Electrical receptacle with safety shutter

An electrical receptacle of the type having movable shutter members positioned to prevent insertion of objects other than electric plugs through the plug blade-receiving openings into contact with line terminals. Two identical shutter members, each having a camming portion and a blocking portion, are mutually assembled for relative, linear movement in either of two, opposite directions from a centered position to which they are biased by a pair of coil springs. Rigid objects inserted through the receptacle openings contact an angularly disposed surface on the camming portion of the shutter members, causing lateral movement of the element. When the blades of a plug are inserted, both shutter members move laterally to permit continued advance of the blades into the terminal contacts. When a single object is inserted, the blocking portion of one shutter element prevents advance of the object. A lip on the blocking portion prevents passage of the inserted object around the shutter element. Other features include compatibility of the shutter structure with existing receptacles, including those with straight straps, a one-piece spacer supporting the shutter elements for low-friction movement and ease of automated assembly.

BACKGROUND OF THE INVENTION 
The present invention relates to electrical receptacles of the type having 
slidable shutter mechanisms arranged behind the openings which receive the 
blades or prongs of an electrical plug connected to the receptacle. 
In order to prevent electrical shocks and possible injuries which may 
result from insertion of an electrically conducting member into the live 
terminals of an electrical receptacle, shutter mechanisms have been 
provided as a safety feature. The type of such mechanisms with which the 
present invention is concerned include a plurality of moveable members 
which are spring-biased to positions wherein surfaces thereof are located 
between the plug-receiving openings and the live terminals within the 
receptacle. The shutter members are moved laterally by objects inserted 
through the openings in the receptacle cover. However, the structure is 
such that the shutter members must be moved in unison, as by insertion of 
plug blades, in order to achieve physical access to and electrical 
communication with the terminals. That is, when a single shutter member is 
moved independently by insertion of a device through a single opening, the 
other shutter member remains stationary with a portion in a blocking 
position to prevent advance of the device into contact with the receptacle 
terminals. 
It is the object of the present invention to provide an electrical 
receptacle having a novel and improved safety shutter mechanism, 
overcoming a number of deficiencies of prior art mechanisms of this type. 
For example, the shutter mechanism of the present invention is more 
difficult to defeat than prior art mechanisms intended for the same 
purpose. In addition, the present shutter mechanism elements are 
configured and relatively arranged to promote automated assembly of the 
receptacle, including the shutter elements. Other objects and advantages 
will be pointed out and described in the following sections of this 
specification. 
SUMMARY OF THE INVENTION 
U.S. Pat. No. 5,472,350, of the present applicant and commonly assigned 
with the present application, discloses a duplex electrical receptacle 
having a number of unique features, including parts configured to 
facilitate fully automated assembly, a mounting strap having no bends 
other than the ground wire attachment portion, and a central opening in 
the cover exposing a surface portion of the strap to position the adjacent 
surfaces of the cover and strap in the same plane. The receptacle consists 
of a back body, mounting strap, a pair of terminals and a cover. A pair of 
contacts for receiving the grounding prongs of plugs inserted into the 
receptacle and a screw for connection of a ground wire are included with 
the strap, and a pair of screws for connection of hot and neutral wires 
are received in threaded openings in the terminals. 
Although many features of the safety shutter structure of the present 
invention may be incorporated in receptacles of other designs, the 
following detailed description is directed to incorporation of the present 
invention in the receptacle of the aforementioned patent. The back body, 
strap including the grounding contacts and ground wire screw, and the 
terminals with side screws are identical to those of the U.S. Pat. No. 
5,472,350 patent, with the cover somewhat modified for compatibility with 
the safety shutter structure. The latter comprises four, identical shutter 
elements, four springs and a spacer member. The design is such that the 
entire receptacle, including the safety shutter structure, may be 
assembled in a fully automated manner. 
The shutter elements are configured for mutual assembly in pairs, one pair 
to be placed behind each of the plug-receiving openings of the duplex 
receptacle. Structural features of the shutter elements cooperate with one 
another and with the spacer member to provide a number of unique features 
and advantages. For example, the subassembly consisting of a pair of 
shutter elements is biased by two opposing springs to a central, rest 
position from which the elements are laterally movable in both directions. 
These and other features will be specifically pointed out and described in 
detail, and thus more readily understood and fully appreciated, in the 
following Detailed Description, taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION 
Referring now to the drawings, in FIG. 1 is seen a duplex wall receptacle 
indicated generally by reference numeral 10 and containing the safety 
shutter mechanism of the invention. Visible on the exterior of receptacle 
10 in FIG. 1 are back body 12, cover 14, mounting and grounding strap 16, 
and an exposed portion of terminal 18 having threaded openings for screws 
20 by which wires of the electrical circuit which incorporates receptacle 
10 may be attached to terminal 18. Similarly, a ground wire may be 
connected to portion 16' of strap 16 by means of screw 22. Receptacle 10 
is mounted by screws 24 in conventional wall or junction box 26, and wall 
plate 28 is attached to the receptacle by screw 30. 
Elements of receptacle 10 are seen in exploded perspective in FIG. 2. In 
addition to previously mentioned back body 12, cover 14, strap 16, 
terminal 18 and screws 20 and 22, the elements comprise terminal 32 with 
screws 34, spacer member 36, coil springs 38, 38', 40 and 40', and shutter 
elements 42, 42', 44 and 44'. As previously mentioned, in the disclosed 
embodiment of receptacle 10, back body 12, strap 16, terminals 18 and 32, 
and screws 20, 22 and 34 are identical to the receptacle of U.S. Pat. No. 
5,472,350; cover 14 is somewhat modified, as explained later, and spacer 
36, springs 38, 38', 40, 40' and shutter elements 42, 42', 44, 44' have 
been added. Springs 38, 38', 40 and 40' are small coil springs, all 
identical to one another, as are shutter elements 42, 42', 44 and 44'. One 
of the shutter elements is shown individually in FIGS. 3-8, details of 
which will now be described with the purpose and function of each 
significant feature explained later. The configuration of the shutter 
elements and their cooperative relationship will be better understood with 
reference to FIGS. 9-13. 
Each shutter element is formed as a unitary, plastic molding having three 
major portions, i.e., arms 46 and 48 and side member 50. Arms 46 and 48 
extend in spaced, parallel relation from what is termed the inner surface 
of side member 50 to free, terminal ends. For reasons which will later 
become apparent, arms 46 and 48 are termed "blocking" and "camming" 
portions, respectively, of the shutter elements. Protrusion 52, having 
angled surface 54, extends from the outer surface of side member 50 at a 
position intermediate of the ends thereof. It will be understood that the 
term "angled surface" is used herein to indicate an essentially planar 
surface arranged at an acute angle with respect to what are termed the 
outer and inner planes of the shutter element, denoted by letters A and B, 
respectively, in FIGS. 3 and 7. Ledge 56 on the inner surface of side 
member 50 extends from arm 48 for a portion of the distance to arm 46. 
Portion 58 of side member 50 extends past arm 48, and stepped shoulders 60 
and 62 are formed inwardly of the free end of portion 58. Rib 63 extends 
along the edge of portion 58 from shoulder 62 to the free end. 
Arm 46 is configured to include ledge 64, extending perpendicularly from 
back wall 66 toward arm 48, and between side member 50 and upturned end 
wall 67. Lip 68 extends along the side of ledge 64 opposite and parallel 
to back wall 66. End wall 67 is spaced from the ends of back wall 66 and 
lip 68 to form groove 80. Recess 72, of generally U-shaped configuration, 
is formed in outer end surface 74 of arm 46, and ledge 76 extends along 
one side. Portion 78 of ledge 76 extends outwardly in spaced, opposed 
relation to groove 80 and end wall 67. 
Arm 48 includes angled surface 82 which is contacted by one of the plug 
blades to effect lateral movement of the shutter element during plug 
insertion, as explained later. Surface 83 is parallel to and between 
planes A and B. Shoulder 85 is contiguous with surface 83 adjacent the 
free end of arm 48. A pair of spaced protrusions 84 extend toward arm 46. 
The outer and inner surfaces of arms 46 and 48 and side member 50 lie in 
common, outer and inner planes A and B, respectively. It will be noted 
that arm 48 is shorter than arm 46. 
Turning now to FIGS. 9-13, the cooperative relationship of the structural 
features of a pair of identical, mutually assembled shutter elements will 
now be explained. Shutter elements 42 and 42' are placed in mutually 
assembled relation with side members 50, 50' outermost to form a complete 
shutter subassembly. When so assembled, the shutter elements are 
relatively moveable, with certain portions in sliding contact, between two 
terminal positions. Shutter elements 42 and 42' are shown in FIGS. 10 and 
12 in what is termed the "closed" position since they are disposed with 
surfaces 82, 82' as well as ledges 64, 64' directly between the 
plug-receiving openings in cover 14 and the female contacts of terminals 
18 and 32 when in this position within receptacle 10. When in the "open" 
position, shown in FIGS. 11 and 13, the shutter elements are removed from 
alignment with the plug-receiving openings, permitting insertion of the 
plug blades into the female contacts of terminals 18, 32, as explained 
later. 
The closed position is defined by abutting contact of shoulders 60, 60' and 
62, 62' with the opposing edges of portions 78', 78 and end walls 67', 67, 
respectively. Ribs 63, 63' are engaged in grooves 80', 80, respectively, 
as the end portions of each side member are retained between portions 78, 
78' and end walls 67, 67' of the other element. Surfaces 83, 83' are 
superposed with ledges 64, 64' and lips 68, 68'. 
During at least the major portion of relative movement of the shutter 
elements, ribs 63, 63' remain engaged in grooves 80', 80, respectively, 
with portions 58, 58' slidingly supported on the upper surface of end 
walls 67', 67, respectively. During the latter portion of movement toward 
and the initial portion of movement away from the open position, shoulders 
85, 85' are slidingly supported upon the upper surfaces of ledges 56', 56, 
respectively. The cooperative structural and functional features of the 
shutter elements, as well as the manner of their movement, will be 
returned to after individual description of the other receptacle 
components. 
Spacer member 36 is shown in detail in FIGS. 14-18. The side of spacer 36 
shown in FIG. 14 faces cover 14 in the assembled condition of the 
receptacle, and is therefore termed the top side. A first pair of 
enclosed, elongated, parallel slots 90, 90' lie between a second pair of 
slots 92, 92' at one end of spacer 36. A pair of open-ended slots 94, 94' 
lie between another pair of enclosed slots 96, 96' at the other end. When 
a plug is inserted in receptacle 10 the blades pass through slots 92, 92', 
or 96, 96', slots 92 and 96 being somewhat longer than slots 92' and 96' 
to accept the wider blade of a polarized plug. 
A pair of flexible arms 98, 98' extend integrally from the top surface of 
spacer 36 between opposite ends of slots 90, 90'. Another pair of flexible 
arms 100, 100', identical to one another and to arms 98, 98' extend from 
the top surface essentially between opposite ends of slots 94, 94'. As 
best seen in FIG. 15, the free ends of arms 98, 98' terminate in hooked 
portions directed toward one another, as do the free ends of arms 100, 
100'. Although more detailed descriptions of preferred procedures for 
assembly of receptacle 10 and relative positions of the fully assembled 
elements appear later herein, the outline in phantom lines of a shutter 
subassembly 43 retained by hooked arms 98, 98' is shown in FIG. 15. The 
position of the top surface (seen in FIG. 14) between lines 101, extending 
across the full width of spacer 36, is recessed a short distance (e.g., 
0.010") from the surface portions on each side thereof. Thus, shutter 
subassembly 43 is supported only on its lateral edges, as is apparent in 
FIG. 15, thereby reducing the frictional forces opposing sliding movement 
of the shutter elements upon the spacer surface. The same is true of the 
surface portion between lines 101' at the opposite end of spacer 36. 
A pair of U-shaped wall members 102, 102' extend from the top side of 
spacer 36 on opposite sides of slots 92, 92', and another pair of 
identical U-shaped wall members 104, 104' are positioned on opposite sides 
of slots 96, 96'. The open sides of each pair of wall members face 
inwardly toward one another. Small, flexible tabs 103, 103' are positioned 
adjacent wall members 102, 102', and tabs 105, 105' are adjacent wall 
members 104, 104'. 
Other significant features of spacer 36 include two pair of wall members 
106, 106' and 108, 108' of substantially semi-cylindrical shape extending 
integrally from the bottom side of spacer 36, essentially at the four 
corners thereof. When receptacle 10 is fully assembled, each of these wall 
members is positioned adjacent one of the female contacts of the terminal 
and serves as a stiff spring, opposing movement of the contact as a plug 
blade is inserted therein. In previously mentioned U.S. Pat. No. 5,472,350 
identical wall members were provided for the same purpose on the inner 
side of the receptacle cover. Thus, the springlike wall members and their 
useful function have been retained in the safety receptacle of the present 
invention, being moved from the cover to the spacer. Opening 110 in the 
central portion of spacer 36 lies between wall portions 112, 112' which 
are offset from the planes of the wall portions at each end to permit 
another important feature of the receptacle of the prior patent to be 
retained, as explained later. Notches 113, 113' extend into the outer 
edges of wall portions 112, 112', respectively. 
Details of cover 14 are shown in FIGS. 19-22. The usual two groups of 
through openings 114 and 116 are provided for insertion of the hot, 
neutral and ground prongs of standard electrical plugs into the 
corresponding female contacts of the duplex receptacle. The plane of 
central wall portions 118, 118', on each side of opening 120, is recessed 
from the outer surface planes of plug-receiving portions 14', as best seen 
in FIG. 22. 
On the underside (FIG. 21) of cover 14, are wall portions, recesses, etc. 
configured for nesting fit of spacer 36. Of particular note are short wall 
portions 122, 122' having terminal edges in opposed, spaced relation to 
the terminal edges of wall portions 124, 124', providing open spaces or 
pockets 123, 123' on opposite sides of openings 114. Likewise, pocket 127, 
is provided between wall portions 126 and 128, and pocket 127' between 
wall portions 126' and 128' on opposite sides of openings 116. Also, as 
seen in the sectional view of FIG. 20, small grooves 130 and 132 are 
formed in the inwardly facing surfaces of wall portions 122' and 128', 
respectively. It will be understood that identical grooves (not shown) are 
formed in wall portions 122 and 128. Semicircular protrusions 134, 134' 
are provided integrally with side wall portions 136, 136', respectively. 
The elements are configured for ease of automated assembly of receptacle 
10. A preferred method of assembling the receptacle of aforementioned U.S. 
Pat. No. 5,472,350 is disclosed in U.S. Pat. No. 5,546,657. The present 
receptacle may be assembled by essentially the same method by attaching 
the spacer, with shutter subassemblies and springs in place, to the cover 
before placing the latter in covering relation to the back body. Spacer 36 
is placed on a horizontal support and springs 38, 38' and 40, 40' are 
placed in coaxial pairs with one end of each spring in the pockets formed 
by U-shaped wall members 102, 102', 104, 104', respectively. As the 
springs are temporarily retained in position by magnets and grease sputs 
where their ends abut the U-shaped wall members, they are compressed by 
mechanical fingers sufficiently to permit placement of a shutter 
subassembly between each pair of springs. The subassemblies, in the closed 
position of FIGS. 10 and 12 and surfaces 82, 82' facing upwardly, are 
moved downwardly to rest upon the surfaces of spacer 36 between the 
springs. During such movement, the hooked ends of arms 98, 98', 100 and 
100' will be cammed outwardly by angled surfaces 54, 54' of each 
subassembly, and the natural resilience of the arms will move them back to 
engage the hooked ends over protrusions 52, 52' when the shutter 
subassemblies are fully seated, as shown in FIG. 15. The springs are then 
released and one end of each is received in recesses 72, 72' in the outer 
ends of the shutter subassemblies. As the subassemblies are moved 
downwardly, the wider clearance at the open ends of recesses 72, 72' 
provides a lead-in for positioning the ends of the springs in the closed, 
curved ends of the recesses. 
Cover 14 is then moved downwardly into mating engagement with spacer 36. 
When so positioned, U-shaped wall members 102, 102', 104, 104' are 
received in pockets 123, 123', 127, 127', and protrusions 134, 134' on the 
cover are received in notches 113, 113' of the spacer. Also, flexible tabs 
103' and 105' are received in grooves 130 and 132, respectively, and tabs 
103, 105 are received in the grooves in wall portions 123 and 128, 
providing a snap fit connection between cover 14 and spacer 36. Cover 14, 
with spacer 36 attached and the shutter subassemblies and springs 
contained between the cover and spacer, is then moved into covering 
relation with back body 12. Adjoining surfaces of back body 12 and cover 
14 are ultrasonically welded to complete permanent assembly of the 
receptacle, wherein the central surface portion of strap 16 is exposed in 
opening 120 and is coplanar with the surfaces of wall portions 118, 118' 
of cover 14. 
FIGS. 23-25 show the fully assembled receptacle in section through one of 
the shutter subassemblies and illustrate the operation thereof during both 
improper and proper utilization of the receptacle. The subassembly, 
consisting of shutter elements 42, 42', is shown in FIG. 23 in its 
centered or "rest" position wherein it is normally maintained by the equal 
biasing forces of springs 38, 38' acting upon the outer end walls of the 
subassembly. It will be noted that both the camming portion of one shutter 
element and the blocking portion of the other element are positioned 
between each of the elongated openings 114 and the female contacts of 
terminals 18 and 32 when the shutter subassembly is in its rest position. 
In FIG. 24 a screwdriver blade 138 has been inserted through one of 
openings 114, i.e., the opening on the right-hand side. As the blade is so 
moved, its tip contacts angled surface 82' of the camming portion of 
shutter element 42'. As blade 138 is advanced, the tip slides over surface 
82', camming the entire shutter element 42' toward the left as viewed in 
FIG. 24, thereby compressing spring 38'. Since the shutter elements are 
linearly moveable in either direction from the rest position, spring 38 
moves shutter element 42 a short distance toward the left until further 
movement is prevented by contact of back wall 66 of the blocking portion 
with blade 138. Spring 38 is expanded slightly in FIG. 24 from its 
position of FIG. 23, and planar (non-angled) surface 81 of the camming 
portion of shutter element 42 is in substantially covering relation to the 
one of openings 114 on the left-hand side; this effectively discourages, 
if not prevents insertion of a second device through this opening while 
the first device (blade 138) is inserted in the other opening. 
Although screwdriver blade 138 has been advanced through one of openings 
114, it cannot physically engage the female contacts or, for that matter, 
any portion of terminal 32 because further advance from the position of 
FIG. 24 is prevented by the blocking portion of shutter element 42. More 
specifically, ledge 64 of arm 46 is directly in the path of blade 138. In 
addition, and in contrast with prior art safety shutter mechanisms of this 
type, lip 68 extends along ledge 64 and serves as a barrier to any attempt 
to work blade 138, or any other foreign object, past the edge of ledge 64. 
Utilization of receptacle 10 in the intended manner is illustrated in FIG. 
25. Conventional electrical plug 140 includes male prongs 142 for 
insertion through the parallel, elongated pair of openings 114. Plug 140 
may also include a ground prong, but such is not shown in FIG. 25 since it 
has no relation to the present invention. Angled surfaces 82 and 82' are 
contacted simultaneously by the tips of prongs 142 and 142', respectively. 
As plug 140 is advanced, shutter elements 42 and 42' are moved linearly 
toward the right and left, respectively, as indicated by the horizontal 
arrows, by action of the prongs on the camming portions of the two shutter 
elements. It should be noted, and is also apparent from inspection of FIG. 
9, that the forward edges of lips 68, 68' are chamfered to provide 
additional camming surfaces for the plug prongs in the event the latter 
contact the blocking portions of the shutter elements during advance of 
the prongs into the female contacts. Both springs 38, 38' are compressed, 
and remain so until plug 140 is removed from engagement with receptacle 
10, whereupon both shutter elements are moved simultaneously by the 
springs back to the FIG. 23 rest position of the shutter subassembly. 
From the foregoing it is apparent that the present invention provides an 
electrical receptacle with safety shutter structure having many novel and 
advantageous features, including: 
a. compatibility of shutter structure with existing receptacles; 
b. incorporation of safety shutters in receptacles with straight (non-wrap 
around) straps; 
c. complete shutter-equipped receptacle conducive to automated assembly; 
d. a shutter subassembly wherein both of two shutter elements are moveable 
in either of two opposite directions from a centered position; 
e. a pair of shutter elements mounted for reciprocal, sliding movement upon 
a support surface with reduced friction; 
f. safety shutter members having anti-defeating structure, i.e., enhanced 
safety features; 
g. a one-piece spacer provides support, positioning and guiding of the 
shutter elements, as well as incorporating structure for biasing terminal 
contacts.