Abstract:
An AC line power coupling system secures a conventional plug ( 700 ) of an appliance cord or extension cord ( 702 ). A adapter ( 400 ) is fitted onto the prongs ( 704 ) of the cord, and semi-permanently attached with a connector ( 300 ) including two half housings ( 301  and  302 ) that fasten over the plug and a clamp ( 200 ) that holds the cord. The adapter prongs mate, which have a conventional layout, with a special socket ( 600 ). The adapter is locked onto the socket by a sleeve ( 500 ). The sleeve moves relative to the socket, rotating and axially sliding. When the sleeve is slid onto the protruding cylindrical end of the adapter and rotated, lugs on the inside of the sleeve engage in grooves, locking the adapter to the socket; the sleeve motion is reversed to unlock. The adapter can be plugged into conventional sockets while the connector remains fastened over the plug, but when plugged into the special socket and locked, the cord is prevented from pulling out under tension. The special socket can be adapted to junction boxes as well as to power cords.

Description:
This application is a divisional application of non-provisional application Ser. No. 09/643,234, filed Aug. 22, 2000; issued as U.S. Pat. No. 6,454,576 on Sep. 24, 2002; the full disclosure and drawings of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to locking electrical connectors, especially for power cords using the standard two-prong or three-prong arrangement with two straight blade prongs and a round prong for the ground connection on the plug, with a mechanisms or means to prevent the plug from being pulled out of the socket. 
     2. Description of the Prior Art 
     A common problem with power tools is that the power is interrupted by the extension cord being pulled out. The prongs of a conventional power plug are held by the female receptacle, or socket, with friction alone. This friction cannot be too great, lest the connection be too difficult to make and disassemble by hand; but the limited friction force cannot hold against ordinary forces on an extension cord which are encountered in the workplace, or elsewhere that electrical appliances are moved or that cords may be pulled on. 
     Because of the weight of an extension cord, and the friction of the cord&#39;s insulation, there is much greater force on the appliance end of an extension cord, or chain of cords, than at the wall socket end. Separation usually occurs at the female end of an extension cord. 
     Raymond Altergott et al, in U.S. Pat. No. 5,286,213, discloses an extension cord with a socket (female connector) that mates with a standard or conventional male power plug and attempts to secure the male plug, by gripping the prongs of the male plug inside the socket. The gripping is actuated by a cylindrical external sleeve on the socket; rotating the sleeve moves an internal cam mechanism and causes the two terminal blades of the plug to be grasped tightly by internal metal pieces. The tight grip of the metal pieces on the two prongs makes electrical contact and mechanically grasps the prongs to resist pull-out of the plug. 
     A provisional patent application of Raymond A. Altergott and Thomas P. Masbaum, dated Jul. 21, 1995 and entitled “Locking Electrical Outlet”, illustrates in one of the drawing sheets a device very similar to FIG. 1 of the Altergott et al. &#39;213 patent, but without any external cylindrical sleeve. The relative motion is supplied by rotation of an inner socket portion relative to the housing; rather than grasping the housing and the sleeve and rotating them, the housing and plug are grasped and rotated. 
     An alternate embodiment of Altergott uses the same mechanism as is disclosed in the &#39;213 patent, mounted in a connection box instead of at the end of a power cord. 
     The Altergott device has several drawbacks. First, the retention force is limited to that of friction; there is no actual locking, because the plug can be pulled by sliding of one surface over another; no part needs to be moved aside, no ledge or step need be overcome, to separate the plug and socket. Second, all separating and bending forces are taken by the prongs, which are not always strongly seated in the body of the plug; the very forces which the device is intended to resist can damage the plug by loosening, bending, or even pulling out the prongs. It would be better if at least part of the force were to be taken by the thick plastic body of the plug, but it is not. Third, the mechanism is complex and, if made to the standards of many electrical fittings, will fail prematurely. The Altergott device is non-repairable. 
     Haag, in U.S. Pat. Nos. 5,722,847 and 5,344,333, discloses a system of joining power cords which overcomes one drawback of the Altergott device, namely the reliance on prong friction to prevent separation. Haag joins the plug and socket by screw threads. The threads are set on a “face plate” which interacts with a rotatable cylindrical sleeve, that couples housings of the plug (male portion) to the socket (female portion). Haag uses two conical housings with internal parts held in place within by screws inserted through the housing wall in a direction parallel to the axis of the cone. Cylindrical portions extend from the bases of the conical portions, and those cylindrical portions are covered the cylindrical sleeve. 
     Haag&#39;s male and female connectors are custom made. If a regular plug were mated to the female connector, there would be no resistance to separation beyond that of any plug and socket. The Haag patents do not disclose an extension cord that will mate with a conventional male power plug and securely lock to it. Because a special plug is needed for secure locking, there will always be a “weak link” in any chain of power connections. For example, if a user wishes to hook up a hand saw, there will be no more than the usual resistance to pull-out even if the sockets and all extension cords have Haag&#39;s custom socket/plug structures, because the drill saw itself will have a conventional plug that can pull out. 
     The provisional application of Raymond A. Altergott and Thomas P. Masbaum that was mentioned above discloses an extension cord female end and plug each having a cylindrical portion. These two portions align when the connection is made, and form a single cylinder. A cylindrical sleeve, with two pairs of offset lugs protruding from its inner surface, is slidable over the single cylinder. It appears in the drawing that the sleeve locks the socket and plug together with grooves in the surfaces of the cylinders and lugs on the inside of the sleeve, which slide in the grooves, moving between locked and unlocked positions as the lugs slide from one position to another in the grooves. 
     The male plug of the provisional application is specially made, with the cylindrical portion, and the grooves required for locking, being molded directly into the body of the plug. Like the Haag device, the Altergott/Masbaum device cannot lock the conventional plug of a conventional extension cord, hand drill, etc. 
     Sweatman et al., in U.S. Pat. No. 5,755,588, discloses a “retention enclosure” which is usable with a conventional plug/socket combination. After the connection is made, the socket and plug are encased inside the enclosure, which includes an upper half and a lower half. The enclosure holds the socket, the plug, and their respective cords merely with friction; there is no positive latch or locking mechanism to prevent the plug from being pulled out. 
     Sweatman&#39;s FIG. 2 shows that the enclosure is long enough that, when the friction grip on the cords is overcome by a force pulling the connection apart, the plug and socket can be pulled into the ends of the enclosure to break the connection. One of Sweatman&#39;s objects is accommodate connections “having a variety of sizes and shapes”, and thus the shorter connections cannot possible be held securely. 
     Moreover, the closure mechanism is not only weak (a snap-clasp opposite a live hinge) but it is also located in the center of the enclosure, so that the two halves can be easily sprung apart at either end of the enclosure. This weakness is related to the multiple functions of the housing: it must securely hold, but still be releasable. 
     Because the Sweatman housing closes over both socket and plug, it must be removed to separate the plug from the socket. Thus, if a worker wishes to change a saw for a drill, for example, he or she must remove the housing entirely, change the appliance plug, and then reassemble the housing over the joined connection. This is awkward and time-consuming, and sooner or later the enclosure will be lost between plug insertions. 
     The Sweatman device cannot be used with a wall socket because there is no cord attached to the female portion of a wall socket. It can only be used to join one extension cord to another extension cord. 
     Elswick, in U.S. Pat. No. 5,584,720, discloses a cord plug lock that has an internal compartment just long enough to accommodate the joined pair of socket and plug. At either end is a slot through which the cord can move to the center line, so that the joined socket and plug are held inside. Elswick&#39;s device, like Sweatman&#39;s, can be lost during plug changes. Elswick illustrates its device with sockets and plugs having rounded ends, which present a definite surface against which the internal end surfaces of Elswick&#39;s lock can bear. The more usual plug design has a strain relief, lacks a definite end surface, and could not be made secure by the Elswick device. 
     The prior art does not disclose a socket or extension cord adapted to accept and securely hold in place a conventional male plug, such as the male plug of a power tool, which permits quick plug changes for various different appliances, which attaches plugs securely without relying on friction forces alone, and which has no loose parts to be lost during plug changes. 
     SUMMARY OF THE INVENTION 
     One object of the invention is adapt any conventional power plug to be securely held and quickly exchanged with another plug in a socket, whether the socket is at the end of an extension cord, in a wall, coupled to an appliance, or elsewhere. 
     Another object is to provide a plug adapter which can be used with conventional sockets and extension cords. 
     A further object is a plug locking system with no loose parts. 
     A still further object is to provide a plug connector which can be removed from the plug. 
     The present invention provides a plug adapter and two means for securing the plug adapter, which are denoted as the lock and the connector. The lock, which should be quickly and easily released, secures the plug adapter to the socket; the second means secures the plug adapter to a conventional plug, and may be semi-permanent or even permanent. The adapter has special features for locking to the socket of the present invention, but it also can be used with a conventional socket such as a common wall outlet or the female end of a conventional extension cord. That is why the connection of the adapter to the plug can be semi-permanent, or permanent; there is no reason to take it off. 
     The adapter, by separating the two functions of securing and releasing the plug, makes it possible for each function to be done in a better manner. 
     The preferred lock is actuated by a sliding cylindrical sleeve which is not removable from the socket. It cannot be lost. 
     With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of the invention; 
     FIG. 2 is a perspective view; 
     FIG. 3 is a exploded perspective view; 
     FIG. 4 is a cut-away, partially cross-sectional view; 
     FIG. 5 is an exploded perspective view of a first component of the invention; 
     FIG. 6 is a sectioned view in direction VI—VI of FIG. 5; 
     FIG. 7 is a perspective view of a second component; 
     FIG. 8 is a side view of the second component; 
     FIG. 9 is a perspective view of a third component; 
     FIG. 10 is a side view of the third component; 
     FIG. 11 is a detailed perspective partial view of the third component and of a fourth component; 
     FIG. 12 is a cross-sectional view along lines XIX—XIX of FIG. 11; 
     FIG. 13 is a detailed perspective partial view of a fifth component; and 
     FIG. 14 is a cross-sectional view along lines XIV—XIV of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a preferred embodiment of the present invention, an extension cord system, in overview. A power cord  702  ends in a plug (male connector)  700  having a typical conventional exterior shape. The cord  702  might lead to an appliance such as a power tool, or to a socket (female connector), not shown in FIG.  1 . The invention adapts the plug  700  for quick release and locking to a special socket, but does not prevent use with conventional sockets. 
     Two prongs (terminal blades)  704  extend from a face on the body of the plug  700 , and these insert into mating receptacles (not visible in FIG. 1) in an adapter  400 . The adapter  400  has prongs  404 , internally connected, which receive the prongs  704  of the plug  700 , which in turn engage with mating receptacles (not visible in FIG. 1) in socket  600  connected at the end of a cable  602 . These are internally connected to the conductors in the cable  602 , so that power can flow between the cable  602  and the cord  702 . 
     A connector joins the plug  700  to the adapter  400 . The preferred embodiment includes two half-housings  301  and  302 , which together make up a connection housing  300 . The halves  301  and  302  are shown exploded away from their positions surrounding the adapter  400  and the plug  700 . In their assembled position (shown in FIG. 3) the housing halves  301  and  302  are preferably held together by self-tapping screws  399 . FIG. 1 shows an internal annular flange  334  of the connection housing  300 , which fits into an annular groove  434  of the adapter  400 . 
     On the end of the socket  600  opposite to the cable  602  is a coupling sleeve  500 , which is slidable and rotatable on a cylindrical portion of the socket  600 , called the first barrel. The first barrel is partially visible in FIG. 3, where the sleeve  500  is in its locking position, moved away from the cable  602 . The action of the coupling sleeve will be described below. 
     A cord clamp  200  is shown exploded out of the half-housing  302 . 
     FIG. 2 illustrates the assembled connection housing  300  with the prongs  404  of the adapter  400  ready to mate with the socket  600 , and the sleeve  500  in its retracted or reserve position. 
     FIG. 3 illustrates electrical connection made and the invention locked. The sleeve  500  is in its extended or locking position, and the cable  602  is both electrically and mechanically fixed to the cord  702 . A groove  688  in a cylindrical surface  645 , as explained below, can be seen. 
     FIG. 4 shows the housing halves  301  and  302  and the sleeve  500  in cross sectioned view but the other components in plan view. The cord clamp  200  (which is also shown exploded in FIG. 1) is shown holding the cord  702 , and the face of the plug  700  is flush against the mating face of the adapter  400  (the adapter face that is hidden in FIG.  1 ). It will be understood that the socket  600  contains female connector parts, to mate with the prongs  404 , and that these open onto the mating face of the adapter  400 . To the left of that face is the annular groove  434 ; sections of the annular flange  334 , fitting into the groove  434 , are visible at top and bottom. The adapter  400  is firmly held because the screws  399  keep the flange  334  seated in the groove  434 . 
     The lock or locking mechanism includes first surface grooves  688  in a cylindrical surface of the socket  600 , which surface is denoted as the first barrel  645 , and second surface groove  488  in a cylindrical surface of the socket adapter  400 , denoted as the second barrel  445 . The two barrels  445  and  645  are axially aligned when the connector is assembled, forming together a single cylinder, and the grooves  488 ,  688  are aligned at the mating juncture of the adapter  400  and the socket  600 , as shown in FIG.  4 . The groove alignment is ensured by the angular alignment of the barrels, due to the orientation of the prongs  404  relative to the socket  600 . 
     FIGS. 5 and 6 show, on the inside cylindrical surface of the sleeve  500 , lugs  588  which engage in the grooves  688  and  488  shown in FIG.  4 . Preferably, one or more of the lugs  588  includes a snap-depression  589  that mates with a snap-ridge  689  raised from the bottom of one of the grooves. The snap-ridge  689  is preferably located in a position such that snap-in engagement takes place when the sleeve  500  is in a locking position. If desired, a snap-ridge can also hold the sleeve in a reserve position as well. 
     FIGS. 4-6 show only half of the preferred grooves and lugs, namely those on only one side of the barrels  445 ,  645  and the sleeve  500 . Similarly grooves and lugs may be on the other side which is not visible. The bilateral structure is visible in FIGS. 7-10, discussed below. 
     It will be apparent from a study of FIG. 4 that when the sleeve  500  is in the position of 
     FIG. 2, one of the lugs  588  will be seated at the end of the vertical portion of the groove  688 , that is left-most in FIG. 4; and that the sleeve  500  will be held from moving to the right. The second lug  588  is, at the same time, in the next vertical groove  688 . If the sleeve  500  is then rotated so that the first lug  588  moves down in FIG. 4, it reaches a position from which it can move to the right along the generally horizontal groove. At the same time, the second lug is poised to move along another horizontal groove (keeping in mind that the relative positions of the lugs will be opposite to that shown in FIG. 6, because the lugs engaging the grooves of 
     FIG. 4 are on the other side of the sleeve  500  from those shown in FIG. 6, and the lug on the right is thus higher instead of lower). So, the user can twist the sleeve  500  and slide it to the right. 
     As the sleeve  500  slides to the right, the right-hand lug  588  moves across the border between the first barrel  645  and the second barrel  445 , and traverses from the groove  688  to the groove  488 . Then, a second twist of the sleeve  500  by the user causes the second or right-hand lug  588  to move downward in FIG. 4 to the bottom of the vertical portion of the groove  488 . Because the left-hand lug  588  is within the groove  688 , the adapter  400  cannot be retracted from the socket  600 : the adapter  400  is locked to the socket  600 . Thus, the conductor cable  602  is securely but releasably locked to the power cord  702 . 
     To aide the user in relatively rotating the sleeve  500 , the socket  600 , and the housing  300 , each of these parts is preferably provided with knurling in the form of axially-oriented ridges  510 ,  610 , and  310 . Indicia of various positions of the sleeve, such as the reserve and locked positions, can be provided. For example, the knurling  310  on the housing  300  and the knurling  510  on the sleeve  500  may each be interrupted over a short arc, so that alignment of these knurling gaps serves as a marker for the locked position. The gaps are shown in FIG.  3 . 
     The second barrel  445  is preferably the same diameter as the first barrel  645 , but need not be (the sleeve  500  can include an internal step, for instance). However, it is preferred that the second barrel  445  be shaped such that the adapter can mate with conventional sockets, as well as with the socket  600  of the present invention. Then, the housing  300  will not need to be removed before using the appliance (not shown) connected to the cord  702 . Moreover, the housing  300  is preferably compact enough that the invention can be used with sockets as closely spaced as those of an ordinary two-gang or four-gang wall socket. 
     The preferred outline shape of the lugs  588  is trapezoidal or diamond-shaped, as shown, because that maximizes the bearing length along a circumference. However, the lugs may be of any shape that will negotiate the grooves  688  and  488 . 
     FIGS. 7-10 show the structures also shown in FIG.  4 . In FIGS. 7 and 8 double grooves  688  are visible. These are preferably bilaterally symmetrical. The snap-ridges  689  at either end of the groove  688  nearest to the mating face serve to engage the snap-depression  589  and to lock the sleeve  500  (not shown in FIGS. 7-10) into its reserve and locking positions. 
     FIG. 9 shows one of the two grooves  488  in the second barrel  445 , and in FIG. 10 a  corner of another groove  488  is visible at the bottom. 
     FIG. 11 shows a portion of the interior of the half-housing  302  with arrows A indicating the motion of the cord clamp  200  downward onto screw pedestals  397 , where holes  297  in the cord clamp  200  slide onto the narrower upper portions of the pedestals  397 , so that the bottom of the cord clamp  200  will rest against the shoulders of the pedestals  397 . The cord clamp  200  includes four gripping splines  272 , which are of different heights h 1  and h 2 , as seen in cross-sectional FIG.  12 . With this feature, the cord  702  can be gripped more or less tightly by turning over the cord clamp  200  prior to assembling the connection housing. 
     FIG. 13 shows the upper half-housing  301  which also includes pedestals  397 . Preferably, the pedestals  397  of the lower half-housing  302  have through-holes to pass the screws  399 , but the upper pedestals  397  have blind holes for self-tapping plastic screws. The upper half-housing also includes a cord-gripping bridge  320 . 
     FIG. 14 shows the structures which grip the cord  702 . A gap d is formed between the bridge  320  and the splines  272 . That gap is adjustable to better grip the cord  702 , by inverting the cord clamp  200 . 
     In alternate embodiments of the invention the socket-to-adapter locking mechanism may take different forms, such as screw threads, latches, snap-structures, screws and so on. Most of the alternate embodiments contemplated for the present invention will include a cylindrical sleeve, but others will not. Any device, structure, or means which will releasably lock an adapter to a socket is within the scope of the present invention. 
     Similarly, the connection housing  300  may be embodied in different ways. Any housing or other connector which will releasably lock an adapter to a plug is within the scope of the present invention. The connection housing  300  may be replaced by a device of open design, one that grips only the body of the plug  700 , or one that grips only the cord  702 . 
     The present invention can be used with a gang-box extension cord, where the gang-box with sockets is massive enough to hinder movements that might pull out its male plug. Such a gang-box can also include mechanical hold-down means, such as a bracket or tab that takes a hold-down screw. The invention as embodied above can be used on a wall socket or the like with appropriate modification of the socket portion. In that embodiment the cable will be the cable feeding the socket, which may be permanently installed in a wall or in a conduit, and the socket body may be a regular metal or plastic connection box. 
     The concept of the present invention is intended primarily for AC line grid power cables, but it is not restricted to AC grid power lines. It can be used for signal connectors and for couplings for different voltages, DC as well as AC, and so on. 
     Although certain presently preferred embodiments of the present invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law. 
     Infinitive verbs (e.g., “to cover”) in the following claims are intended not to invoke 35 U.S.C. § 112, 6th paragraph, and to differ from language which would invoke 35 U.S.C., 6th paragraph (e.g., “means for covering”).