Abstract:
A system is provided for increasing the recording/play-back time for video tape devices. A tape is utilized on which signals are recorded in one direction for one half the tape width and in the opposite direction for the other half of the tape width. The tape drive mechanism automatically reverses at the end of feed in each direction and when the tape feed direction changes the relative vertical position of the tape head (or heads) with respect to the tape also changes.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to video tape recording and play-back and in particular to a system for increasing the recording/play-back time of video cassettes. 
     In video tape devices, as for example home recorders, for economic reasons, it is highly desirable to minimize the tape consumption rate. This is particularly so for the magnetic recording/play-back of color video signals. As a result, the tape advance speed has been reduced as much as is technically feasible and the magnetic surface of the tape is used extensively. 
     Such home video recorders are usually operated with tape cassettes. Accordingly, the dimensions of the cassette housing limit the available tape play time. It is desirable to keep the cassettes as compact as possible while maximizing the available play time of the tape cassette. Of the cassette dimensions, the cassette height (which is determined by the tape width) has little overall effect on the cassette compactness. Heretofore devices for the recording/play-back of slanted track video signals operated on tape cassettes in which the tape travelled operationally in one direction only and the tracks extended over substantially the entire top width. 
     In view of the above, it is the principle object of the present invention to provide a video tape recording/play-back system of the cassette type wherein the time capacity of the cassette is increased by substantially fifty percent without substantially changing the cassette dimensions and wherein the tape band width remains the same or is only slightly changed. 
     SUMMARY OF THE INVENTION 
     The above and other beneficial objects and advantages are attained in accordance with the present invention by providing a system wherein the tape cassette is fed first in one direction and then in the opposite direction. The direction of drive is automatically reversed at the end of travel in each direction. 
     The inclined track video signals are recorded/played-back on/from half the tape width for each direction of tape travel. Although the tape cassette could be turned over by hand after each direction of travel, such an arrangement would not permit automatic operation. Further, while mechanical turning devices may be feasible, such devices would increase the expense of the video recorder or play-back device and would require additional space. In view of this, the present invention further contemplates an arrangement whereby the head drum is shifted vertically (i.e., perpendicular to the direction of tape travel) with each reversal of the tape direction and is simultaneously rotated 180°. The sound head and erasure head are also shifted. Alternately, with each reversal of the tape direction the cassette support and tape spools may be shifted vertically. In both cases the vertical shifting is by an amount substantially equal to one half the tape width. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a simplified, fragmentary sectional view of the head drum of a device incorporating the present invention; 
     FIG. 2 is a top plan view of the device of FIG. 1; and, 
     FIG. 3a and FIG. 3b are schematic views of the winding of a tape feeding mechanism at the head drum. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is now made to the drawings and to FIG. 1 in particular wherein a video recorder head drum 1 for recording/play-back of inclined-track video signals is depicted along with a section of tape 2 and tape feed guide pins 3 and 4. To simplify and clarify the present description, the associated portions of the video recorder and cassette (i.e., cassette casing, capstan drive, head drum drive, audio-synchron head, erasure head, tape feed, tape spool drive, etc.) are not shown. 
     The head drum 1 is mounted on a chassis 5 and consists of two coaxial drum portions 7 and 8 each in the form of a hollow cylinder mounted on the common shaft 6. The lower cylinder 7 which is substantially stationary acts as a guide for the magnetic tape 2 and also serves as a bearing for shaft 6. The upper drum portion 8 is coupled to shaft 6 and is driven by the shaft. To this end, roller 9 is provided which is coupled through belt 10 with a drive motor (not shown). Video heads 12 and 13 are provided extending into slot 11 which is defined between the upper and lower drum portions 8 and 7. The video heads 12 and 13 are mounted below the rotating upper drum portion 8. 
     A tape feed support 14 for the magnetic tape 2 extends helically about the face of lower drum 7. The tape support may be coupled rigidly to the lower drum portion or may be vertically adjustable. A bearing neck 15 in the lower drum portion 16 serves to enable the head drum 1 to be plugged into guide jacket 16 which is provided in chassis 5. An adjustment cam 17 on the chassis cooperates with an adjustment lever 18 at the end of the bearing neck 15 to permit the lifting or lowering of head drum 1 and the simultaneous rotation of the lower drum portion 7 and thereby a vertical adjustment of the tape feeding means 14 during a circular movement of lever 18. 
     In accordance with the present invention, the recorded inclined track video signals extend along one half the width of magnetic tape 2 during each directional feed cycle. Thus, in FIG. 1 only the lower magnetic tape half 2a is recored or scanned as the tape feeds in a first direction. During the reverse movement of the tape the upper tape half 2b is recorded or scanned. To this end, the head drum 1 is lifted vertically by an amount equal to substantially one half the tape width and the tape feeding position is adjusted to the changed vertical position of the head drum by rotating the lower drum portion 180°. Simultaneously the audio or synchron track as well as the erasure head are adjusted vertically. To this end, the sound and erasure heads may be vertically adjustable or switchable between a plurality of heads located at the raised and lowered vertical positions. 
     Alternatively, a double head arrangement, electrically switchable, on the head drum may be utilized whereby the two separated video heads are offset from each other by one half the tape width. One example is shown in FIG. 1 wherein a second video head 19 (shown in phantom) is offset vertically from the first set of heads 12 or 13, by one half the tape width. Where a second head 19 is used, the need for mechanical vertical adjustment and pivoting is eliminated and replaced with switch means to select between the first set of heads 12 and 13 and the second head 19 upon reversal of the tape direction. Thus, when the tape moves in one direction the lower head 12 is activated (while head 19 is deactivated) and when the tape moves in the opposite direction head 19 is activated (and head 12 deactivated). The net result is that upon a reversal of the tape&#39;s direction the relative position of the active head with respect to the tape is shifted. 
     As a further alternative when the tape feed direction is changed the relative vertical position between the video head and tape may be adjusted by adjusting the tape rather than the head drum. This may be accomplished by adjusting the tape feed pins 3 and 4, feed support 14 and the cassette support (not shown) with each reversal of the tape direction. 
     In FIG. 2 the winding of magnetic tape 2 about the head drum 1 is shown. The video (and, if desired, sound and errasure) heads 12 and 13 are offset 180° with respect to each other. FIGS. 3a, and 3b depict the winding of the tape feeding means which extends about the face of the lower drum portion 7. The different vertical positions of the tape feeding means are shown. Thus, in accordance with FIG. 3a the lower half 2a of the magnetic tape is provided with a video signal on inclined tracks slanted so that they may be recorded or scanned as the tape moves in the direction of the arrow A and engages the tape feed support 14a. When the tape completes its travel in the direction A and is reversed, the head drum rotates 180° and the tape assumes the position in FIG. 3b. In the position of FIG. 3b the tape moves in the direction of the arrow B. The upper half 2b of the magnetic tape is provided with video signals tracks inclined to be recorded or scanned as the tape moves in the direction B and the tape is supported along surface 14b which is vertically offset from surface 14a by one half the tape width as shown in FIG. 3a. Simultaneously with the reversal of the tape direction the head drum is shifted vertically by one half the tape width. 
     Thus, in accordance with the above the aforementioned objectives are attained.