Lock for video tape cassette
FIELD OF THE INVENTION 
     The present invention relates to a lock for a video tape cassette, particularly to an improvement of the lock used in opening and closing the cap of the video tape cassette. 
     BACKGROUND OF THE INVENTION 
     The conventional lock for a video tape cassette has a complicated constitution as shown in FIG. 5. A base plate 4 is provided with a lock-releasing button 1 and a locking protrusion 1&#39;, which are inserted into a hole 2&#39; formed in the side wall 2 of the cassette and into a locking hole 3&#39; formed in the inner face of a cap 3 respectively. The base plate 4 is also provided with two shafts 5 which are respectively inserted into shaft holes 6 formed in the side wall. Further, there is installed a separate torsion spring 7 at one of the shafts 5 in order to provide elastic movements to the base plate 4. The use of such a separate torsion spring 7 necessitates the provision of spring protection ribs 9, 9&#39;. Thus, the construction of the conventional lock mechanism is very complicated, and the expense incurred for procuring and assembling the separate steel torsion spring significantly increases the total cost of the cassette. 
     SUMMARY OF THE INVENTION 
     In order to overcome the above-described disadvantages, the present invention provides a spring pole integrally formed with a base plate. This eliminates the need for a separate steel torsion spring. Further, because of the elimination of the separate torsion spring, the related portions within the cassette are simplified. For example, the ribs for accommodation of the separate torsion spring are not required. Further manual assembly is made simpler, and assembly by robots is also made possible. Therefore, a cheap and good quality video tape cassette can be manufactured through the use of the device of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a video tape cassette; 
     FIG. 2 is a cross sectional view of the assembled lock of the present invention taken along the line 2--2; 
     FIG. 3 is a cross sectional view of the assembled lock taken along the line 3--3; 
     FIG. 4 is a perspective view of the lock of the present invention; and 
     FIG. 5 is a cross sectional view of the conventional lock. 
     FIG. 6 is an exploded perspective view of a lower half member of the video cassette of FIG. 1 showing insertion of the lock of FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The above-described advantages of the present invention will become more apparent by describing in more detail the preferred embodiment of the present invention with reference to the attached drawings. 
     A base plate 15 is provided with a release button 11 and locking protrusion 12. The base plate 15 is further provided with supporting shafts 13 at the opposite upper sides thereof in order to suspend the base plate 15 by mounting the shafts 13 into shaft-receiving slots 14 which are formed on the side walls. At the upper side of the base plate 15 and aligned with the axis of the supporting shafts 13, there is provided a spring pole 16 (an upstanding rod spring). The end portion of the spring pole 16 is rectangularly bent forming an abutment portion 18 which is to be abutted with the ceiling of the upper half member 17. 
     According the device of the present invention, the spring pole 16 and the abutment portion 18 are integrally formed with the base plate 15, eliminating the need for using a separate torsion spring and thereby making the construction of the lock simpler. There fore, not only is manufacturing easier, but also assembly is extremely simpler, as will be described herein below. Minimal arrangement is needed, and all other formations which accompany the torsion spring in the conventional cassette are eliminated, thereby achieving a simpler locking mechanism. 
     The assembly process requires mounting the supporting shafts 13 into the shaft-receiving slots 14 formed in the side walls of the lower half member 17&#39;, (see FIG. 6), and then shutting down the upper half member. This shortens the assembly time in the case of manual assembly, and enables assembly by robots. The upper face of the abutment portion 18 is abutted onto the ceiling of the upper half member 17 of the cassette, while the tip face of the abutment portion 18 is contacted onto the side wall of the upper half member 17, ultimately yielding the same result that would arise if the tip of the spring pole 16 were secured onto the upper half member 17. As the spring pole 16 is aligned with the axis of the supporting shafts 13, the spring pole 16 will serve as an efficient spring. If the upper half member 17 is detached from the lower half member 17&#39;, the abutment portion 18 is also detached from the upper half member 17, and the spring pole 16 becomes disengaged. 
     To see the actuation of the lock in the process of assembly, the locking protrusion 12 is pushed inwardly by the closing movement of the cassette cap, and accordingly, the base plate 15 is pushed back pivotally around the supporting shafts 13. By the movement of the base plate 15, the spring pole 16 is bent to accumulate an elastic reactional potential. When the cassette cap is completely closed, the locking protrusion 12 is received into the locking hole formed on the cassette cap due to the reactional force of the bent spring pole 16, and the locking protrusion 12 is retained there due to the elastic strength of the spring pole 16. Thus the locked state of the cassette cap is formed. On the other hand, if the release button is pressed externally to the cassette against the elastic force of the spring pole 16, the locking protrusion 12 is taken out from the locking hole, which allows the cassette cap to open in a pivotal movement. 
     As described above, the device of the present invention simply comprises a base plate with a spring pole, a release button and a locking protrusion integrally formed on it. Thereby, the related interior structure of the cassette is also simplified, resulting in that the manufacturing and assembly of the cassette is greatly simplified. The device of the present invention not only shortens the required time for manual assembly, but also enables assembly by robots. Therefore, the manufacturing cost for the cassette is significantly lowered, and cheap and good quality products can be mass-produced through the use of the device of the present invention. 
     It should be understood that some changes and modifications can be added without departing from the scope of the attached claim.