Dynamic magnetic information storage or retrieval – Manual input recording
Patent
1986-08-21
1989-02-28
Faber, Alan
Dynamic magnetic information storage or retrieval
Manual input recording
360 22, 360 361, 360 331, 358335, 358337, H04N 578
Patent
active
048090972
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetic recording and reproducing apparatus for recording and reproducing one field of a video signal with the signal divided into a plurality of tracks with the use of a plurality of rotation heads, and more particularly to a recording and reproducing system capable of improving the joining of the portions of video signals which appear on the television screen.
BACKGROUND ART
Conventionaly, in a helical scanning type magnetic recording and reproducing apparatus (hereinafter referred to as "VTR"), especially in a VTR for domestic use, a method for recording one field video signal in one track has been utilized. By way of attempting the miniaturization of the VTR, a system has been devised in which the number of rotations of the rotation drum on which heads are installed is made twice and the diameter of the rotation drum is reduced to a half on an assumption that the relative speed of the head and the magnetic tape is not changed, that is, the characteristics of recording and reproducing is not changed. In this system, one field video of the signal to be recorded is divided into two tracks, and accordingly there exist two signal junctions in a field. When one of the signal junctions is placed at the horizontal blanking period similarly as in the conventional one field-one track recording system, the other signal junction comes at the center of the screen. Accordingly, in order to realize this system it is necessary to obtain a good junction of video signals at the center of the screen, but this is not so simple as will be described below.
Now suppose that an upper half portion and a lower half portion of the screen are recorded and reproduced by two heads, respectively. When there is a difference in tape tension between at the time of recording and at the time of reproduction, there arises a time discontinuation in the head switching position, producing what is called skew. This will be described with reference to FIGS. 4(a)-4(e).
In FIG. 4(a), the reference numeral 2 designates a magnetic tape, the numerals 3a and 3b designate tracks recorded by the heads 1a and 1b, respectively. If the head 1b is positioned at the position B where the recording is conducted at the same time as at the position A when the head 1a comes to the head switching point A at the reproduction, the junction of the signals at the center of the screen is made in a proper manner. This situation is shown in FIG. 4(b). The reference character P in the drawing represents a signal junction on the screen. However, when the position B is deviated to the position B1 caused by the variation in the tape tension the signal between the position B and B1 will be dropped as shown in FIG. 4(c). Furthermore, when the position B is deviated to the position B2, the signal between the position B2 and B will be repeatedly reproduced as shown in FIG. 4(d). Herein, FIGS. 4(c) and 4(d) shows the amount of skew which is exaggerated for purposes of explanation. In an actual VTR the amount of skew is less than a horizontal scanning period, and when it is received by a television receiver for domestic use, it appears as a curve on the screen by an AFC circuit having an internal synchronization system as shown in FIG. 4(e). In any event, when a skew occurs, a signal junction at the center of the screen is visible and undesirable, when viewed.
However, it is quite difficult to eliminate skew in a helical scanning type VTR. This has been an obstacle in the development of a field division type VTR.
Recently, as a result of the increase in the integration and the decrease in the cost of integrated circuits as a result of advances in semiconductor technology, it has become possible to correct the skew or jitter by including a digital time axis correction circuit (this is implemented by a time axis variation detection circuit and a time axis variation correction circuit, and this is hereinafter referred to as "DTBC") with a VTR. For example, in a DTBC shown in Japanese Laid Open Patent Publication No. Sho. 58-12
REFERENCES:
patent: 3809805 (1974-05-01), Kasprzak
patent: 4330795 (1982-05-01), Foerster
patent: 4541020 (1985-09-01), Kimura
Fujii Toshifumi
Kikuchi Jun
Faber Alan
Mitsubishi Denki & Kabushiki Kaisha
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