Abstract:
It is common for the prongs of an electrical plug at the end of an electrical cord to be left exposed when not plugged into an electrical receptacle. In the present invention, a locking cap is provided for mounting onto and locking onto the prongs for safety and security. The locking cap when in place deters use of the power tool or other electrical appliance to which the cord is attached, and covers and protects the protruding prongs from damage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to security devices. It is common for the prongs of an electrical plug at the end of an electrical cord to be left exposed when not plugged into an electrical receptacle. There is often nothing to deter an unauthorized user or untrained user, such as a child, from plugging the electrical cord&#39;s plug into an electrical receptacle and using the power tool or other electrical appliance to which the cord is attached. It is also common for the exposed prongs to become bent or even broken from being stepped on or from contact with other items in the course of storage or transit.  
         SUMMARY OF THE INVENTION  
         [0002]    A security cap is provided for mounting onto the prongs of an electrical plug for safety and protection of the prongs. The security cap when in place deters use of the power tool or other electrical appliance to which the electrical plug is attached, and covers and protects the protruding prongs from damage.  
           [0003]    The security cap for electrical plugs comprises:  
           [0004]    a) a lock body adapted to fit over electrical prongs that protrude from the end of an electrical plug;  
           [0005]    b) a prong retainer mounted in the lock body, the prong retainer adapted to retain a prong that protrudes from the end of an electrical plug until moved to a prong disengaging position;  
           [0006]    c) a release member mounted in the lock body and conditionally moveable against the prong retainer such that sufficient movement of the release member against the prong retainer causes the prong retainer to move to a prong disengaging position;  
           [0007]    d) a keyed mechanism mounted in the lock body engaged with the release member such that upon the keyed mechanism being unlocked the release member is sufficiently moveable against the prong retainer to move it to a prong disengaging position.  
           [0008]    On typical North American 3-prong polarized plugs, the ground prong is cylindrical with a rounded tip, while the AC current prongs are substantially flat and have holes adjacent to their tips, allowing the prong retainer of the present invention to be effective by having a knob mounted on a flange of the prong retainer, the knob positioned on the flange such that the knob is pressed into a hole on the electrical prong upon the electrical prong being slid into position along the flange.  
           [0009]    In a preferred embodiment of the security cap:  
           [0010]    a) the release member comprises a release cam, the release member being rotatably mounted on a spine;  
           [0011]    b) the keyed mechanism comprises a keyed cylinder than is rotatable within the lock body upon the key releasing the mechanism;  
           [0012]    c) the prong retainer comprises a pair of knobs respectively mounted on a pair of flanges, each knob mounted in a position to engage a hole adjacent to the tip of an electrical plug prong that is inserted into the lock body.  
           [0013]    Thus a security cap that is mounted on the prongs of an electrical plug can be released by turning the key in the keyed mechanism, which rotates the keyed cylinder, which rotates the release member, such as a cam, which flexes the flanges of the prong retainer outward, thereby removing the knobs from the respective holes adjacent to the tips of the AC current electrical plug prongs. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is an isometric view of an exploded security cap of the present invention, aligned with an electrical plug.  
         [0015]    [0015]FIG. 2 is an end view of the prong retainer of the security cap.  
         [0016]    [0016]FIG. 3 is a side cross-sectional view of the prong retainer, with the keyed mechanism engaged with the release member inside the lock body, and with the prong retainer flanges in prong gripping position.  
         [0017]    [0017]FIG. 4 is the same view as FIG. 3, but with the release member twisted such that the prong retainer flanges are in a prong-releasing position.  
         [0018]    [0018]FIGS. 5 and 6 are side views of an alternative prong retainer for round prongs having no hole. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring to FIG. 1, a standard 3-prong plug  1  is shown, having a cylindrical ground prong  2  and current prongs  3  and  4  having holes  4  and  6  adjacent to their respective tips  7  and  8 . The security cap for electrical plugs comprises a lock body  10 , a keyed mechanism  11  with a key slot  29 , a release member  12 , a prong retainer  15 , and a bolt  23  having a bolt head  25  and a threaded end  34  that screws into a spine in the keyed mechanism  11  to hold the parts of the security cap together. The prong retainer  15  has a retainer base  16 , in which are mounted prong retainer flanges  18  and  19 , and retainer cylinder  22  through which the bolt  23  passes. The electrical plug&#39;s ground prong  2  would pass through the ground prong hole  17  in the retainer base  16 . The electrical plug&#39;s current prongs  3  and  4  would pass through the current prong slots  20  and  21  to abut the prong retainer flanges  18  and  19 . As the current prong  4  was being slid along the prong retainer flange  19 , the tip  8  would press against knob  30 , deflecting prong retainer flange  19  until the knob  30  was pressed into hole  6  on the current prong  4 . A like knob on prong retainer flange  18  would fit into hole  5  on the current prong  3 . The release member  12  has cam surfaces  13  and  14  to enable the cam member to press against the prong retainer flanges  18  and  19  and deflect them when the release member  12  is rotated between them, thereby removing the knob  30  from the hole  6  on the current prong  4  for detachment of the security cap from the electrical plug.  
         [0020]    Still referring to FIG. 1, the release member  12  has a stop flange  26  with sides  27  and  28  that abut current prong  18  or  19  respectively, depending on the position of rotation of the release member. The stop flange  26  thereby constrains the degree of possible rotation of the release member  12 , and defines both the lock position and the unlock position of the release member.  
         [0021]    Referring to FIG. 2, the retainer base  16  has a ground prong hole  17  and current prong slots  20  and  21  on either side of the retainer cylinder  22 . Current prong slot  21  is longer than current prong slot  20 , to accommodate the wider tip of the corresponding prong in a typical asymmetrically shaped set of current prongs on a polarized electrical plug. The knobs  30  and  40  are shown in the pathway defined by the current prong slots  21  and  20  respectively.  
         [0022]    Referring to FIGS. 3 and 4, from the retainer base  16  extend perpendicularly prong retainer flanges  18  and  19 , having knobs  40  and  30  respectively. The knobs  40  and  30  have angled surfaces  51  and  52  that cause the prong retainer flanges  18  and  19  to deflect when the current prongs are slid along the prong retainer flanges  18  and  19 . Once the knobs  40  and  30  are in the holes in the respective current prongs however, stop surfaces  53  and  54  at right angles to the respective prong retainer flanges  18  and  19 , prevent the current prong from being withdrawn until the prong retainer flanges are again deflected, this time by means of the release member&#39;s rotation. The retainer cylinder  22  has an inner shaft wall  41  to fit the bolt  23  (FIG. 1) and a wider outer shaft wall  42  to contain the bolt head  25  (FIG. 1). The lock body  1  has shaft wall  70  to accommodate the prongs of the electrical plug, and an inner shaft wall  71  to fit the keyed mechanism  11 . The spine  72  in the keyed mechanism  11  has a bottom portion  73  that is tapped to receive the threaded end  24  of the bolt  23  (from FIG. 1). The keyed mechanism  11  has a squared engagement end  74  that fits within the release member  12 . In FIG. 3 the release member  3  is non-releasing position. In FIG. 4, it has been twisted by the keyed mechanism such that its cam  13  presses the prong retainer flanges  18  and  19  outward to place them in a position in which they would no longer retain the prongs of the electrical plug.  
         [0023]    Referring to FIG. 5, the retaining member can alternately comprise a gripping mechanism to retain the current prongs where the current prongs  81  and  82  are cylindrical or have no hole for a retaining knob to engage. The gripping mechanism could comprise a pair of retaining cams  61  and  62  that are compressed against an electrical plug&#39;s current prongs by release cam  60  and exert a gripping force on the prongs when a withdrawing force is applied to the electrical plug, unless the keyed mechanism is in a position such that, as shown in FIG. 6, the retaining cam  60  is placed in a disengaging position and allows the gripping cams  61  and  62  to be released from the prongs. The retaining cams can have concave depressions to fit the corresponding contour of a cylindrical electrical prong.  
         [0024]    The lock body of the security cap can be shaped substantially like the body of any particular electrical plug that is desired to be secured, such that when the cap is mounted on the prongs it is substantially an extension of the plug. This will be aesthetically pleasing and will also will enable equivalent grips of the plug in one hand and the cap in the other during mounting or detachment of the security cap on or from the security cap.  
         [0025]    The parts of the security cap could be made from durable plastic or metal or a combination of suitable materials. The keyed mechanism could be a stock part, operable with a key, or it could comprise a combination lock.  
         [0026]    While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.