The present invention relates to a casing for a magnetic tape cassette, and more particularly to a casing for a magnetic tape cassette which is conveniently used to record a digital signal such as, for example, a PCM signal.
A PCM recording and reproducing apparatus which is adapted to convert an analog signal, such as an acoustic signal or the like, into a digital signal such as, for example, a PCM signal, and in record the digital signal on a magnetic tape element for producing the same has recently been proposed. One example of such conventional PCM recording and reproducing apparatus, is typically constructed to use a rotary head for carrying out recording on a magnetic tape element at a relatively high density. More particularly, the recording and reproducing apparatus is adapted to draw out the magnetic tape element from a casing and wind it up on a rotating drum which is provided with the rotary head during its recording or reproducing operation.
A magnetic tape cassette used in such a PCM recording and reproducing apparatus is likely to cause a drop out to occur in a reproducing signal when a fingerprint, dust or the like adhere to a magnetic tape element. In order to avoid such a problem, it is necessary to keep the magnetic tape element in a casing as much as possible to protect the same. Also, in order to assure smooth drawing-out of the tape element from the casing during recording or reproducing, it is necessary to provide the casing with a space through which guide means of the apparatus are permitted to be inserted into the cassette casing.
In order to meet such requirements, a casing for a magnetic cassette was proposed which is typically constructed in such a manner as illustrated in FIGS. 1 to 4. More particularly, the casing includes a casing body 100 comprising an upper casing member (not illustrated) and a lower casing member 102 joined together to define a space therein for housing a magnetic tape element therewithin. The casing also includes a slider 104 slidably mounted on the lower casing member 102 so as to be slidable in a longitudinal direction of the casing body 100. The slider 104 is formed into a shape and a size sufficient to cover a bottom and a part of each of both lateral sides of the lower casing member 102. The casing is provided at a front portion thereof, with an opening which is selectively closed by a front cover (not illustrated). The front cover is pivotally mounted at the front portion of the casing body so that the cover may be actuated due to sliding movement of the slider 104 to selectively cover the front opening of the casing.
When the casing constructed as described above in which a magnetic tape element has been arranged therein to form a magnetic tape cassette, is inserted into a recording and reproducing apparatus, the slider 104 is moved in a rearward direction of the casing from a forward or foremost position illustrated in FIG. 1 to a rearward or rearmost position illustrated in FIG. 2, to pivotally move the front cover to expose the front opening of the casing, so that the magnetic tape element may be exposed through the front opening of the casing. During non-use of the magnetic tape cassette, the slider 104 is positioned at the forward position illustrated in FIG. 1, to close the front opening of the casing together with the front cover to sealingly maintain the magnetic tape element within the casing body.
In the conventional casing constructed as described above, and as illustrated in FIGS. 1 to 4, a torsion spring 106 is used which is supported, at a coil-like portion thereof, on a support boss 108 mounted on the lower casing member 102. The torsion spring 106 is engaged at one end thereof with the slider 104 through a stopper 110 and securely held at the other end thereof in a groove 112 formed on the boss 108.
The boss 108 for supporting the coil-like portion of the torsion spring 106, is formed into a thin shape in order to prevent formation of a sink mark thereon during injection molding. Accordingly, formation of the groove-like engagement 112 at the boss 108 causes a wall thickness of the boss 108 to be substantially decreased. Also, the end of the torsion spring 106 must be formed to have a length reduced to a sufficient degree to cause great force to be exerted on the boss 108, due to configuration of the support boss. Accordingly, when the boss is exposed to such a high temperature as encountered in a recording and reproducing apparatus under such conditions, the groove 112 of the boss 108 is subjected to such deformation as indicated by the chain lines in FIGS. 3 and 4. This causes a stroke of the torsion spring 106 to vary to a degree such that the force applied from the torsion spring to the slider 104 is significantly varied, thereby adversely affecting actuation of the slider.
Accordingly, it would be highly desirable to develop a casing for a magnetic tape cassette which is capable of continuously accomplishing stable actuation of a slider, with high reliability and for a long period of time, even under conditions of high temperature.