Image:Magnetic video tape recorder diagram Us004809115-003.png
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FIG. 2 is a perspective view of the appearance of a typical VHS type tape cassette;
FIG. 3A is a top plan view diagrammatically showing the VTR mechanism of the embodiment of the present invention;
Referring to FIG. 2, a cassette 1 includes a pair of reels 3 and 4 between which a magnetic tape 2 is passed. The magnetic tape 2 has opposite terminal ends 5 connected to transparent leader taper portions 6, one of which is shown in FIG. 2. The cassette 1 has a safety lug 7 on its back side, and, in order to permanently store the contents which are recorded on the tape 2, the safety lug 7 may be snapped so as to prevent re-recording (re-erasing) in interlocking relationship with a safety switch which will be described later. The cassette 1 is transported by a cassette loading device, and then loaded in a predetermined position determined by a chassis 9 (the state shown in FIG. 3A).
The following is a description of the aforementioned elements and switches.
Referring specifically to FIGS. 3A, 3B and 3C, the magnetic tape 2 is drawn out of the cassette 1 by the cooperation between tape drawing members 10a and 10b provided on the chassis 9, and is in turn partially wrapped around a cylinder (rotary head drum) 11. The magnetic tape 2 in this state is fed through the cooperative rotation of a capstan 12 and a pinch roller 13 so that recording, reproduction or the like is effected. In the meantime and in synchronism with the aforesaid operation, a reel table 15 (or 14) is rotated under the drive of tape take-up means (not shown) provided on the chassis 9. A reel 4(3) engaged with the reel table 15 (14) is also rotated to wind therearound the magnetic tape 2 which is fed in the aforementioned manner. Also, a reel 3(4) on a tape supply side causes motion of the thus-fed magnetic tape 2 and hence the associated reel table 14 (15). The respective reel tables 14 and 15 are secured to spindles 16 and 17 disposed upright and protrusively on the chassis 9 for rotation in cooperation with the spindles 16 and 17. The respective reel tables 14 and 15 have at their lower portions permanent magnets 14a and 15a each having circumferentially equally spaced magnetic forces. Rotation detecting elements (Hall elements) 18 and 19 are respectively disposed in the vicinity of the permanent magnets 14a and 15a for periodically detecting the aforesaid magnetic forces, thereby detecting the rotations of the reels 3 and 4, that is, the feeding of the magnetic tape 2. The result of the thus-detected reel rotation is transmitted to the body of the apparatus in which it is utilized for the purposes of providing a counter indication and an indication of the amount of tape remaining to be played, or in the form of protective functions used at the time of occurrence of troubles (for example, if no rotation is detected over a predetermined period of time in a tape playing mode, the tape playing mode is cancelled and then a tape stop mode is selected).
Also, the cassette 1 has an opening through which the light-emitting element 20 is inserted, and light rays 22a and 22b emitted from the light-emitting element 20 pass through holes 1a and 1b on opposite sides of the cassette 1, and then detected by the light-receiving elements 21a and 21b, respectively.
Referring to FIG. 3A showing the wound-up state of the magnetic tape 2, the light ray 22a emitted from the light-emitting element 20 passes through the transparent leader tape portion 6, and is then detected by the light-receiving element 21a. In this case, since the light ray 22b directed to the light-receiving element 21b on the take-up side is blocked by the magnetic tape 2, the element 21b does not detect the light ray 22b. Signals representative of the states of detection assumed by both elements 21a and 21b are transmitted to the body of the apparatus, in which it is judged that tape winding is completed, and thus the apparatus assumes an auto-stop or auto-rewind state. In the state of fast-forward or fast-rewind (not shown) as well, the same operation as described above is effected so as to prevent an excessive force from acting upon the magnetic tape 2. In addition, the aforesaid operation is also utilized for the purpose of judging whether or not the cassette 1 is held in position.
The aforesaid safety switch 23 is disposed in face-to-face relationship with the safety lug 7 disposed on the cassette 1. If the safety lug 1 is present, the switch 23 is pressed by the safety lug 1 and the switch 23 is depressed to turn on the associated contacts. The thus-generated signal is transmitted to the body of the apparatus and thus recording is enabled. If the safety lug 1 has been snapped, that is, the safety lug 1 is absent, the contacts are maintained in an OFF state and thus recording (erasing) is made unable.
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