Abstract:
An electrical plug is disclosed with a slidable earth pin that can be manually positioned in a stored position in a plug body of the electrical plug when the electrical plug is not in use. The slidable earth pin is movable in the channel and retained by an interlocking mechanism between the earth pin and the channel on the plug body. The earth pin has a pair of protruding fingers that snap into a first set of grooves in the channel of the plug body in a first position, and that snap into a second set of grooves in the channel of the plug body in a second or stored position. When the earth pin is in its stored position, the physical dimension of the plug is significantly more compact than conventional three pin plugs.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. provisional application Ser. No. 60/605,793 filed Aug. 30, 2004. 

   FIELD OF INVENTION 
   The invention relates generally to electrical plugs and more particularly to electrical plugs having movable earth pins. 
   BACKGROUND OF THE INVENTION 
   A wide variety of electrical devices typically draw AC power from a commercial source, usually delivered through a wall receptacle or socket, via a corresponding electrical plug. 
   A conventional electrical plug typically has a pair of conductive power pins for insertion into corresponding female connectors in the socket. The plug typically also includes an earth or ground pin that is inserted into a corresponding female connector in the socket that is coupled to ground. In one or more countries, the earth pin is slightly longer than the power pins and also functions to open a spring loaded shutter in the socket, to allow insertion of the power pins into their respective female connectors in the socket. This safety feature thus requires that an earth pin be included in all plugs even when there is no need for a ground connection. 
   Battery chargers comprise one type of electrical device whose plugs typically do not require an earth or ground connection. However, to provide the shutter opening function, a dummy ground pin still needs to be provided. Such prior art earth pins are usually in a fixed position on the electrical plug, which makes the electrical plug unnecessarily bulky. 
   One prior art method for repositioning the earth pin in an electrical plug is to connect the earth pin to a hinge, to enable the pin to be rotated between two positions, an open position and a stored position. The pin is rotated 90° between these two positions about the axis of the hinge. 
   Consumers of electrical products in recent times have shown a desire for more compact designs. Accordingly, there is a need to reduce the amount of space taken up by an electrical plug when not in use, to enable the plug to be more compact. 
   SUMMARY OF THE INVENTION 
   The present invention describes an electrical plug with a slidable earth pin that can be moved into the body of the electrical plug when the electrical plug is not in use. The electrical plug has a slidable earth pin that is positioned in a channel formed in the plug body. The earth pin has a pair of fingers that snap into a first set of grooves in the channel of the plug body to position the earth pin in a first or functional position. The pair of fingers can also snap into a second set of grooves in the channel of the plug body to position the earth pin in a second or stored position. When the earth pin is slid into its stored position, the physical dimension of the electrical plug is significantly reduced, thereby providing a more convenient and compact electrical plug. 
   Broadly stated, an electrical plug according to the present invention comprises a plug body, a first conductive blade; a second conductive blade; an earth pin having a first finger and a second finger; a channel having a first left snap groove and a first right snap groove for enabling the earth pin to be retained in a first position, and having a second left snap groove and a second right snap groove for enabling the earth pin to be retained in a second position; and wherein the earth pin can be slidably positioned such that said fingers can be manually positioned in respective first snap grooves or in respective second snap grooves. In one embodiment, the earth pin is not removable with a force less than a specified safety norm after the earth pin has been inserted. Advantageously, the present invention provides an electrical plug design that reduces the physical dimension of the electrical plug when not in use. 
   Other structures and methods regarding the present invention are disclosed in the detailed description below. This summary does not purport to define the invention. These and other embodiments, features, aspects, and advantages of the invention will become better understood with regard to the following description, appended claims and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A–1B  illustrates perspective views of a slidable earth pin plug in accordance with a first embodiment of the present invention. 
       FIG. 2A  illustrates a sectional view of the slidable earth pin plug in a first or functional position; and  FIG. 2B  illustrates a sectional view of the slidable earth pin plug in a second or stored position of the earth pin in accordance with the first embodiment of the present invention with the front panel removed. 
       FIG. 3  illustrates the assembly of the slidable earth pin plug in accordance with the first embodiment of the present invention with the front panel removed. 
       FIGS. 4A–4B  are detailed perspective views respectively illustrating the slidable earth pin and its sliding contact fingers and the assembly of the slidable earth pin plug in accordance with the first embodiment of the present invention. 
       FIG. 5A  is a detailed perspective view illustrating an earth pin and its sliding contact fingers for a slidable earth pin plug in accordance with a second embodiment of the present invention;  FIG. 5B  is a perspective rear view and  5 C is a rear view illustrating the earth pin of  FIG. 5A  assembled in the slidable earth pin plug in accordance with the second embodiment of present invention with the back panel removed. 
       FIGS. 6A–6B  are respective side and front views of the slidable earth pin plug in accordance with the first embodiment of the present invention. 
     Reference symbols or names are used in the figures to indicate certain components, aspects or features therein, with reference symbols common to more than one figure indicating like components, aspects of features shown therein. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to  FIGS. 1A–1B , there are shown perspective views of a slidable earth pin plug  100  in accordance with a first embodiment of the present invention. The slidable earth pin plug  100  comprises a plug body  110 , a slidable earth pin  120 , including an earth pin blade  124 , and a pair of conductive blades  140 . The slidable earth pin  120  is manually slidable in a vertical direction in a channel  115  formed in the plug body  110  between the pair of conductive blades  140 , as indicted by an arrow  150  in  FIG. 1B . 
   The slidable earth pin  120  in plug  100  can be manually displaced from a first or “functional” position to a second, stored position, as shown in  FIGS. 2A and 2B , respectively. In its first position, the slidable earth pin  120  is in a position where the top end of the earth pin  120  protrudes from the plug body  110  a sufficient distance to enable the earth pin blade  124  to be in a functional position, i.e., where it can be inserted into a corresponding female connector in a socket at the same time, or in advance of when the conductive blades  140  are inserted into similar corresponding female connectors in the socket, all as specified by the plug/socket standards of the country in which the plug is to be used. In its stored position, the entire length of the slidable earth pin  120  is preferably within the channel  115  and inside the plug body  110  so that the slidable earth pin  120  does not protrude beyond a top surface  111  of the plug body  120  or beyond the bottom surface  112  of the plug body  120 . 
     FIGS. 2A–2B  also illustrate the means by which earth pin  120  is releasably retained at its respective first and second positions. Earth pin  120  includes first and second fingers  121  and  122  that are compressed slightly when earth pin  120  is first inserted into channel  115 , as described in greater detail below. In its first position, as shown in  FIG. 2A , earth pin  120  is retained in channel  115  by a first left snap groove  130   a  wherein the first finger  121  is positioned, and by a first right snap groove  130   b  wherein the second finger  122  is positioned, such that the earth pin  120  interlocks with the plug body  110 . When the electrical plug  100  is not is use, the earth pin  120  can be manually pushed down the channel  115  to a second or stored position, as shown in  FIG. 2B , and held in place by the operation of the first finger  121  snapping into a second left snap groove  135   a  and the second finger  122  snapping into a second right snap groove  135   b.    
   Note that, in its second or stowed position, earth pin  120  provides an indication that an attempted insertion of plug  100  into a socket is incorrect. That is, in its second position, earth pin  120  protrudes out from plug body  110  in the direction of conductive blades  140  in a position that will not align with a socket&#39;s ground pin socket hole, thereby preventing the insertion of plug  100  into the socket when earth pin  120  is in this position. 
   As seen in the views of the present invention shown in  FIGS. 1 and 2 , earth pin  120  is prevented from being pushed to a position below the point where first and second fingers  121  and  122  snap into second left and right grooves  135   a  and  135   b  because of the existence of a narrowing in a slot  126  formed at the front of channel  115 . This narrowing is perhaps best seen at  128  in  FIG. 3 . Consequently, as the earth pin  120  is pushed down the slot, the bottom surface of the earth pin blade  124  makes contact with surface  129  of slot  126 , thereby preventing further travel of the earth pin  120  down channel  115 . 
   As is seen in  FIGS. 2A and 2B , fingers  121  and  122 , as well as left and right grooves  130   a  and  130   b  include surfaces that enable fingers  121  and  122  to be moved out of these grooves with a modest amount of manual force applied to the earth pin  120  in the desired direction of travel. 
   In  FIG. 3 , there is a pictorial diagram illustrating a step in the assembly of the slidable earth pin plug  100  wherein the earth pin is first inserted into channel  115 . In this step, earth pin plug  100  is being inserted into the channel  115  of the plug body  110 , either manually with hand pressure or using a tool or fixture. Once inserted, the upper surfaces of grooves  130   a  and  130   b  may be shaped in a conventional way known in the art to make it difficult for the earth pin  120  to thereafter be removed from channel  115  in a direction opposite to the direction of insertion. 
   As perhaps better seen in  FIG. 3 , channel  115  includes two sets of snap grooves, a first set comprising first left snap groove  130   a  and first right snap groove  130   b , and a second set comprising second left snap groove  135   a  and second right snap groove  135   b . The narrowing of slot  126  in the area shown at  128  creates ledges  129 . 
   A detailed perspective view illustrating earth pin  120  of the first embodiment of the present invention is shown in  FIGS. 4A and 4B . As seen in these figures, earth pin  120  includes a vertical section  125  that terminates in fingers  121  and  122  (i.e., the sliding contact surface area) for sliding in the channel  115  of the plug body  110 . The compressive force of fingers  121  and  122  along the sides of channel  115  is selected so as to maintain a preferred level of sliding friction in moving the earth pin  120  up and down channel  115 . The earth pin  120  can even be inserted at a vendor as part of the post-moulding operation. Side and front views of the electrical plug  100  are shown in  FIGS. 6A and 6B . 
   In  FIGS. 4A–4B , there are shown perspective views of an edge stop  170  that is preferably formed on the top surface of earth pin  120 . This surface  170  is positioned to ensure that an end user inserts the earth pin  120  a predetermined distance into an electrical outlet (not shown), and no farther. 
   Turning now to  FIG. 5A , there is shown a detailed perspective view illustrating an earth pin  500  and its first and second sliding contact fingers according to a second embodiment of the present invention.  FIG. 5B and 5C  illustrate the slidable earth pin plug with the rear removed to show the structurally different aspects of earth pin  500  as compared to earth pin  120  described above. The earth pin  500  of the second embodiment is designed with a dual lock approach, where each of the sliding contact fingers has a first set of finger locks  510  that is parallel to a second set of finger locks  512 . The first set of finger locks  510  is used for locking the earth pin  500  in slot  515  by means of ledges  518  of the upper mating grooves  522 , as seen in  FIG. 5B . The purpose of the first set of finger locks  510  is to prevent the earth pin  500  from popping out of a plug body  550  after the earth pin  500  has been inserted into the slot  515  in plug body  550 . The second set of finger locks  512 , as seen in  FIG. 5C , is used for positioning the earth pin  510  in either a folded position or an unfolded position, as well as providing the user with an indication of proper fitting between the earth pin  500  and the plug body  550  by the sounding of a click when the second set of finger locks  512  has been mated with upper mating grooves  522  or with lower mating grooves  524 . A slot  514  in the earth pin  500  is provided to impart flexibility to an arm  530  having the second set of finger locks  512 . 
   In a third embodiment of the present invention, the earth pin  120  or  500  is not removable with a force less than a specified safety norm after the earth pin  120  or  500  has been inserted. The finger locks  122  and the grooves  130   a  and  130   b  in the first embodiment, and the finger locks  510  and the ledges  518  in the second embodiment are designed to implement this safety feature of the third embodiment. 
   In a preferred embodiment, earth pin  120  or  500  is a non-conductive dummy pin for use in a battery charger or the like where there is no need for a ground connection but where the earth pin  120  or  500  is just needed to open the spring loaded shutter of the socket in which the plug is to be inserted. One of the ordinary skill in the art should recognize that the present invention can be applied to different types of electrical plugs in various regions or countries. One suitable application is on plugs as used in the United Kingdom. 
   Those skilled in the art can now appreciate from the foregoing description that the broad techniques of the embodiments of the present invention can be implemented in a variety of forms. Therefore, while the embodiments of this invention have been described in connection with particular examples thereof, the true scope of the embodiments of the invention should not be so limited since other modifications, whether explicitly provided for by the specification or implied by the specification, will become apparent to the skilled practitioner upon study of the drawings, specification, and following claims.