system to which an embodiment of the present invention is applied. In the figure, numeral 3 denotes an input terminal, at which the frequency-modulated video signal is alternately transmitted, for example _, by two rotary heads having different azimuth angles.
A reproduced FM video signal obtained by reproducing a magnetic tape recorded by sequentially forming tracks shown in B ₁ , A ₂ , B ₂ . Here, in FIG. 3, one track records one field of FM video signal.

Reference numeral 4 denotes an input terminal in which a drum pulse synchronized with the rotation of the rotary head, for example, a symmetrical square wave having one period per rotation of the rotary drum as shown in FIG. 4A, is input. This drum pulse is input to a pulse generator 7, which generates a sampling pulse as shown in FIG. Here, as shown in FIG. 5, the sampling pulses are indicated by 1 to N, respectively, during the period when the rotating heads 17 and 18, which are disposed on the rotating drum 16 at positions facing each other at 180 degrees, are in contact with the magnetic tape. The pulse generator 7 outputs an output every time it passes a position.

On the other hand, the reproduced FM video signal that has entered the input terminal 3 is supplied to the envelope detector 5, where the envelope is detected and then supplied to the sample circuit 6.

The sampling circuit 6 samples the reproduced FM video signal level at N locations of one recording track using the sampling pulse from the pulse generator 7,
The signals are sequentially taken out and applied to the memory 9. Memory 9 stores this level.

On the other hand, the pulse generator 7 counts down the drum pulse by 1/2 to generate a head vibration signal with a period of 2 fields (1 frame) as shown in FIG. 4B. The signals are supplied to the head moving mechanism 15 through the drive amplifiers 14, respectively. Here, during the period (one frame) in which the head swing signal shown in FIG. During the period (one frame) in which the head swing signal is at a low level, the rotating heads 17, 1
8 is reproduced by the head moving mechanism 15 at a second height position lower than the reference height position.

Therefore, for example, when the rotary heads 17 and 18 are at their respective normal height positions (i.e., zero track deviation)
The rotary head 17 rotates the sixth field when reproducing the first field.
The rotary head 18 scans slightly above the recording track ₁ , as shown at _17a1 in FIG. and the next third
During field reproduction, the rotary head 17 scans slightly below the recording track 1, as shown by _17a3 in _FIG . Thereafter, the above operation is repeated. For convenience of illustration, one track is shown, but as explained in FIG. 3, each field is recorded on a different track.

On the other hand, when the rotary heads 17 and 18 are shifted upward, a scanning trajectory shown in FIG. 6B is drawn, and when they are shifted downward, a scanning trajectory shown in FIG. 6C is drawn. Here, in FIGS. 6B and 6C, 17b ₁ and 17c ₁ are the first field reproduction positions of the rotary head 17;
b ₃ and 17c ₃ are the third field playback positions of the rotary head 17, and 18b ₄ and 18c ₄ are the fourth field reproduction positions of the rotary head 18.
Indicates field playback position.

By the way, in a VTR, it is not possible to simultaneously obtain two scan trajectories, one above and one above, for a regular track.
Furthermore, in the case of a two-head VTR, it is not inconvenient to regard the bottom ten or so tracks played by heads of the same channel as exactly the same track.
Therefore, as mentioned above, the rotating head 1 is rotated in units of one frame.
By moving 7 and 18 up and down in the track width direction, tracking information covering one track of two heads can be obtained in a 4-field section, and the
There is no problem even if the direction of track deviation is detected by comparing the FM video signal levels.

A head control method based on these detection results will be explained. First, as shown in FIG. 7, if the data 20 at any i position from the sample circuit 6 is the FM playback signal level when the head is shifted upward, the system controller 8 instructs the switch _S1 to be turned on. 1a side, and data is input into the memory 9 in the order of the sample positions. For example, the data of the first field of the rotary head 17 is input to the left side of the memory 9 in FIG. 7, and the data of the second field of the rotary head 18 is input to the right side. Next, if the data 21 at the i position is the FM playback signal level when the head is shifted down, then
Switch S ₁ according to instructions from system controller 8
falls to the 1b side and is sequentially sent to the comparator 10. The comparator 10 first compares the data of the FM playback signal level when shifted upward from the memory 9 at an arbitrary i position with the FM playback signal level when shifted downward in the data comparison circuit 10-1, and calculates the FM playback signal level. The difference is output to the minute displacement output circuit 10-2.

Furthermore, the output of the data comparison circuit 10-1 is also input to the memory 19. The data input to the memory 19 is compared with the previous data stored in each position of each channel, and if the input data is larger, it is replaced with the previous data. In this way, the maximum value of each position of each channel, that is, the optimum tracking value is always input into the memory 19. On the other hand, the tracking control signal from the minute displacement circuit 10-2 is input to the memory 11. Auto-tracking control is repeated at a cycle of 4 fields using this tracking control signal.

Here, when the data obtained from the sample circuit 6 and the data at each position of each channel of the data in the memory 19 are compared in the data comparison circuit 10-1 and become the same, the system controller 8 switches the switches S ₂ , Open _S3 . Therefore, no new tracking control signal is input to the memory 11, and no dither pulse from the pulse generator 7 is input to the head moving drive amplifier 14. In this way, the head moving mechanism 1
Since only the tracking information signal corresponding to the maximum displacement level is input to head 5, heads 17 and 18
is the true optimal tracking state.

Furthermore, after the input of this dither pulse to the head moving drive amplifier 13 is stopped, the data comparison circuit 10-1 compares the data from the sample circuit 6 with the maximum value of each sample position of each channel in the memory 19. If the two are always the same, the optimum tracking state is maintained, but if the two differ by more than a certain value, the system controller 8 closes the switches S ₂ and S ₃ . Then, the head moving drive amplifier 1 is again connected to the pulse generator 7.
3, the heads 17 and 18 start dithering, and the data comparison circuit 10-1 performs the same data comparison as above with the aim of achieving an optimal tracking state, and outputs a tracking control signal to the memory 11. . In this way, true optimal tracking control is always possible.

As described above, the tracking control method according to the present invention applies a head swing signal to the head moving mechanism in a magnetic reproducing device to track M tracks in a direction perpendicular to the longitudinal direction of a recording track on a magnetic tape (however, In a tracking control method, a rotary head (M is a positive integer) is displaced at a 2M field period, a track deviation is detected based on the level of a reproduction signal of the rotary head, and tracking control is performed using the detected output. 1 field period when scanning is performed with a downward shift
The sample level of the FM playback signal at the above sample points is stored in the first memory, and the FM of one field period when the rotary head shifts downward or upward and performs scanning for each M field.
A comparator compares the sample level of the reproduced signal and the sample level at the same sample point among the sample levels before the M field from the first memory to detect tracking deviation, and determines the optimal tracking control amount at each sample point. After the output signal is obtained and stored in the second memory, the application of the head swing signal to the head moving mechanism is stopped, and the head moving mechanism is driven and controlled based on the output signal of the second memory. It is possible to eliminate screen distortion and color unevenness caused by time axis fluctuations during playback of azimuth-recorded magnetic tape, which is seen in this method, and since no pilot signal is recorded, it is possible to limit the recording and playback signal band and prevent bead interference. In addition, since the number of samples per track N does not depend on the frequency of the head vibration signal, the amount of information can be increased by the desired amount, and since this sample point is at the same location on each track. , it is possible to eliminate errors that occur in track deviation detection, and since tracking is always optimal, even if the recording pattern is guard bandless azimuth recording, there is no influence of crosstalk from adjacent tracks as the track width becomes narrower. There is an effect. Furthermore, after stopping the swinging movement of the head for detecting track deviation during optimal tracking, the sample level of the FM playback signal of each field and the optimal tracking value of the sample level from the third memory are determined at the same sample point. The sample level is compared with the optimum tracking value by a comparator, and when the two differ by more than a certain value, a head swing signal is applied to the head moving mechanism, and the sample level of the FM magnetic reproduction signal is stored in the first memory. Since the storage of the optimal tracking control amount in the second memory and the storage of the optimal tracking value of the sample level in the third memory are restarted, even if the trajectory of the rotary head deviates from the optimal tracking state, the tracking can be performed immediately. The effect is that the correction is performed and the optimal tracking state can be maintained at all times.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing track deviation detection using a dither method, Fig. 2 is a block diagram showing an embodiment of the auto-tracking method of the present invention, Fig. 3 is a recording pattern of a magnetic tape, and Fig. 4 is a diagram showing track deviation detection. Figure 5 is a diagram showing the pulses for detection, Figure 5 is a diagram showing the rotating drum, Figure 6 is a diagram showing the relative positional relationship between the rotating head and the track locus, and Figure 7 is a detailed diagram of the comparator and memory. be. 3...FM playback signal input terminal, 4...Drum pulse input terminal, 5...Envelope detector, 6...Sample circuit, 7...Pulse generator, 8...System controller, 9, 11, 19...Memory, 10...
Comparator, 12... Head control voltage generation circuit, 14...
Head moving drive amplifier, 15...Head moving mechanism.

Claims (1)

[Claims] 1. In a magnetic reproducing device, a head swing signal is applied to a head moving mechanism to move M heads in a direction perpendicular to the longitudinal direction of a recording track on a magnetic tape (M is a positive integer). In a tracking control method, a rotary head is displaced at a 2M field period, a track deviation is detected based on the level of a reproduction signal of the rotary head, and tracking control is performed based on the detected output. The sample level of the FM playback signal at one or more sample points in one field period when scanning is stored in a first memory, and the one rotary head shifts downward or upward and scans every M fields. of one field period when performing
A comparator compares the sample level of the FM playback signal and the sample level at the same sample point among the sample levels before the M field from the first memory to detect a tracking deviation, and performs optimal tracking at each sample point. After obtaining the control amount and storing it in the second memory, the application of the head swing signal to the head moving mechanism is stopped, and the head moving mechanism is driven and controlled based on the output signal of the second memory. A tracking control method characterized by: 2 Apply a head swing signal to the head moving mechanism in the magnetic reproducing device to move M (M is a positive integer) rotating heads in a 2M field in a direction perpendicular to the longitudinal direction of the recording track on the magnetic tape. In a tracking control method in which a rotary head is displaced periodically, a track deviation is detected by the reproduction signal level of the rotary head, and tracking is controlled based on the detection output, when one rotary head shifts upward or downward during scanning. When the sample level of the FM playback signal at one or more sample points during one field period is stored in the first memory, and the one rotary head shifts downward or upward for each M field and performs scanning. of one field period of
A comparator compares the sample level of the FM playback signal and the sample level at the same sample point among the sample levels before the M field from the first memory to detect a tracking deviation, and performs optimal tracking at each sample point. After obtaining the control amount and storing it in the second memory, and storing the optimal tracking value of the sample level of the FM playback signal at each sample point during optimal tracking in the third memory, the control amount is transferred to the head moving mechanism. The application of the head swing signal is stopped, and the head moving mechanism is driven and controlled based on the output signal of the second memory, and the sample level of the FM playback signal of each field and the sample level from the third memory are controlled. The comparator compares the optimum tracking value of the sample level of the same sample point with the optimum tracking value of the sample level of the optimum tracking value of the FM.
The storage of the sample level of the reproduced signal in the first memory, the storage of the optimal tracking control amount in the second memory, and the storage of the optimal tracking value of the sample level in the third memory are restarted. A tracking control method characterized by: