Protective mechanism for electronic apparatus
BACKGROUND OF THE INVENTION 
     It is common practice to provide a keyslot in various types of apparatus, the slot being shaped to receive a mounting screw or the like, by which the apparatus can be secured to a support surface. This type of mounting arrangement is used in data processing equipment; however, in such equipment, it is necessary to cover the keyslot if it is of such size that foreign matter might fall through the keyslot and damage the inner circuit elements. Such a covering is also desirable to prevent possibly dangerous substances from falling out of the equipment, and it also prevents an individual from inserting a screwdriver or the like into the equipment and possibly being injured by high voltage. In some types of equipment, a knock-out piece might be provided which would cover the keyslot until it was used; however, if the equipment was later removed from its mounting, there would be no easy way to re-cover the opening to protect the inner circuitry. 
     The present invention solves this problem simply and inexpensively. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one type of electronic apparatus which might use the invention; 
     FIG. 2 is a bottom view of a portion of the apparatus of FIG. 1; 
     FIG. 3 is a sectional view along the lines 3--3 in FIG. 2; and 
     FIG. 4 shows the apparatus of FIG. 3 and illustrates one mode of operation of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The principles of the invention are described with respect to apparatus 10 which might constitute a piece of data processing equipment including a housing 20 made up of a first portion 30 in which electronic circuitry 22 might be mounted and a cover or base 40 therefor. The base or cover is provided with a keyslot 50, by means of which the apparatus 10 can be coupled to a mounting screw, as is well known in the art. 
     According to the invention, in order to block the keyslot 50 and prepare it for the desired usage, a sheet 60 of insulating material such as fish paper is placed over the opening on the inner surface 62 of the base. The sheet 60 is large enough to cover an area surrounding the keyslot. A thin sheet 70 of a relatively rigid material, for example, aluminum foil, is placed over the insulating sheet 60 and is cemented to the inner surface of the housing base. The sheet of metal foil 70 is larger in area than the insulating sheet 60, and its entire surface which extends beyond the insulating sheet is secured by a cement 74 to the base. A narrow strip along one edge 90 of sheet 70, which lies along the edge 100 of the base, is not cemented to the base to permit some movement of the sheets 60 and 70 when a screw is inserted in the keyslot. 
     In operation of the invention, when it is desired to mount the apparatus 10 on a mounting screw 110 (FIG. 4), it is pressed against the screw, and the screw forces the insulating sheet and the metal sheet slightly away from the inner surface of the base of the housing just enough to permit the screw to be set in place in the keyslot. This slight elevation of the cover sheets is permitted because edge 90 is not cemented to the cover plate. Later, if it is desired to demount the apparatus 10 by disengaging it from the screw, the metal strip 70 forces the insulating paper back down over the keyslot and again protects the interior of the equipment. 
     In addition to the advantages that can be readily seen from the above description of the invention, it is noted that the combination of foil and the paper hold the mounting screw tightly in place, and this arrangement would serve to prevent vibrations.