Patent Publication Number: US-6220885-B1

Title: Safety locking system for electrical plugs

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of electrical conduction mechanisms for delivering electricity to homes and businesses. More specifically the present invention relates to a cord plug engagement apparatus such as a wall outlet for receiving and engaging prongs of appliance cord plugs and delivering electric current into at least one of the prongs, the apparatus having locking means which lock the prongs into the apparatus to prevent plug removal and insertion of objects by children. The essential elements of the apparatus are a face plate having prong passing ports and a face plate front surface and a face plate rear surface, a slide bolt structure constrained by mounting means on the face plate rear surface to slide parallel to the face plate, with locking bolts which slide to enter prong openings at the prong free ends and thus to lock the prongs within the apparatus, and a slide bolt structure displacement mechanism for manual movement by a user which in turn moves the slide bolt structure so that the bolts enter or retract from the prong openings. A bolt stop structure is optionally provided which obstructs the movement of the bolts across the prong entry paths prior to insertion of prongs into the apparatus, so that the prongs do not strike and damage the bolts during insertion. 
     2. Description of the Prior Art 
     There have long been plug prong engaging receptors such as outlets for releasibly holding the prongs of a cord plug within the outlet. These prior outlets and related structures have been in general inefficient and costly. 
     One such prior receptor is that of Ursich, U.S. Pat. No. 5,129,836, issued on Jul. 14, 1992. Ursich includes locking elements that are uniquely arranged to engage the typical punch holes provided in the male prongs of an electrical plug. Without other tools, the locking elements of the invention are locked in position by depression of an exterior arranged actuator which is also used to permit the plug to be easily removed. 
     Burke, Jr., U.S. Pat. No. 5,073,122, issued on Dec. 17, 1991, discloses a lock-out enclosure for power connectors. Burke, Jr. includes a tubular enclosure that is only slightly larger than the connector. A cap is installed on one end of the tubular enclosure. Installation of the cap onto the power line is made possible by a radial slot extending part way therethrough. After the cap is located on the power line, the tubular enclosure is slid over the connector and onto the cap. The cap is then permanently attached to the tubular enclosure using the adhesive or locking means to form an enclosure locking assembly. The enclosure assembly is slid over the associated connector to prevent access to the connector. 
     Boyer, U.S. Pat. No. 5,055,057, issued on Oct. 8, 1991, reveals an electric plug lock. Boyer includes a device which has bolt portions which removably slide into the openings provided at the distal end of virtually all cord plug prongs to lock the plug prongs into the device. Ursich, U.S. Pat. No. 5,281,162, issued on Jan. 25, 1994, discloses another variation of the prong opening engaging bolts in a receptor, which in this instance are metal balls which ride into the prong openings upon lock engagement. 
     Other generally related art includes Sleverman, U.S. Pat. No. 4,812,131, issued on Mar. 14, 1989 for an electrical plug apparatus; Belsky, U.S. Pat. No. 4,957,446, issued on Sep. 18, 1990, for a lockout device for electrically operated equipment; Herbert, U.S. Pat. No. 5,176,527, issued on Jan. 5, 1993, for an apparatus for preventing the use of an electrical device; Brend, U.S. Pat. No. 5,330,361, issued on Jul. 19, 1994, for an electrical plug locking device; Perkins, et al., U.S. Pat. No. 5,409,393, issued on Apr. 25, 1995, for a locking mechanism for a ribbon cord; Aikens, U.S. Pat. No. 5,666,829, issued on Sep. 16, 1997, for a plug lock; Garrison, U.S. Pat. No. 5,480,318, issued on Jan. 2, 1996 for a childproof electrical plug; and Reed, U.S. Pat. No. 5,941,724, issued on Aug. 24, 1999, for a lockable female electrical receptacle. 
     It is thus an object of the present invention to provide a safety locking system which may take the form of plug prong engaging outlet, to prevent removal of the plug from the outlet by children and the consequent danger of insertion of some other object into the outlet. 
     It is another object of the present invention to provide such a locking system and apparatus which accepts conventional, standard plugs, so that no modification need by made to the vast numbers of existing appliance cords in use today. 
     It is still another object of the present invention to provide a locking system and apparatus which includes means for retracting electrical contacts out of the plug prong entry paths of plug prongs when the apparatus is not in use so that a foreign object fitted into any of the apparatus plug prong entry paths, such as by a child, does not make electrical contact and therefore does not cause injury. 
     It is finally an object of the present invention to provide such a system and apparatus which is relatively inexpensive to manufacture and which is sturdy, durable and easy to use. 
     SUMMARY OF THE INVENTION 
     The present invention accomplishes the above-stated objectives, as well as others, as may be determined by a fair reading and interpretation of the entire specification. 
     A plug engagement apparatus is provided for engaging and conducting electricity into an electric plug having plug prongs, the prongs having prong free ends with prong openings, the apparatus including a prong retaining mechanism for receiving and retaining at least one of the plug prongs; and a slide bolt structure including at least one locking bolt and a locking bolt constraining structure for constraining the locking bolt to slide relative to the prong retaining mechanism and into the prong opening in the plug prong, so that the plug prong is engaged against removal from the prong retaining mechanism, and where the locking bolt constraining structure constrains the locking bolt to slide relative to the prong retaining mechanism and out of the prong opening in the plug prong, so that the plug prong is released and removable from the prong retaining mechanism; where the locking bolt constraining structure includes a mounting structure, so that the locking bolt constraining structure constrains the slide bolt structure to slide relative to the face plate, so that the locking bolt slides to enter the prong opening and thus locks the at least one prong within the apparatus. 
     The prong retaining mechanism optionally includes an outlet face plate having a face plate prong passing port for each plug prong, and a face plate front surface and a face plate rear surface. The plug engagement apparatus preferably additionally includes a slide bolt structure displacement mechanism for manual movement by a user which in turn moves the locking bolt to enter and to retract from the prong opening. The apparatus preferably still additionally includes a bolt stop structure for obstructing movement of the locking bolt into the path of a prong entering the apparatus. 
     The slide bolt structure preferably includes two of the locking bolts for engaging two prong openings, and the face plate preferably includes a face plate securing structure for securing the face plate against a building wall; at least two tubular prong passageways protruding perpendicular to and rearwardly from the face plate rear surface, encircling the prong passing ports, the passageways being sized in diameter to fit around and thus to receive plug prongs, and being sized in length to permit free ends of the plug prongs to extend beyond and protrude rearwardly out of the passageways. 
     The locking bolt constraining structure includes a slide bolt structure support flange extending rearwardly from the face plate rear surface. The slide bolt structure support flange preferably extends around the prong passageways in a substantially circular configuration. The slide bolt structure preferably includes two of the locking bolts for engaging two prong openings and the slide bolt structure preferably includes a pair of opposing guide channels protruding rearwardly from the face plate rear surface and opening toward each other; a bolt slide panel including a central panel portion and having two guide slats protruding from opposing edges of the central panel portion and fitting into the guide channels, the guide slats having a length so that the bolt structure has room within the guide channels to slide laterally within the guide channels; and first and second electrical terminals laterally spaced apart from each other and secured to the bolt slide plate in electrical contact with the locking bolts so that the locking bolts protrude laterally from the terminals and are slidable simultaneously into and out of the prong openings; the electrical terminals being connectable to electrical wires external to the apparatus. 
     The apparatus preferably additionally includes a generally U-shaped resilient prong engagement clip having a clip port which fits around one of the locking bolts and is secured to the bolt slide panel; so that when the slide bolt structure is slid laterally within the guide channels toward the prongs, the locking bolts pass through the prong openings and the engagement clips simultaneously bear against corresponding prongs and snap over the prongs to enhance electrical conductive contact between the terminals and the prongs. The slide panel preferably has a stem port and the slide bolt structure displacement mechanism preferably includes curved slots forming segments of a circle in the face plate, surrounding the prong openings; an annular plate placed against the face plate front surface, and connected to the face plate with an annular plate guide structure constraining the annular plate to slide in rotation about the center of the annular plate, and at least one engagement leg protruding perpendicularly from the annular plate and rearwardly through the curved slot, protruding into the stem port in the slide panel, so that rotation of the annular plate by a user causes the at least one engagement leg to bear against the slide panel through the stem port and thereby to slide the slide panel and slide the locking bolts into and out of the prong openings. The annular plate preferably includes a forwardly extending gripping tab for engagement by user fingers to rotate the annular plate. 
     The bolt stop structure preferably includes a slat opening in each of the guide channels; and an anchor bar having two opposing anchor bar ends, each anchor bar end being bent to engagingly snap into one of the slat openings so that the anchor bar extends between the guide channels, the anchor bar having two substantially parallel and laterally spaced apart resilient stop arms extending from the anchor bar obstructing movement of the locking bolts behind the passageways when no prongs are in the passageways; so that as the prongs are inserted into the passageways, the prongs bear against and deflect the stop arms rearwardly and out of the paths of and locking bolts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, advantages, and features of the invention will become apparent to those skilled in the art from the following discussion taken in conjunction with the following drawings, in which: 
     FIG. 1 is a front perspective view of the inventive apparatus showing the outlet face plate forward surface, the annular plate and tabs for operating the apparatus to lock and to release the prongs of a cord plug. 
     FIG. 2 is a perspective view of a conventional cord plug which the apparatus is intended to receive and engage. 
     FIG. 3 is a side plan view of the apparatus, showing a conventional cord plug engagingly inserted into the apparatus. 
     FIG. 4 is a rear, perspective view of the preferred embodiment of the apparatus, showing details of the slide bolt structure, the slide bolt structure displacement mechanism and the bolt stop structure. 
     FIG. 5 is an exploded, perspective view of the apparatus, showing how the various essential structures fit together. 
     FIG. 6 is a rear, perspective view as in FIG. 4 with the elements not molded integrally with the face plate removed. 
     FIG. 7 is a perspective view of the slide bolt structure and attached terminals. 
     FIG. 8 is a close-up perspective view of one of the prong engagement clips which enhance electrical contact between the plug prongs and the outlet terminals. 
     FIG. 9 is a close-up perspective view of the integrally formed portions of the slide bolt structure displacement mechanism. 
     FIG. 10 is a close-up perspective view of the integrally formed portions of the bolt stop structure, including the anchor bar and stop arms. 
     FIG. 11 is a view as in FIG. 4, but broken away and shown up close. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     Reference is now made to the drawings, wherein like characteristics and features of the present invention shown in the various FIGURES are designated by the same reference numerals. 
     First Preferred Embodiment 
     Referring to FIGS. 1-11, a plug engaging apparatus which preferably is configured as a wall outlet  10  is disclosed for receiving and delivering electric current into prongs P of an appliance cord plug C. Outlet  10  includes locking means which lock the prongs P into the outlet  10  to prevent removal of the prongs P and insertion of objects by children and to prevent inadvertent plug C removal, such as when an appliance cord is pulled taut during appliance use. 
     Outlet  10  includes an outlet face plate  60  having prong passing ports  62  and a face plate front surface  64  and a face plate rear surface  66 , locking means in the form of a slide bolt structure  20  constrained by locking bolt constraining means including mounting means  22  on the face plate rear surface  66  to slide parallel to the face plate  60 , the slide bolt structure  20  having locking bolts  30  which slide to enter prong openings O at the prong P free ends and thus to lock the prongs P within the outlet  10 , a slide bolt structure displacement mechanism  40  for manual movement by the user which in turn moves the slide bolt structure  20  so that the bolts  30  enter or retract from the prong openings O. A bolt stop structure  100  is optionally provided which obstructs the movement of the bolts  30  across the prong entry paths prior to insertion of prongs P into the outlet  10 , so that the prongs P do not strike and damage the bolts  30  during prong P insertion. 
     Face plate  60  is preferably a standard sized rectangular outlet face plate having standard anchor screw ports  68  at its longitudinal ends, and having a periphery flange  72  protruding rearwardly from its peripheral edge to abut a building wall surface W surrounding a wall outlet opening. At least two and preferably three tubular prong passageways  74  are integrally molded with and protrude perpendicular to and rearwardly from the face plate rear surface  66 , encircling the prong passing ports  62 . These passageways  74  are sized in diameter to closely fit around and thus receive standard plug prongs P, and are sized in length to permit the free ends of standard prongs P to extend beyond and protrude rearwardly out of the passageways  74  so that prong openings O are exposed. A slide bolt structure support flange  76  extends rearwardly from the face plate rear surface  66 , preferably in a broken, circular configuration around all of the prong passageways  74 . 
     The slide bolt structure  20  preferably includes a pair of opposing guide channels  24  protruding rearwardly and perpendicularly from rear surface  66  and opening toward each other. A bolt slide panel  26 , which is preferably substantially circular, includes two guide slats  28  protruding perpendicularly from the plane of the slide panel  26  at opposing panel  26  edges, and these guide slats  28  fit into the guide channels  24  and are spaced apart from each other a certain distance relative to the spacing of the guide channels  24  such that there is space for the bolt structure  20  to slide laterally within the guide channels  24 . Sections of the circular bolt slide panel  26  are cut away to leave a prong abutment mounting edge  32  and to leave a parallel terminal mounting arm  34 , and a first linear metal terminal  36  is secured within a slit in the slide panel  26  extending along the mounting edge  32  and a second linear metal terminal  38  is secured within a slit in the arm  34 . A locking bolt  30  protrudes laterally from each terminal  36  and  38 , through and out of the bolt slide panel  26  the two bolts  30  protruding in the same direction so that they can be slid simultaneously into and out of prong openings O. A generally U-shaped resilient prong engagement clip  82  has a clip port  84  which fits around each of the bolts  30  and is bonded to the slide panel  26 . When the slide bolt structure  20  is slid laterally within the guide channels  24  into a locking position, the locking bolts  30  enter the prong openings O and the side portions of the engagement clips  82  simultaneously spread as they bear against their respective prongs P and snap over the prongs P to enhance electrical conductive contact between the terminals  36  and  38  and the prongs P. The electrical terminals  36  and  38  extend out of the outer edge of the bolt slide panel  26  and are secured to a fixed terminal connection flange  86 , formed integrally with the face plate  60 , with combination rivet/screw anchor structures (not shown). Electrical harness wires (not shown) from within wall conduits (not shown) are screwed to the rivet/screw anchor structures  88  and thus are placed in electrical contact with the terminals  36  and  38 . 
     The slide bolt structure displacement mechanism  40  preferably includes curved slots  42  forming segments of a circle in the face plate  60 , surrounding the prong passing ports  62 . The displacement mechanism  40  further includes an annular plate  44  for placement against the face plate front surface  64 , the annular plate  44  having perpendicular engagement legs  46  protruding rearwardly through the curved slots  42  into the outlet box (not shown). The engagement legs  46  have rearwardly extending leg stems  48  at the rearward free ends which protrude through stem ports  50  in the slide panel  26 . The annular plate  44  has finger tabs  52  at opposing points along the annular plate  44  which protrude forwardly for gripping by a user. 
     The bolt stop structure  100  preferably includes a resilient, elongate anchor bar  102  having two bent longitudinal bar ends  104 , each of which engagingly snaps into a slat opening  106  in one of the guide channels. Two parallel and laterally spaced apart resilient stop arms  108  extend perpendicularly from the anchor bar  102  over the rearward ends of the prong passageways  74  and obstruct movement of the locking bolts  30  across the open passageway  74  free ends when no prongs P are in the passageways  74 . As prongs P are inserted into each passageway  74 , the prong P free ends bear against and deflect the stop arms  108  rearwardly, and out of the paths of the locking bolts  30 . 
     Thus to set the outlet  10  lock, the user inserts the prongs P of a plug through the plate prong passing ports  62  and through the passageways  74  so that the prongs P deflect the stop arms  108  and to place the prong openings O into alignment with the locking bolts  30 . Then the user grips the finger tabs  52  and rotates the annular plate  44  about the center point of the plate  44  and relative to the face plate  60 , thereby causing the legs  46  and leg stems  48  to slide the slide panel  26  within the guide channels  24  so that the bolts  30  enter the prong openings O. Rotating the annular plate  44  in the opposite rotational direction causes the leg stems  48  to slide the slide panel  26  in the opposite direction so that the bolts  30  slide out of the prong openings O, thereby freeing the prongs P so that the plug C may be pulled out of outlet  10 . 
     While the invention has been described, disclosed, illustrated and shown in various terms or certain embodiments or modifications which it has assumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.