Abstract:
A safety shutter for a power receptacle includes two identical sliding blocks engaged with each other and two biasing members. Each sliding block has a base and a platform extending from the base with a slanted surface. The slanted surfaces are disposed below the holes of the receptacle. The biasing members are helical torsion springs disposed at the end of the sliding blocks. The platform of each sliding block is disposed above the base of the other sliding block so the shutter normally blocks access to the conductors inside the receptacle. When two prongs of a plug are inserted into both holes, the prongs push on both slanted surfaces, causing the shutter to open. When a foreign object is inserted into only one hole, only one sliding block is moved by the foreign object and the base of the other sliding block still blocks access to the conductors.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a power receptacle, and in particular, it relates to a receptacle with a safety shutter providing tamper resistance. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventional power receptacle such as wall receptacles or extension cord receptacles have one or more holes to receive plugs. The electrical conductors in open holes may corrode due to the moisture in the air, or their electrical conductivity may be affected by dust accumulation. Moreover, if used improperly, or if children play with the receptacle, conductive foreign objects may be inserted into the hole. This can cause electrical shock and is of great safety concern. 
         [0005]    To solve the above problem, tamper resistant receptacles have been developed. However, these tamper resistant receptacles have various shortcomings. 
         [0006]    For example, in the tamper resistant receptacle described in U.S. Pat. No. 4,379,607, a plastic biasing member is used at each end of the device to urge the shutter to the closed position. Such plastic biasing members tend to be unreliable as the material may become fatigued due to repeated use and various environmental factors. Thus, the elasticity of the plastic material may be lost and the shutters may fail to close. Further, the plastic biasing members are bulky and increase the overall size of the receptacle. 
         [0007]    As another example, in the tamper resistant receptacle described in U.S. Pat. No. 5,915,981, a coaxially disposed compression coil spring is used at each end of the device to urge the shutter to the closed position. Such springs also tend to be bulky. 
         [0008]    As another example, in the tamper resistant receptacle described in Chinese patent CN 99254384.3, the biasing member used in the safety mechanism is an F-shaped metal plate, which tends to become fatigued or broken due to repeated use. Further, the biasing member and the safety mechanism are installed separately, making it inconvenient to install and replace and limiting its applicability. 
         [0009]    Some other tamper resistant receptacles have complicate structures and are costly to manufacture. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed to an improved tamper resistant power receptacle. 
         [0011]    An object of the present invention is to provide a tamper resistant power receptacle that is reliable and compact and has wide applicability. 
         [0012]    Additional features and advantages of the invention will be set forth in the descriptions that follow and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings. 
         [0013]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a safety shutter for a power receptacle, which includes: two identical sliding blocks engaged with each other, wherein each sliding block includes a base having an opening and a platform extending upward and outward from a first end of the base, the platform having an outward-facing slanted surface and a rear surface opposite the slanted surface, wherein the rear surfaces of the two platforms face each other, wherein the platform of each sliding block is disposed above an upper surface of the base of the other sliding block, and wherein each sliding block has a blocking portion extending from the base to contact against the slanted surface of the other sliding block when the two sliding blocks move relative to each other in a first direction; and two helical torsion springs, one for each sliding block, wherein each helical torsion spring is disposed at a second end of the corresponding sliding block to urge the two sliding blocks to move relative to each other in the first direction. 
         [0014]    In another aspect, the present invention provides a tamper resistant power receptacle, which includes: a cover having at least two holes; a base coupled to the cover, the base including a plurality of conductors corresponding in position with the holes of the cover; and a safety shutter which includes: two identical sliding blocks engaged with each other, wherein each sliding block includes a base having an opening and a platform extending upward and outward from a first end of the base, the platform having an outward-facing slanted surface and a rear surface opposite the slanted surface, wherein the rear surfaces of the two platforms face each other, wherein the platform of each sliding block is disposed above an upper surface of the base of the other sliding block, and wherein each sliding block has a blocking portion extending from the base to contact against the slanted surface of the other sliding block when the two sliding blocks move relative to each other in a first direction, and wherein the slanted surfaces of the two sliding blocks are disposed below the two holes of the cover; and two helical torsion springs, one for each sliding block, wherein each helical torsion spring is disposed at a second end of the corresponding sliding block to urge the two sliding blocks to move relative to each other in the first direction. 
         [0015]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]    The features and advantages of the preferred embodiments can be further understood from the detailed description below with reference to the following drawings: 
           [0017]      FIG. 1  is a partial exploded perspective view of a tamper resistant power receptacle showing the safety shutters according to an embodiment of the present invention. 
           [0018]      FIGS. 2   a - 2   c  are perspective views of various components of the safety shutters of  FIG. 1 , wherein  FIG. 2   a  shows a single sliding shutter block and its biasing member,  FIG. 2   b  shows two sliding shutter blocks and their biasing members in an assembled stated, and  FIG. 2   c  shows the two sliding shutter blocks and their biasing members in a state when a foreign object is inserted. 
           [0019]      FIG. 3  is a perspective view of the safety shutters of  FIG. 1  viewed from a different direction along with the cover of the receptacle. 
           [0020]      FIG. 4  is a partial cut-away perspective view of the safety shutter installed in the receptacle. 
           [0021]      FIGS. 5   a - 5   b  illustrate the tamper resistant receptacle when no object is inserted into the hole, where  FIG. 5   b  is a cross-sectional view along the line X-X of  FIG. 5   a.    
           [0022]      FIGS. 6   a - 6   b  are cross-sectional views illustrating the tamper resistant receptacle when an object is inserted into a single hole. 
           [0023]      FIGS. 7   a - 7   b  are cross-sectional views illustrating the tamper resistant receptacle when a plug is correctly inserted into the receptacle. 
           [0024]      FIGS. 8   a - 8   b  illustrate tamper resistant receptacle according to other embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    In the drawings and the descriptions below, similar components of the embodiments are labeled with similar or the same reference symbols. In addition, the sliding mechanism is formed by two identically shaped sliding blocks cooperating with each other, and in some figures reference symbols are provided for one of the sliding blocks. 
         [0026]    Referring to  FIG. 1 , a tamper resistant receptacle incorporating a safety shutter according to embodiments of the present invention includes a cover  1  and a base  2  removably coupled to the cover. The cover  1  has hot and neutral holes  11  and a ground hole  12 . The base  2  includes hot and neutral conductors  21  and ground conductors  22  corresponding to the hot and neutral holes  11  and the ground hole  12 . The safety shutter is disposed between the cover  1  and the base  2 , preferably aligned with the hot and neutral holes  11 . The safety shutter includes two identically shaped sliding blocks  3  and corresponding biasing member. 
         [0027]      FIGS. 2   a - 2   c  show the detailed structure of the safety shutter including the sliding blocks and the biasing members. As shown in  FIG. 2   a,  the sliding block  3  includes a base  31  having an opening  38 . The opening  38  can have any suitable shape as long as it sufficiently exposes the conductor  21  of the base  2  so that the plug can go through the opening to contact the conductor  21  in a normal connection. At one end of the base  31 , a platform  32  extends upward and outward from the upper surface of the base  31 , the platform  32  having a slanted surface  321  facing upward and outward to form a wedge shape. When an object is inserted into the corresponding hole of the receptacle, the object moves downward along the slanted surface  321 , thereby pushing the sliding block  3  backward (i.e. the slanted surface  321  moves toward the rear surface  323  of the platform  32 ). In one embodiment, the slanted surface has a curved shape. 
         [0028]    Because the platform  32  is raised above the upper surface of the base  31 , when two sliding blocks  3  are coupled together, the lower surface  322  of the platform  32  of one sliding block  3  will move above the upper surface  311  of the base  31  of the other sliding block, as shown in  FIGS. 2   b  and  2   c.  To limit the range of motion of the platform  32  relative to the other sliding block  3 , a blocking portion extends from the upper surface  311  of the base  31  to contact against the slanted surface  321  of the other sliding block. In one implementation, the blocking portion is a blocking wall  35  facing the rear surface  323  of the platform  32 . In another embodiment, the blocking portion may also be a blocking block  36  disposed on a side of the base  31 . To cooperate with the blocking block  36 , the platform  32  of other sliding block  3  has a notch  37  corresponding in position with the blocking block  36  of the first sliding block  3 , such that when the two sliding blocks contact each other, the contact surface  361  of the blocking block  36  of the first sliding block is in contact against the contact surface  371  of the notch  37 . In a preferred embodiment, both the blocking wall  35  and the blocking block  36  are employed. 
         [0029]    To assemble the two sliding blocks, the platform  32  of one sliding block is disposed above the upper surface  311  of the base  31  of other sliding block. The biasing members such as springs  33  are disposed at an end of the base  31  opposite the end where the platform  32  is located. Various types of springs and various mounting methods may be used. In a preferred embodiment, the spring is a helical torsion spring. Such springs are compact and each to mount and replace. A post  34  is disposed outside of the blocking wall  35  and extends upward from the base  31  and the torsion spring  33  is disposed around the post  34 . One leg  332  of the torsion spring  332  is pressed against the blocking wall  35 , while the other leg  331  is pressed against an inner surface  13  of the cover  1  when assembled (see  FIGS. 5   a - 7   b ). The springs  33  provide the biasing force for the sliding blocks to urge the sliding blocks against each other, such that in a normal state, the lower surface  322  of the platform  32  covers the upper surface  311  of the other sliding block  3 . As a result, the shutter is closed and the conductors of the receptacle are not accessible. Also as shown in  FIGS. 2   b  and  2   c,  a protrusion  351  is formed on the outside of the blocking wall  35  such that it is located above the leg of the spring  33  that is pressed against the blocking wall to further secure the spring in its place. 
         [0030]    In the above-described preferred embodiment, the slanting surfaces  321  face the outside of the sliding blocks  3  such that the rear surfaces  323  of the platform  32  on the two sliding blocks face each other. This allows the sliding blocks to have a greater range of travel, so that even plugs with relatively thick prongs can be plugged into the receptacle, enhancing the applicability of the receptacle. Further, having the two rear surfaces  323  face each other can prevent the sliding blocks from over traveling when oversized prongs are inserted. It also prevents over compression of springs  33 . 
         [0031]      FIG. 3  shows the sliding blocks  3  and the cover  1  from a different perspective than  FIGS. 2   a - 2   c.  From  FIG. 3 , it can be seen that the platform  32  extends upward and outward from the upper surface  311  of the base  31 . (Note that the sliding blocks  3  are turned upside-down in  FIG. 3  relative to  FIGS. 2   a - 2   c .) It can also be seen that the base  31  having an opening  38  generally has a U shape, so that when the two sliding blocks are assembled, the opening correspond to the hot and neutral holes  11  of the receptacle, and the ground hole  12  does not have a shutter. This can be further seen in  FIG. 4 . In other words, the safety shutter of this embodiment emphasizes the protection of the hot and neutral holes  11  with a relatively compact and simple structure. 
         [0032]    The operation of the safety shutter is explained now with reference to  FIGS. 5   a - 7   b.    
         [0033]    In the normal state, the two sliding blocks are urged by the two springs  33  toward the center to stable positions. In this state, the lower surface  322  of the platform  32  of one sliding block  3  rests on the upper surface  311  of the base  31  of the other sliding block  3 , as shown in  FIG. 5   b.  Thus, in this state, the conductors inside the receptacle are isolated from the outside environment, minimizing the adverse effects of the environment (dust, moisture, etc.) on the conductors. 
         [0034]    When a foreign object  4  such as a metal wire, nail, a child&#39;s finger, etc. is inserted into a single hole of the receptacle, as shown in  FIGS. 6   a  and  6   b,  the foreign object  4  slides downward along the slanted surface  321  of the platform  32  of the first sliding block  31  below that hole  11 . This pushes the platform  32  toward the center, increasing the torsion on the spring  33  for the first sliding block  3 . However, the blocking wall  35  of the second sliding block  3  is urged by its spring  33  and moves in the same direction as the platform  32  of the first sliding block, so that the lower surface  322  of the platform  32  of the first sliding block  3  is always positioned above the upper surface  311  of the base  31  of the second sliding block  3 . As a result, the foreign object  4  cannot reach the conductors  21 , effectively preventing electrical shock. 
         [0035]    The normal operation of the receptacle is shown in  FIGS. 7   a  and  7   b.  When a plug  5  is properly inserted, i.e. the two prongs  51  are inserted simultaneously, and move down along the slanted surfaces  321  on both sliding blocks. The sliding blocks  3  move toward each other against the bias of the springs  33 , such that the lower surface  322  of one block no longer overlaps the upper surface  311  of the base  31  of the other sliding block. Thus, the opening  38  of the sliding blocks are exposed, allowing the prongs  51  to reach the conductors  21  to establish an electrical connection. Moreover, because the blocking walls  35  are urged by the springs  33  to return to the closed position, it makes the prongs  51  more securely inserted in the receptacle. 
         [0036]      FIGS. 8   a - 8   c  show several receptacles incorporating the safety shutter according to embodiments of the present invention. As seen in these figures, the structures of the hot and neutral holes and the ground hole may be varied according to the practical applications, and the receptacle maybe a wall mounted receptacle or a receptacle on an extension cord, while the structures of the safety shutter may be used regardless of these variations. Due to the compact structures of the safety shutter, the overall size of the receptacle is not substantially increased. For these reasons, the receptacle has wide applications. 
         [0037]    It will be apparent to those skilled in the art that various modification and variations can be made in the power receptacle of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.