1. Field of the Invention
This invention relates to a cassette for housing therein a record medium such as magnetic tape, video film, or a magnetic disc.
2. Description of the Prior Art
A number of different types of record media are now available in cassette form. A primary example is magnetic tape for use in audio or video tape recorders, although magnetic disc, video film and the like are also available in cassettes. The cassette is easily stored and handled for recording and/or reproduction, and effectively protects the magnetic tape within.
It frequently happens that an operator will wish to preserve a particular recording, and many cassettes provide a protection mechanism which can be activated to prevent accidental erasure or rerecording on the tape within the cassette. In one such conventional protection mechanism, a window opening in the surface of the cassette is formed with a protective tab or nail member overlaying the same. When the tab is broken off, a lever within the tape recorder may enter the window and inhibit the recording or erasure of signals on the tape. For example, this may be achieved by having the lever either prevent a mechanical recording button from being depressed or inhibit the operation of an erasing and/or recording circuit.
Of course, the operator may then change his mind and desire to reuse the tape for a new recording. With the type of conventional cassette described above, the operator often covers the window with a piece of adhesive tape to thereby prevent the lever of the tape recorder from entering through the window, and so rerecording and erasure is again possible. A difficulty is that the adhesive tape must be changed frequently, since the lever is pressed against the adhesive tape with a predetermined biasing force which will weaken and ultimately break the adhesive tape. This raises the prospect of a second difficulty, which is that the adhesive tape may break during a recording operation, so that the lever would then enter the window and interrupt the recording. If the signal to be recorded is, for example, a special broadcast, and is not available for replay, this is a serious disadvantage.
A second type of magnetic tape cassette has been proposed in which the protective tab can be detached from and then reattached to the window as often as desired. When the operator wishes to prevent erasure or rerecording, he detaches the tab, and when he wishes to record, he attaches the tab back to the cassette. However, such tabs are quite small and are easily lost.
Therefore, a third type of magnetic tape cassette has been proposed which includes an accidental erasure protection mechanism which may be set and reset, and does not include removable pieces. An example of such cassette is disclosed in Japanese Utility Model Application No. 163086/1983, published Oct. 29, 1983. In this cassette, there are two passages formed through the cassette housing. A central cavity in each passage has two subcavities separated by a detent, and a position indicating member in the form of a ball is located within each cavity and may be moved within the passage from one subcavity to the other past the detent by pressure exerted on the ball by a slender prong inserted through apertures at the ends of the passage. The ball in each passage is prevented by the detent from being inadvertently moved from one subcavity to the other. The positions of the balls within the respective passages may be detected through a window in the housing. This permits the operator to confirm the present state of the cassette and to select a new state, if desired, and the balls also serve, when in a predetermined particular position, to prevent the lever of the tape recorder from effectively entering the housing. This accidental erasure mechanism may be set and reset, and the balls can not be lost.
However, the apertures in the housing must be relatively long and narrow, so that the prong used to move each ball from one subcavity to another must also be long and thin. This makes it impossible to use such common articles as ballpoint pens or mechanical pencils as the prong. If the depth of the apertures is reduced, the balls would have to be relatively large to occupy the height of the cassette. However, they would then occupy a considerable volume within the cassette, which is disadvantageous since the cassette housing is generally filled by the tape and the reels on which it is wound.