JPS6214320A - Tracking controller - Google Patents

Abstract

PURPOSE:To keep a reproduction signal at its maximum level by using a tracking control means which detects the change of signal level of a reproduction head under control and produces a tracking control signal in response to the state of said level change. CONSTITUTION:When an image head is set at a position (a), the reproduction signals S are decreased on a track #1 with displacement of the image head in the direction (c) and then increased with displacement of the head in the direction (b) respectively. While on a track #2 the signals S are decreased and increased with displacement of the image head in the directions (b) and (c) respectively. When the results of tracks #N and #(N+1) are inverted with each other, it is decided that the image head is set at the center point (a) of a image track. Thus the control signal e2 is not replaced at the restart point of a track #3. As a result, the signal e2 is kept at the fixed value when the image head is kept on a track and the signal S is kept at the maximum level with a stable fixed amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a helical scan type magnetic tape reproducing system.
In particular, the position of the magnetic head is adjusted to 1.1 so that the scanning locus of the magnetic head coincides with the track recorded on the magnetic tape by the rotating magnetic head. II In regards to an automatic tracking control device.

Conventional technology A method of aligning the scanning locus of the video playback head to the center of the video track is to ensure that the signal played back by the video playback head (generally a high frequency signal FM modulated by Video No. 48) is at its maximum. J. There is a way to control sea urchins. FIG. 2 shows the relationship between the relative fo M of the video playback head in the vertical direction with respect to the video track and the playback signal level.

When the video playback head is in the center of the video track (second
At point a) in the figure, the playback signal level reaches its maximum, and the video is replayed! [As the head moves away from the center of the video track (between a and b or between a and c in Figure 2), the playback signal level gradually decreases, and the video playback head moves away from the center of the video track to the video track width (also known as the girt band). tI: The signal level becomes minimum when the signal level is shifted by 1/2 distance (including 2nd point B or 6th point). 1-, the reproduction signal level is increased by 1 again.

Now, the video playback head is pointing to the video track as shown in Figure 2.
If it is at the point, the reproduced signal level SO is obtained. When the video reproduction head 11 is intentionally moved to point P1, which is closer to point b by ΔP, the reproduction signal level changes from SO to S.
decreases to l. On the other hand, the video image is changed from 80 points to 12 points.
When moving to the point, the reproduction signal level increases from SO to S2. Furthermore, when the video playback head is at point a, i.e. when racking is achieved, if the position of the video playback head is moved by a minute amount, the level of the playback signal will decrease regardless of the direction of movement; When the video playback head is completely off the video track as shown in the dot, if the video playback head is moved by a minute amount, the playback signal will increase regardless of the direction of movement.

When you move the video playback head by a minute amount, the direction of movement and
The center of the video track can be determined from the increase/decrease in the playback signal level, but from the IC point shown in Figure 2, this ll1
When starting IIIl, it may not be possible to know the center point a of images 1 to 3. This is because the playback signal level increases no matter which side the video playback head moves in the 11 vertical directions of the video track. If you think about it more broadly, you can definitely tell where the center of the video track is.

Next, the tracking operation n in the prior art will be explained with reference to FIGS. 2 and 6. I, II signal 1 signal e in Figure 6
1. e2. The relationship between the amplitude direction of e 3 and the head movement direction is such that the Lh direction in Figure 6 corresponds to the direction C in Figure 2, and the downward direction in Figure 6 corresponds to the lj direction in Figure 2 b. do. Further, in FIG. 6, it is assumed that the time flow changes from track #1 to track #3.

First, assume that track #1 is in an A-track state (point a in FIG. 2) in which the video head is completely on top of the video track. First, the video head is displaced by a small stone in the direction of C by 1IIIllllin number e1, and as a result, the reproduced signal S
decreases. Next, the control signal e1 causes the image head to
The small part is displaced in the direction of , and as a result, the reproduced signal @S increases. With the above operation, when the video head is displaced in the direction b, the reproduction signal S increases, so it is determined that the center of the video track is in the direction b from the current position of the video head, and the next track #2 At the start point of reproduction, a voltage is generated in the control signal e2 such that the video head is displaced in the direction b. As a result, in track #2, the video head position is at the second position.
Move to a' in the figure.

Track #2 also performs the same operation as track #1.

That is, the video head is moved from point a' to C by the v control signal e1.
When the head is displaced in the direction b, the reproduced signal S increases, and when it is then displaced in the direction b, the reproduced signal S decreases. Therefore, it is determined that the center of the video track is in the direction C from the current position of the video head, Control signal e at the playback start point of the next track #3
2, a voltage is generated that causes the image head to be displaced in the direction C. As a result, in track #3, the position of rad in the video is moved to a in FIG. 2 by IJI-4.

From track #3 onwards, this 2r operation is repeated, and the position of the video head is near the center of the video track (a in this example).
-a'), and the amplitude of the signal S is not constant and constantly fluctuates. In addition, e3 is e1+e2, and actually drives the head! IJ lj signal waveforms are shown.

As explained above, even if the control signal 01 of the prior art is used to displace the video head by a minute amount and determine the increase or decrease of the playback signal S, the result is no result! $! Since the position of the II-controlled video head is not fixed at the center of the video track but vibrates near the center,
The amplitude of the reproduced signal S will always fluctuate. When this reproduction signal S is tuned to II, analog VTRs experience S/N fluctuations and deterioration, DG (differential gain) and OP (differential phase) fluctuations, and digital VTRs also suffer from fluctuations and deterioration of the RA rate. This results in significant deterioration of the reproduced video signal.

The present invention has been made in order to eliminate the drawbacks of the conventional ones described above, and its purpose is to stably position the re-11 head in the center of the recording track.
- The purpose is to provide a tracking system that keeps the signal constant at maximum.

Lou shellfish! Tracking t, II control device according to the present invention is a tracking 1.11111 in an edge scan type magnetic tape reproducing device that performs tracking while slightly displacing a reproducing head in a direction substantially orthogonal to a recording track.
One device generates a pulse-like signal whose amplitude is protruding in a predetermined direction, and a pulse-like signal whose amplitude protrudes in a direction opposite to the predetermined direction, alternating with each other at a period approximately an integral multiple of one recording track period. At the very least, based on this pulse-like signal, the front reproducing head is displaced in a direction substantially orthogonal to the second recording track, and the signal level of the reproducing head under control by this & control means is changed. The present invention is characterized in that it includes tracking mi control means for detecting and generating i and lI sub-signals for tracking in accordance with the mode of this level change.

K11 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a plotter diagram showing the configuration of an embodiment of the present invention. In FIG. 1, a reproduced signal 1 reproduced from a magnetic tape 1 via a video head 2 is amplified by an amplifier 3 and rectified by a detector 4, and the output of the detector 4 is an envelope of the reproduced video signal a. It is output as a line (hereinafter referred to as reproduced signal A). The re-applied signal is further passed through a low-pass filter 5 to remove unnecessary ^-range frequency components, converted into a digital signal by an analogue digital converter 6, and then connected to a pass line 8 via an interface circuit 7. be done.

On the other hand, the playback head drive signal is passed through the pass line 8 through the interface circuit 12, converted into an analog signal by an 8-bit digital-to-analog converter 13, and is further amplified by the playback head drive signal amplifier 14 to drive the playback head. v
Manually transferred to JllI115. Video playback head 2 is a playback head drive! Since it is mechanically coupled to the I1 mechanism 15, the relative position with respect to the video track recorded on the tape 1 can be controlled by this reproducing head drive signal C.

A random access memory 9 (hereinafter referred to as RAM) for storing the A/D-converted reproduced signal j3A, a central processing unit (CPU) 10 for controlling this device, and a read memory in which a control program is stored. Only memories 11 are connected to the pass lines 8, respectively.

Next, the operation of one embodiment of the present invention will be described with reference to FIGS. 2, 3, and 4. In this embodiment, the control signal e
1 is such that the direction of displacement of the amplitude (that is, the direction in which the pulse amplitude protrudes) is reversed for each video track. Figures 3 and 4
Regarding the relationship between the amplitude direction of the control signals el, e2, and e3 in the figure and the head movement direction, the upper direction corresponds to the direction C in FIG. 2, and the lower direction corresponds to the direction b in FIG. 2, respectively. Also, Figures 3 and 4
In the figure, it is assumed that the flow of time changes from left to right, from track #1 to track #4.

First, with reference to FIG. 3, the manner in which the image head asymptotically approaches the center of the image rack will be explained. Assume that in track #1, the video head is located at a PO point that is off the center point a of the video track.

When the video head is slightly displaced in the direction C by the control signal e1, the reproduction signal S increases. Next, when the video head is displaced in the direction b by the $111111 signal e1, the reproduced signal S decreases. Track #2 again! At the start point of track #1, the same operation as track #1 is performed without changing the control signal e2. That is, when the video head is displaced in the direction b based on the control signal 01, the reproduction signal S decreases, and when the video head is displaced in the direction C, the reproduction signal S increases again.

When the video head is displaced in the direction C in tracks #1 and #2, the reproduction signal S increases, so at the start point of track #3, the 1110 signal e2 has a voltage that causes the video head to be displaced in the direction C. Occur. As a result, in track #3, the position of the image head moves to point 82 in FIG. Similar results are obtained for rack #3 and track #4, and the playback of track #5 starts (in this case, the control signal e2 becomes a low voltage that further displaces the video head in the direction of the 0 point, and the video head a in the center of the video track
approach the point. These operations are repeated and the image head moves to a
Reach point Ill '5; track 4.

Next, the case where the video head is at point a will be explained with reference to FIG. If you move it in the direction of b, the reproduction signal @S will increase.

On the other hand, in track #2, when the video head is displaced in the direction l), the re-Q signal 8 decreases, and when it is displaced in the direction C, the reproduced signal S increases. Track #N like this
It is determined that the video head is located at point a in the center of the video track on the platform where the result of track #N+1 is reversed.
It, II Goshin Qe2 is not updated at the playback start point of track #3. When the video head is on track in this way, the control signal 02 becomes a constant value and the playback signal S
remains at the maximum value and has a stable constant amplitude.

Control signal e1. Llltllll signal e2. Control signal 03
Each software is stored in ROM11 (
Since it is generated from J, the present invention can be applied to a 1-inch type VT.
Each 1. when implemented in R. The If formation of the II-III signals will be described in detail with reference to FIG.

When the reference signal of 60H7, which is equal to the rotation period and phase of the rotary head, is input to the timer circuit 16, the CP
An interrupt pulse is output to U10, and interrupt routine 1 is activated. 1, 11 In routine 1, frame pulses are read via input ports 1 to 17, and when O is reached, the count [1-counter (to be described later) is reset to O, and the process is completed. Timer 16t and frame pulse period 1f
Approximately 1.04 m5 divided into 32 equal parts of 33.4 mS, which is l'c.
OI on cycle 2+1) Outputs interrupt pulse 2 to Ll 10 and starts interrupt routine 2.

In the interrupt routine 2, the 21-r'l-7 counter defined in the RAM area is incremented by 1 each time the interrupt occurs, and the result is 2011(1).
(represents a hexadecimal number), OHelihira 1 is changed to -12=, and a 32-decimal counter that takes a value from O to I F +-1 is updated. Further, each processing program corresponding to the value of the control counter is executed and the processing is ended. When the value of the control counter is AI and 18 [10 o'clock, the video head is displaced in the direction of point 0 in Figure 2]! Program 1 is executed to displace the video head in the direction of point b in FIG. 2 when the control counter values are C+-+ and ICH.

Here, 11/A is connected via the interface circuit 12.
The data sent to the converter 13 will be explained. l')
The /A converter 13 is a circuit that converts the digital signal from 8 pins to an analog signal. -ta is 80H
When the image head is at point a in Figure 2, when it is 20H, the image head is at the second point.
Analog voltages located at point b in the figure and at point 0 in FIG. 2 when E OI-1 are output are output. The control signal e3 is an 8-bit signal obtained by adding the control signal e1 do mil + Oningo e2, and takes a chain from 2011 to EOH.
It has a 1-byte D/A output buffer defined in the RAM area.

The value of this D/A tll h buffer is sent to the D/A converter 13 via the interface circuit 12 to displace the video head.

Next, Program 1 and Program 2 will be explained.

In both programs, the displacement of the video head is equivalent to approximately 0.5 dB in amplitude change of the reproduced signal S, and when the control signal e3 and the video track have the relationship described above, the value of the control signal e3 is set to OA Ll. Ru. Therefore, in program 1, OAH is added to the value of r)/A output buffer, and in program 2, O△11 is subtracted from the value of 1)/A output buffer, and the component of control signal e1 is directly converted to is assigned to the value of

On the other hand, the control signal e2 is a signal 8 determined according to the change in the signal S before and after the video head is displaced by the If and II control signals 01 as described above, and is equal to 1 tot "1-/
When the counter is 1F1, the deception is performed and assigned to the υ control signal @e3.

In this embodiment, the polarization of the control signal e1 is inverted every period of one video 1 - rack, but the period of reversing the polarity is similar for other cycles such as 2 video 1 - rack circumference 1 or more. Increases the effect by 19. Also, the displacement amount of control signal 01 is
(Converted to yf◇ of Fi'l signal amplitude, 0.5 dll
I used a considerable amount of weight, but this change (Offl is also 0.5 dl)
It is not limited to the equivalent of l. In history, 1.11111 (No. 8 e1 is issued/1-U at a timing after a certain period of time has elapsed from the initial ill of the track, thereby simplifying the generation timing of this signal e1. However, the timing is not limited to always after a certain period of time has elapsed from the start of the track.

According to the present invention, as described above, the image head can be stably positioned at the center of the image rack, and the width of the signal can be stabilized at the maximum position. Therefore, Ana[1gVrR
Regardless of the digital VTR, the characteristics of the demodulated video signal or audio signal can maintain a stable snacking state.
It is especially effective for the recent J: Uni^ streetcar record-oriented narrow track outfits and tJ h replacements.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of an embodiment of the present invention, Figure 2 shows the width of the 11 signal with respect to the relative position of the image head and the rack, and Figure 3 shows the width of the signal. The video head of the invention is A]・Rack-=18 B, S υ control signal e
1. e2. Figure 4 for e3 1. L Control signals el and e2 when the video head of the present invention is on track
．． FIG. 5 is a timing chart explaining the operation of an embodiment of the present invention, and FIG. 6 is a diagram showing Gj in the prior art.
1 near the on-track. II Gobutsugo el, e2. e3
FIG. Explanation of symbols of main parts 1... Magnetic tape 2... Playback head 15... Playback head drive mechanism 16... Timer

Claims (1)

[Claims] A tracking control device for a helical scan type magnetic tape playback device that performs tracking while slightly displacing a playback head in a direction substantially perpendicular to a recording track, the tracking control device is configured to control a pulse-like signal whose amplitude is protruding in a predetermined direction and a pulse-like signal whose amplitude is protruding in a predetermined direction. pulse-like signals whose amplitudes protrude in the opposite direction to the above-mentioned direction are alternately generated at a period approximately an integer multiple of one recording track period, and based on these pulse-form signals, the reproducing head is moved approximately perpendicularly to the recording track. and a tracking control means that detects a change in the signal level of the reproducing head under the control state of the control means and generates a control signal for tracking according to the mode of the level change. A tracking control device characterized by: