JPS6321966B2 - - 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 pole 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
There may be a difference in the distance from the position where the rotating head starts contacting the magnetic tape to the control head, and in this case too, the best tracking condition cannot be obtained and the SN ratio of the reproduced signal deteriorates.

Therefore, in the past, normal tracking was performed by adjusting the tracking knob and delaying the playback control signal by the required time, but this was done by moving the head scanning trajectory parallel to the longitudinal direction of one recording track. However, it was impossible to control the scanning so as to accurately follow the curve of a single track.

Therefore, in order to perform tracking control with higher precision, 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 direction of the track width). There is a need.

Conventionally, there have been two methods for detecting track deviations during tracking control, in which pilot signals with different frequencies are superimposed on the main information signal and recorded, and the tracks are reproduced 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 of the pilot signals, but this method caused beat disturbance and also limited the band of the main information signal to be recorded and reproduced. I didn't like it.

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 shown respectively in
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.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIGS. 2 and below. The present invention relates to 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, 3 is an input terminal, and the frequency-modulated video signal is input to two terminals having different azimuth angles.
In FIG. 3, A ₁ ,
A reproduced FM video signal obtained by reproducing a magnetic tape recorded by sequentially forming tracks shown as B ₁ , A ₂ , B ₂ . Here, in FIG. 3, one track records one field of FM video signal. 4 is an input terminal, which is synchronized with the rotation of the rotary head, for example, the fourth input terminal of one period per rotation of the rotary drum.
An incoming drum pulse is a symmetrical square wave as shown in Figure A. 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 on 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 converts the drum pulses by 1/1 during normal playback.
After counting down by 2, a head oscillation signal having a period of 4 fields (2 frames) is generated as shown in FIG. Here, during the period (one frame) when the head swing signal shown in FIG. 4B is at a high level, the rotating heads 17 and 18 are moved by the head moving mechanism 15.
During reproduction at a first height position higher than the reference height position, and during the period (one frame) in which the head swing signal is at a low level, the rotary heads 17 and 18 are moved to the reference height position by the head moving mechanism 15. is reproduced at a second height position lower than .

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, and 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, by moving the rotary heads 17 and 18 up and down in the track width direction in units of one frame as described above, tracking information covering one track of two heads is obtained in a four-field section, and the tracking information at that time is obtained.
There is no problem even if the direction of track deviation is detected by comparing the FM video signal levels.

In the control based on these detection results, first, each N number of FM video signals reproduced in the first and second fields by the rotary heads 17 and 18 shifted upward is stored in the memory 9 shown in FIG. sampling data is stored. Then, when playing the next 3rd and 4th fields, the rotary head 1
7 and 18 are shifted downward, and each N sampling data is stored in the memory 9 in the same manner as described above.

Next, in the voltage comparator 10, the sampling data of the third field is compared with the sampling data of the first field, and the sampling data of the fourth field is compared with the sampling data of the second field. The output signal of the voltage comparator 10 is stored in the memory 11 as a tracking deviation detection signal, and then supplied to the tracking signal generation circuit 12, where the rotation head 1
After being converted into a tracking signal for track deviation correction according to each scanning position of 7 and 18, the adder circuit 1
3, where the pulse generator 7
This signal is added to the head vibration signal shown in FIG. 4B. The output addition signal of the adder circuit 13 is sent to the drive amplifier 1.
4 to the head moving mechanism 15,
The head scanning locus is controlled so that it becomes as shown by the dashed line or dashed line in FIG. 6A. The above operations are performed under the control of the system controller 8.

In this way, according to this embodiment, the rotary head is vertically moved (oscillated) in the track width direction in units of one frame, and the reproduced signal when scanning is shifted upward is transmitted to the N on one recording track. Track deviation is detected by storing data obtained by sampling at N sampling points in memory and comparing this data with N sampling data of the reproduced signal when scanning with the head shifted downward. , it is possible to eliminate the curvature and color unevenness of the reproduced screen that occur when reproducing an azimuthally recorded magnetic tape as in the conventional dither system. Furthermore, even if the head is shifted up or down, the sample points are at the same location, so no track shift detection error occurs.

Next, consider control when the playback pattern differs for each frame. Figure 7 shows the video track and playback locus, and as you can see, in still, normal, 2x speed, and 3x speed playback,
The change in the envelope detection level of the reproduced signal is in one frame period in units of frames. FIG. 9A shows the envelope detection level for triple-speed playback, and FIG. 9B shows the envelope detection level for static and double-speed playback. In triple speed playback, it is actually one field period, but if the frame is taken as a unit, it can be said to be one frame period. Note that FIGS. 9D and 9F show drum pulses and sampling pulses, respectively. When the envelope detection level changes in one frame period as described above, the pulse generator 7 generates a head oscillation signal with two frame periods as shown in FIG. occurs.

In addition, during 2.5x speed playback, the envelope detection level of the playback signal changes at a 2-frame period as shown in Figure 9C, and during 1/2x speed playback, it changes at a 2-frame period as shown in Figure 9H. . At this time, the pulse generator 7 generates a head oscillation signal having a period of four frames as shown in FIG. 9G in response to instructions from the control signal.

In addition, during 1/3 speed playback, the envelope detection level of the reproduced signal changes at three frame periods as shown in FIG. Generates a head swing signal with a frame period.

In other words, the pulse generator 7 controls the change in the envelope detection level of the reproduced signal on a frame-by-frame basis according to the instruction of the control signal supplied from the terminal 20.
When it is a frame period, a head swing signal having a 2·I frame period is generated. At the same time, the system controller 8 receives 4, 1, and N frames for 2, I frames in accordance with the control signal supplied from the terminal 20
storage of sampling data in the memory 9,
Head swing signal is low level (or high level)
The voltage comparator 10 compares the sampling data of the I frame with the sampling data of the I frame in which the head vibration signal is at a high level (or low level), and the track deviation detection signal obtained here is stored in the memory 11. After that, the tracking signal is supplied to the tracking signal generation circuit 12.

As a result, the change in the envelope detection level is 2.5 times faster than that during normal playback of one frame period.
Even during special playback such as 1/3x speed playback, there is no error in track shift detection, and distortion and color unevenness on the playback screen can be eliminated in the same way as during normal playback.

As shown in FIG. 8, the head moving mechanism 15 uses a well-known bending bimorph consisting of piezoelectric ceramic plates that bend in different directions and are bonded together via a conductive flexible plate, and one end of the bimorph is fixed. A rotating head is attached to the free end of the other end, and depending on the polarity and value of the applied voltage, one of the piezoelectric ceramic plates expands and the other contracts, causing the rotating head to move in a direction perpendicular to the longitudinal direction of the track. It is possible to use a device designed to displace the . In addition, a total of two rotating heads are attached to each opposing tip of a rotating base body that rotates integrally with the rotating drum, and the rotating base body receives tracking control power using a fulcrum member that supports its center as a fulcrum. Depending on the situation, a seesaw operation may be used on a plane perpendicular to the rotating surface of the rotating drum.

As described above, the tracking control method according to the present invention applies a rectangular wave head swing signal to the head moving mechanism in a magnetic reproducing device to move the recording track two times perpendicularly to the longitudinal direction of the recording track on the magnetic tape.
In a tracking control method that displaces each rotary head, detects a tracking deviation based on the level of the reproduced signal of the rotary head, and performs tracking control based on the detected output, the envelope detection level of the FM reproduced signal of the rotary head is determined at an I-frame period. When changing, the head oscillation signal has a period of 2I frames, and the sample level of the FM playback signal at one or more sample points in the I frame period when one rotating head shifts upward or downward and performs scanning is calculated as The sample level of the FM playback signal during the I-frame period and the I-frame from the first memory when one rotary head shifts downward or upward for each I-frame and performs scanning. A comparator compares the previous sample level with the sample level at the same sample point, stores the track deviation detection signal output from the comparator in a second memory, and uses the track deviation detection signal read from the second memory. A tracking control signal is generated based on the tracking control signal, and a head swing signal is added to the tracking control signal to drive and control the head moving mechanism. Screen distortion and color unevenness caused by axis fluctuations can be removed, and since no pilot signal is recorded, there is no risk of limiting the recording/playback signal band or causing bead interference, and the number of samples per track N is Since it 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 for each track, errors that occur in track deviation detection can be eliminated. Furthermore, even if the tape speed is variable, the above-mentioned effects can be obtained which are the same as those obtained at normal speed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a head scanning locus according to the conventional method, Fig. 2 is a block system diagram showing a tracking control system to which an embodiment of the present invention is applied, and Fig. 3 is a diagram showing a magnetic tape using the azimuth recording method. 4A to 4C are signal waveform diagrams for explaining the operation of FIG. 2, and FIG. 6A to 6C are diagrams showing examples of head scanning trajectories according to the method of the present invention, FIG. 7 is a diagram illustrating video tracks and reproduction trajectories, FIG. 8 is a diagram illustrating a head moving mechanism, and FIG. 9 is a diagram illustrating reproduction. FIG. 3 is a diagram for explaining the relationship between the envelope detection level of a signal and a head vibration signal. 1... Recording track, 3... Playback FM video signal input terminal, 4... Drum pulse input terminal, 5... Envelope detector, 6... Sample circuit, 7... Pulse generator, 8... System controller, 9, 11... Memory, 12... Tracking signal generation circuit, 13... Adder, 14... Head mechanism drive amplifier, 15... Head moving mechanism, 16... Rotating drum, 17, 1
8...Rotating head.

Claims (1)

[Claims] 1 A magnetic reproducing device applies a rectangular wave head swing signal to the head moving mechanism to displace two rotary heads in a direction perpendicular to the longitudinal direction of the recording track on the magnetic tape, and performs reproduction of the rotary heads. In a tracking control method that detects a track deviation based on the signal level and performs tracking control based on the detection output, when the envelope detection level of the FM playback signal of the rotary head changes at an I-frame period, the head swing signal is changed to 2I frames. period,
The sample level of the FM playback signal at one or more sample points in the I frame period when scanning is performed with one rotating head shifted upward or downward.
The sample level of the FM playback signal during the I-frame period and the I-frame from the first memory when the first rotary head shifts downward or upward for each I-frame and performs scanning. A comparator compares the sample level of the same sample point among the previous sample levels, and stores the track deviation detection signal output from the comparator in a second memory;
generating a tracking control signal based on the track deviation detection signal read from the second memory;
A tracking control system characterized in that the head moving mechanism is driven and controlled by adding the head swing signal to the tracking control signal.