Abstract:
A ground power connector comprising: a plug body comprising a cavity, wherein the cavity comprises an inside dimension; a female socket positioned within the cavity, wherein the female socket comprises an outside dimension, wherein the outside dimension of the female socket is smaller than the inside dimension of the cavity; and a support of the female socket in the cavity, wherein the support allows the female socket to change positions within the cavity. A method of manufacturing a ground power connector having a female socket, the method comprising: providing an internal block comprising a cavity; inserting at least a portion of a female socket into the cavity of the internal block; sealing the cavity of the internal block; and molding a rubber plug body onto an exterior of the internal block so that the plug body flexibly supports the female socket in the cavity.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the invention relate generally to ground power connectors used on commercial and military aircraft, and more particularly to ground supply free power connectors (plugs) that control the mating and disengaging forces with aircraft fixed connectors (receptacles). 
       BACKGROUND 
       [0002]    Between flights, commercial and military aircraft typically park at a terminal facility. When parked, the aircraft engines may be powered down. Electrical power that would otherwise be supplied by the aircraft engines may be supplied by an external source, such as a ground power cart or a generator associated with a sky-bridge. A ground power connector at the end of a power supply cable couples the external power source to the aircraft. Commercial and military aircraft typically have a fixed connector somewhere on the underside near the nose landing gear. Aircraft fixed connectors comprise a receptacle with male contact pins positioned therein. Ground power connectors comprises a plug with female sockets positioned therein, wherein the plug mates with the receptacle and the female sockets mate with the male contact pins. 
         [0003]    The coupling between the ground power connector and the fixed connector is typically maintained by a physical engagement of the mating forces at both the plug/receptacle and pin/socket interfaces. The Engineering Society for Advancing Mobility Land Sea Air and Space (SAE) has promulgated an Aerospace Standard related to cable assemblies and attachable plugs for external electric power; (SAE AS7974). If the total mating forces are not sufficiently great to maintain the coupling between the aircraft fixed connector (receptacle) and the ground power connector (plug), gravitational forces will disconnect the ground power connector (plug) from the aircraft fixed connector (receptacle), and the ground power connector (plug) will drop to the ground and likely become damaged or worn. In addition to the potential for damage to the ground power connector (plug), it is undesirable for the ground power connector (plug) to prematurely disconnect from the aircraft fixed connector (receptacle), because a disconnect results in a loss of power supply to the aircraft. Electrical connectivity can also be affected my low mating forces due to low socket to pin wiping forces that will not adequately remove tarnish, oxides and corrosion form the mating surfaces which is equally undesirable. 
         [0004]    A socket contact is a female contact designed to mate to a pin or male contact. It is preferentially connected to the “power” side of a circuit where the pin is preferentially connected to the “return,” “ground” or “load” side of the circuit. There is no industry standard for this preference. It is also important for each of the individual female sockets of the ground power connector (plug) to maintain physical engagement through coupling forces with each of the corresponding individual male pins of the aircraft fixed connector (receptacle). When physical engagement through coupling forces is not maintained between a pin and a socket, electrical arcing may generate excessive resistance leading to excessive heat and increased electrical resistance to the power supply. Electrical arcing and excessive heat may prematurely damage the pin or the socket. 
         [0005]    In typical commercial and military terminal operations, ground power connectors are coupled/decoupled to/from several different aircraft each day. The simple action of inserting the ground power connector (plug) into an aircraft fixed connector (receptacle) in conventional plugs wears mating surfaces at both the plug/receptacle and pin/socket interfaces. Such wear may prevent sufficient mating forces to maintain physical engagement. Further, such wear at the pin/socket interface may lead to poor physical engagement so as to result in electrical arcing and excessive heat at one or more of the individual pin/socket interfaces. 
       SUMMARY 
       [0006]    In accordance with the teachings of the present disclosure, disadvantages and problems associated with ground power connectors have been reduced. 
         [0007]    According to one aspect of the invention, there is provided a ground power connector comprising: a plug body comprising a cavity, wherein the cavity comprises an inside dimension; a female socket positioned within the cavity, wherein the female socket comprises an outside dimension, wherein the outside dimension of the female socket is smaller than the inside dimension of the cavity; and a support of the female socket in the cavity, wherein the support allows the female socket to change positions within the cavity. 
         [0008]    A further aspect of the invention provides a ground power connector comprising: of an internal block comprising a cavity having an inside dimension suitable envelope for containing a pivot contact; a female socket positioned within the cavity, wherein the female socket comprises an outside dimension with a specified envelop allowing a pivot contact, wherein the outside dimension of the female socket is smaller than the inside dimension of the cavity, wherein the pivot contacts of the internal block and the female socket are engaged to support the female socket in the cavity so as to enable the female socket to pivot within the cavity at the pivot contacts; a female socket with a tapered bore allowing preferential alignment to bend pin contacts without introducing binding forces, and a plug body that houses the internal block and the female socket and comprises a flexible portion that flexibly seals the female socket in the cavity. 
         [0009]    Still another aspect of the invention provides a method of manufacturing a ground power connector having a female socket, the method comprising: providing an internal block comprising a cavity; inserting at least a portion of a female socket into the cavity of the internal block; sealing the cavity of the internal block; and molding a rubber plug body onto an exterior of the internal block so that the plug body flexibly supports the female socket in the cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features. Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale nor proportionally, and wherein: 
           [0011]      FIG. 1  is a perspective, exploded view of a ground power connector (plug) having a plug body, and internal block and a socket group of six sockets. In alternative embodiments, there are also connectors that have 3 contacts—2 power and 1 signal. Another configuration comprises 2 power and 4 signal socket connectors. 
           [0012]      FIG. 2A  is a perspective view of an internal block having a face section and a body section, wherein a group of a number female sockets (six are shown) are inserted into and equal number cavities in the internal block. 
           [0013]      FIG. 2B  is a perspective view of the internal block of  FIG. 2A , wherein the body section is removed to expose barrel sections of the female sockets. 
           [0014]      FIG. 2C  is a perspective view of the internal block of  FIG. 2A , wherein the face section is removed to expose tyne sections of the female sockets. 
           [0015]      FIG. 2D  is a perspective view of the socket group of  FIG. 2A , wherein the internal block is removed to expose the sockets. 
           [0016]      FIG. 2E  is a perspective view of a vertical cross-section of the internal block of  FIG. 2A , wherein the view if of the face section of the internal block so that two sockets within two respective cavities are visible. 
           [0017]      FIG. 2F  is a perspective view of a vertical cross-section of the internal block of  FIG. 2A , wherein the view if of the body section of the internal block so that two sockets within two respective cavities are visible and the pivot flange contacts are engaged with the pivot surface contacts. These pivots may also serve to seal the cavity during the molding process. 
           [0018]      FIG. 2G  is a side view of a vertical cross-section of the internal block of  FIG. 2A , wherein the view if of the nuts and bolts that fasten the face section to the body section. Any suitable fastener would be acceptable, including bonding the parts together. Another configuration would be to mold a single piece block. 
           [0019]      FIG. 3  is a perspective view of an internal block, wherein annular bevel pivot surfaces are visible at the rear openings of the cavities. 
           [0020]      FIG. 4A  is a perspective view of a female socket having a barrel section and a tyne section, wherein the female socket has a number of tynes (six are shown). 
           [0021]      FIG. 4B  is a perspective view of the female socket of  FIG. 4A , wherein a retention spring is assembled to the tynes. 
           [0022]      FIG. 4C  is a side view of the female socket of  FIG. 4A , wherein a chamfer pivot surface on a pivot flange is visible. This may also provide a seal of the cavity during a body molding process. 
           [0023]      FIG. 5A  is a perspective view of a plug body having a number of openings for access to equal number of female sockets (six openings are shown). 
           [0024]      FIG. 5B  is a perspective view of a horizontal cross section of the plug body of  FIG. 5A , wherein a void space for an internal block and socket contacts is visible. While the plug body is illustrated by itself, according to one manufacturing process, the plug body is molded directly over the internal block and contacts. 
           [0025]      FIG. 5C  is a perspective view of a vertical cross section of the plug body of  FIG. 5A , wherein a void space for an internal block is visible. 
           [0026]      FIG. 6A  is a perspective view of an arbor with an internal block mounted thereon for molding a plug body to the internal block, wherein the socket group and the internal block are fastened to the arbor in this example by COTS screws that are threaded into the sockets. Sockets and internal blocks can be fastened by other suitable methods and hardware. The arbor can be used among other manufacturing tools to form the outside housing and then is hence afterward removed. 
           [0027]      FIG. 6B  is a perspective view of a plug body molded onto an internal block and a socket group, wherein a cut-away exposes cross sections of female sockets in sealed cavities within the internal block, and wherein the view is from the back of the arbor. 
           [0028]      FIG. 6C  is a perspective view of the plug body molded onto an internal block and a socket group of  FIG. 6B , wherein the view is from the front of the arbor. 
           [0029]      FIG. 7  is a perspective view of two half-shells of a field attachable plug body and an internal block positioned between the half-shells. 
       
    
    
       [0030]    The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of exemplary embodiments of the present invention. Additionally, certain dimensions may be exaggerated to help visually convey such principles. In the drawings, reference numerals designate like or corresponding, but not necessarily identical, elements. 
       DETAILED DESCRIPTION 
       [0031]    Preferred embodiments and their advantages over the prior art are best understood by reference to  FIGS. 1 through 6C  below. However, the present disclosure may be more easily understood in the context of a high level description of certain embodiments. 
         [0032]    The ground power connectors of the present invention are intended for use at airfields, aircraft carriers, aircraft hangers and on ground power carts or other aircraft power sources. They are to be plugged into external power receptacles on aircraft to connect the aircraft to external sources of electric power. Embodiments of the present invention are directed to an approach that allows the sockets to float in an internal block. The internal block may have socket cavities designed to allow the sockets to float within the cavities. 
         [0033]    An exploded perspective view of a ground power connector (plug)  1  of the present invention is shown in  FIG. 1 . The ground power connector (plug)  1  has a plug body  10 , an internal block  20 , and a socket group  30 . In an assembled configuration, the socket group  30  is positioned within the internal block  20 , and the assembled internal block is positioned within the plug body  10 . In certain embodiments, the plug body  10  is a molded synthetic rubber outer shell that is molded around the internal components.  FIG. 1  shows two halves, but in some embodiments, the plug body is molded as a unitary whole. Alternatively, a field attachable version of this connector may have two hard plastic shells that may be filled with potting material (probably polyurethane or similar potting polymeric material), for assembly on a cable. One embodiment is to mold over the inner block, but a two piece plug body could be made with the same features.  FIG. 7  is a perspective view of two shells with and an internal block. A cable, not shown in  FIG. 1 , may be connected to the ground power connector (plug)  1  to a backside of the molded synthetic rubber plug body  10 . 
         [0034]      FIGS. 2A through 2G  illustrates various views of the internal block  20  and socket group  30 .  FIG. 2A  is an assembled perspective view of the internal block  20  and socket group  30 . The internal block  20  has a face section  21  and a body section  22 . These two sections are held together by two bolts  23  and nuts  24 . The internal block  20  has cavities that extend through both the face section  21  and the body section  22  for housing individual sockets of the socket group  30 . In particular, there are cavities for housing each individual socket, shown but not limited to: socket “N”  31 , socket “C”  32 ; socket “B”  33 , socket “E”  34 , socket “F”  35 , and socket “A”  36 . Contact identification, numbers and physical configurations vary depending on the aircraft receptacle configuration. In alternative embodiments, the internal block may be a unitary whole. Further, if the internal block is made of two or more parts, the parts may be fastened or bonded by any means known to persons of skill in the art. Bonding, ultrasonic welding, plastic stakes are all examples. 
         [0035]      FIG. 2B  is a perspective view of the internal block  20  shown in  FIG. 2A , except that the rear body section  22  of the internal block  20  is not shown. As shown, each of the sockets in the socket group  30  are positioned relatively parallel to each other within the internal block  20 . The holes in the face section  21  of the internal block are positioned relative to each other so as to correspond to the positions of male contact pins of an aircraft fixed connector (receptacle). Different plug configurations are possible depending on the aircraft receptacle configuration. 
         [0036]      FIG. 2C  is a perspective view of the internal block  20  and socket group  30  shown in  FIG. 1A , except that the face section  21  is hidden or removed. The individual sockets  31  through  36  are shown protruding from cavities  25  extending through the body section  22  of the internal block  20 . The inside diameters of the cavities  25  are larger than the outside diameters of the sockets  31  through  36  so that an annulus is defined around each of the sockets  31  through  36 . Further, each of the cavities  25  in the body section  22  have a counter-sink  26  for a receiving annular flanges  27  that extend from the back of the face section  21  (see  FIG. 2E ). 
         [0037]      FIG. 2D  is a perspective view of a socket group  30  and the nuts  24  and bolts  23  that are used to fasten the face section  21  and body section  22  of an internal block  20 , not shown. Nuts and bolts are one of several possible fastener embodiments that can be used to hold a multipiece internal block together and would not be necessary for a single piece internal block. 
         [0038]    Referring to  FIG. 2E , a perspective, cross-sectional view of the internal block  20  and socket group  30  shown in  FIG. 2A  is illustrated. The cross-section is taken vertically through the internal block  20  so as to bisect socket “F”  35  and socket “C”  32 . In this view, of the interaction between the several different annular flanges  27  and the corresponding counter-sinks  26  are visible. In particular, a secure assembly of the face section  21  to the body section  22  of the internal block  20  is facilitated when the annular flanges  27  securely insert themselves into the corresponding counter-sinks  26 . This assembly is further secured by fastening the nuts  24  to the bolts  23 . As previously described, a cavity  25  is defined in the internal block  20 . The size of the cavity  25  is sufficiently large to allow the socket to move within the cavity  25  so as to align itself with a male contact pin of an aircraft fixed connector (receptacle). In the embodiment shown in  FIGS. 2A through 2E , each of the sockets  31  through  36  are positioned within corresponding cavities  25  that are sufficiently large to allow each socket to move transversely therein. Thus, if the male contact pins of an aircraft fixed connector (receptacle) are misaligned relative to each other, so that they are no longer parallel to each other, the individual sockets  31  through  36  align themselves within their respective cavities  25  so as to mate more perfectly with the respective male contact pins. Further, each of the sockets  31  through  36  comprised an annular pivot flange  37  which engage an annular bevel pivot surface  28  at the back of the body section  22  of the internal block  20 . The interface between the annular pivot flange  37  and the annular bevel pivot surface  28  provide a support for the sockets within the cavity  25 , wherein the support is sufficiently flexible to allow the socket to move within the cavity  25 . This annular chamfer along with the socket ring make a molding seal when the sockets are drawn forward with the screws on the arbor and seated together. 
         [0039]    Referring to  FIG. 2F , a cross-sectional perspective view of the internal block  20  and socket group  30  illustrated in  FIG. 2A  is shown. Further, this cross-sectional perspective view of  FIG. 2F  is similar to that of  FIG. 2E  except that it is of the backside of the internal block rather than the front side. From this view of  FIG. 2F , the interaction between the annular pivot flange  37  and the annular bevel pivot surface  28  of each socket is plainly visible. Further,  FIGS. 2E and 2F  illustrate how the cavities  25  are tapered, such that the diameter of the cavity  25  at the end nearest the annular bevel pivot surface  28  is smaller than the diameter of the cavity  25  at the end extending into the face section  21  of the internal block  20 . The tapered holes allow the distal ends of the sockets  31  through  36 , which extend into the face section  21  of the internal block  20 , to move in transverse directions while the proximal ends of the sockets  31  through  36  are held relatively fixed by the annular bevel pivot surface  28 . Because these holes are tapered, a two-piece design of the internal block  20  enables construction via molding processes. An internal block  20  constructed of two parts may accommodate draft angles and seal the sockets front and back. The two parts of the internal block  20  may be held together with ¼-20 fasteners. The inside diameter of the sockets are also detailed to provide a taper in the opposite direction of the inner block&#39;s taper such that a bent mating pin will not bind in the back of the socket contact which is transversely fix by the pivot. 
         [0040]      FIG. 2G  is a cross-sectional top view of the internal block  20  and socket group  30  of  FIG. 2A , wherein the cross section is taken horizontally across the two nuts  24  and bolts  23 . Because this is a top view, only sockets  31  through  33  are visible. The face section  21  is connected to the body section  22  by the bolts  23  and nuts  24  to form the internal block  20 . 
         [0041]      FIG. 3  is a perspective view of a backside of the internal block  20  shown in  FIGS. 2A through 2G . At the back side of the internal block  20 , each of the annular bevel pivot surfaces  28  are clearly visible. 
         [0042]      FIG. 4A  illustrates a perspective view of one of the sockets of the socket group  30  shown in  FIGS. 1 through 2G . The socket comprises a barrel section  41  and a tyne section  42 . In the illustrated embodiment, the tyne section  42  comprises any number (six are shown) of different tynes that extend in a longitudinal direction from the barrel section  41  of the socket. The tynes from an opening  47  at their distal ends. Because the tynes in the tyne section  42  are only attached at their proximal ends to the barrel section  41 , the tynes, at their distal ends, are free to flex in radial directions. The tynes of the tyne section  42  also comprise a retention section  43  defined between a distal flange  44  and a proximal flange  45 . An annular pivot flange  37  extends from the barrel section  41  of the socket. In one embodiment of the invention, the inside diameter of the sockets is such to allow 0.010 inch off axis in any radial direction in the back of the contact. Copper contacts can be plated to prevent corrosion and maintain electrical performance. 
         [0043]      FIG. 4B  is a perspective view of the socket shown in  FIG. 4A . A retention spring  46  may be added to the distal ends of the tynes in the retention section  43  between the distal flange  44  and the proximal flange  45 . The retention spring  46  encircles all of the tynes in the tyne section  42  and forces the tynes to bend or flex in radially transverse inward directions toward each other to reduce the size of the opening  47 . By selecting a retention spring  46  that has a desired resilience, the socket may be engineered to apply a selected mating force with a male contact pin of an aircraft fixed connector (receptacle). A relatively stronger retention spring  46  will apply relatively stronger mating forces. In alternative embodiments, a plurality of retention springs  46  may be applied to a single socket. For example, four relatively smaller retention springs may be used to apply the same mating force as a single relatively larger retention spring. Sockets comprising a single retention spring may be cheaper to manufacture because it may take longer to apply multiple springs. 
         [0044]    Different embodiments of the invention may have sockets that have different numbers of tynes. For example, each socket may have any number of tynes, for example, between two and ten tynes. 
         [0045]      FIG. 4C  is a perspective side view of the socket shown in  FIGS. 4A and 4B . As previously noted, each socket comprises an annular pivot flange  37 . The annular pivot flange  37  comprises a chamfer pivot surface  38 . The chamfer pivot surface  38  enables the socket to engage the internal block  20  and pivot relative to annular beveled pivot surface  28  (see  FIG. 3 ). From the view shown in  FIG. 4C , the chamfer or rounded corner of the chamfer pivot surface  38  is more readily visible. 
         [0046]    Referring to  FIG. 5A , a perspective view of a plug body  10  is illustrated. The plug body  10  may be a unitary molded synthetic rubber structure for housing the internal block  20  and the socket group  30 , not shown. At a front face  11  of the plug body  10 , openings  12  are provided to give access to each of the sockets  31  through  36  when the socket group and internal block  20  are assembled inside the plug body  10 . The exterior of the plug body  10  is configured in size and shape so as to mate with an aircraft fixed connector (receptacle) as is standard in the industry.  FIG. 5B  is a perspective view of a horizontal cross-sectional of the plug body  10  shown in  FIG. 5A . In this view, a void space is revealed to show where the internal block  20 , not shown, is to be positioned within the plug body  10 .  FIG. 5C  is a perspective view of a vertical cross-sectional view taken along a vertical plain to the middle of the plug body  10 . This figure shows the plug body as illustrated in  FIGS. 5A and 5B . This cross-sectional view also shows the internal void space where the internal block  20  in socket group  30  is to be positioned within the plug body  10 . 
         [0047]    According to one aspect of the invention, the plug body  10  may be molded over the internal block  20  and socket group  30 . The plug body may be comprised of a number of chlorosulfonated polyethylene rubber, or synthetic rubber, EPDM, CSM, or similar synthetic rubber or plastic material. As shown in  FIG. 6A , the plug body  10  may be molded by first securing the socket group  30  and the internal block  20  to an arbor  50 . The arbor  50  has an equal number of nipples as there are contacts (six are shown)  51  that extend through the holes in the face section of the internal block  10  and into the openings  47  of the sockets in the socket group  30 . These nipples are appropriately sized to interface with the different sized contacts. These nipples  51  serve to properly position the internal block  20  and socket group  30  relative to the arbor  50 . The nipples provide a socket-to-socket spacing as preferentially required by the mating receptacle (1.000 inch is shown in this embodiment). The socket contacts of the socket group  30  may be loaded from the back of the internal block  20  and pulled into and against the internal block  20  with 8-32 screws  52  introduced from the front of the arbor  50 . Common COTS screws  52  extend through the arbor  50  and thread into the barrel sections of sockets of the socket group  30 . As the COTS screws  52  are threaded into the sockets, the sockets and the internal block  20  are pulled toward the arbor  50  until the nipples  51  are fully engaged in the sockets. A plug body  10  may then be molded over the internal block  20  and socket group  30 . The thickness of the molded plug body  10  over the front of the face section may be at least about 0.100 inches so that no part of any socket, nor any part which is electrically connected to any socket may be within about 0.100 inches of the front end of the plug. This thickness could vary with other connector configurations Because the arbor holds the contacts in position, the molded plug can be immediately removed from the mold after curing. 
         [0048]    As shown in  FIGS. 6A and 6B , the molded plug body completely encloses the internal block  20  and the socket group  30 , except that the nipples  51  preclude any mold material from flowing into the cavities of the internal block  20 . The rubber of the plug body completely encircles the exposed surfaces of the annular pivot flange  37  (see  FIGS. 4A through 4C ) to securely hold the sockets of the socket group  30  in the internal block  20 . In particular, the molded plug body  10  secures the sockets so that the chamfer pivot surfaces  38  of the sockets  30  maintain contact with the annular bevel pivot surfaces  28  of the internal block  20 . The material comprising the plug body  10  may be sufficiently flexible to allow small local elastic deformations around the annular pivot flanges  37  to allow the sockets to align with pins during engagement/disengagement. 
         [0049]    In one embodiment of the invention, the ground power connector (plug) may have power sockets measuring 22 pounds contact force each and relay sockets measuring 2 pounds contact force each. The sum of the 4 power socket contact forces and the 2 relay socket contact forces may then be about 92 pounds. The sum of the individual socket contact forces may be close to the plug/receptacle force. This is a result of eliminating binding forces due to out of position sockets found in traditional plugs. As a result, the mating and demating forces can be accurately predicted simply by summing the individual contact forces. 
         [0050]    The force required to mate the plug with its applicable receptacle may be as high as about 50 pounds for three-socket plugs and 100 pounds for six-socket plugs. The force required to remove the plug from the receptacle at each point in the first half-inch of travel from the fully engaged position may be about 30-50 pounds for three-socket plugs, and may be about 80 to 120 pounds for six-socket plugs. The force required to engage a female socket with a male pin contact may be up to about 24 pounds for the A, B, C and N contacts and up to about 2 pounds for the E and F contacts. The force required to remove a female socket from a male pin contact may be between about 16 to 24 pounds for the A, B, C and N contacts and about 2 pounds for the E and F contacts. The force measurements may be made using a tension/compression tester equipped with a means for measuring or recording lineal displacement versus force. The rate of movement may be about 7-9 inches per minute. 
         [0051]    According to one aspect of the invention, the internal block may be a different color than the plug body so that when the plug body becomes worn, the internal block may be more clearly visible where the plug body is abraded away. By being different colors, the ground power connector (plug) may provide a visual indication when the connector is worn out and ready for replacement or refurbishment. 
         [0052]    Although the inventions are described with reference to preferred embodiments, it should be appreciated by those skilled in the art that various modifications are well within the scope of the invention. From the foregoing, it will be appreciated that an embodiment of the present invention overcomes the limitations of the prior art. Those skilled in the art will appreciate that the present invention is not limited to any specifically discussed application and that the embodiments described herein are illustrative and not restrictive. From the description of the exemplary embodiments, equivalents of the elements shown therein will suggest themselves to those skilled in the art, and ways of constructing other embodiments of the present invention will suggest themselves to practitioners of the art. Therefore, the scope of the present invention is not limited herein. 
         [0053]    Although the disclosed embodiments are described in detail in the present disclosure, it should be understood that various changes, substitutions and alterations can be made to the embodiments without departing from their spirit and scope.