Abstract:
An electrical connector comprising a housing and electrical contacts connected to the housing. The electrical contacts comprise paired signal and ground contacts, and additional ground contacts. The additional ground contacts are arranged relative to the paired contacts to divide the paired contacts into subdivisions of equal numbers of the paired contacts. The subdivisions and the additional ground contacts are arranged to allow for multiple relative orientation connections of a mating connector.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical connectors and, more particularly, to an electrical connector having center ground contacts. 
     2. Brief Description of Earlier Developments 
     U.S. Pat. Nos. 5,429,520 and 5,433,617 disclose electrical connectors having a ground contact plate unit with a general cross shape and a cross-shaped receiving area in a mating electrical connector establishing four quadrants of contacts. It is also known in the connector art for two contacts in an electrical connector to transmit the same signal (but in opposite voltage), such as for high speed signals, wherein the differences between the parallel signals can be compaired or combined with any differences (e.g. noise) being removed. These are generally known as a “differential pair” of contacts. A “single ended” contact generally refers to a single signal contact surrounded by a ground (e.g. a coaxial conductor or pseudo-coaxial arrangement). It is desired to provide electrical connectors with contacts arranged in a symmetrical mating pattern which allows a first connector to be mated with a second connector in various orientations, such as 90° apart. A problem exists with conventional electrical connectors in that they do not allow common electrical connector parts to be used in the manufacture of both an electrical connector with only single ended signal contacts and an electrical connector with both differential pair contacts and single ended contacts. It is also desired to provide differential pair and single ended contact arrangements which can use common manufacturing parts as used to manufacture the electrical connectors having only single ended contacts. A problem exists with conventional electrical connectors in that they do not allow differential pair and single ended contact arrangements to be configurable into different patterns. It is also desired to allow differential pair and single ended contact arrangements to be configurable into different patterns. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, an electrical connector is provided comprising a housing and electrical contacts connected to the housing. The electrical contacts comprise paired signal and ground contacts, and additional ground contacts. The additional ground contacts are arranged relative to the paired contacts to divide the paired contacts into subdivisions of equal numbers of the paired contacts. The subdivisions and the additional ground contacts are arranged to allow for multiple relative orientation connections of a mating connector. 
     In accordance with another embodiment of the present invention, an electrical connector is provided comprising subassembly wafers and a ground plane member. At least two of the wafers comprise a housing, paired signal and ground contacts, and an additional ground contact in a general center of a connection area for the paired contacts. The ground plane member is located between at least two of the wafers. The ground plane member has contact areas located between at least some of the paired contacts of one of the at least two wafers and at least some of the paired contacts of the other one of the at least two wafers. 
     In accordance with another embodiment of the present invention, an electrical connector is provided comprising paired signal and ground contacts; additional ground contacts located between at least some of the paired contacts; and a housing having first contact receiving areas with the paired contacts located therein and second contact receiving areas with the additional ground contacts located therein. At least one of the second contact receiving areas does not contain an additional ground contact such that two of the paired contacts on opposite sides of the at least one second contact receiving area form a differential pair of contacts for high speed differential pair signal transmission. 
     In accordance with one method of the present invention, a method of manufacturing an electrical connector is provided comprising steps of providing a housing having first contact receiving areas and second contact receiving areas; positioning paired signal and ground contacts in the first contact receiving areas; and positioning additional ground contacts in the second contact receiving areas. At least one of the second contact receiving areas does not have an additional ground contact located therein such that two of the paired contacts on, opposite sides of the at least one second contact receiving area form a differential pair of high speed signal transmission contacts. 
     In accordance with another embodiment of the present invention, an electrical connector is provided comprising a first subcomponent wafer assembly comprising a first housing and single ended signal and respectively paired ground contacts connected to the first housing; and a second subcomponent wafer assembly connected to the first subcomponent wafer assembly. The second subcomponent wafer assembly comprises a second housing and, connected to the second housing, pairs of differential pair signal contacts and respectively associated ground contacts for each signal contact. 
     In accordance with another method of the present invention, a method of manufacturing electrical connectors having both single ended signal contacts and differential pair signal contacts is provided comprising steps of providing pairs of signal contacts and respective ground contacts; and selectively locating additional ground contacts between at least two first ones of the pairs. At least two second ones of the pairs do not have the additional ground contacts therebetween such that the signal contacts of the two second pairs form a differential pair of high speed signal transmission signal contacts and signal contacts of the two first pairs form single ended signal transmission signal contacts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of an electrical connector incorporating features of the present invention; 
     FIG. 1A is a perspective view of a portion of the connector shown in FIG. 1; 
     FIG. 2 is an exploded perspective view of one of the contact module assemblies shown in FIG. 1; 
     FIG. 3 is a front elevational view of the connector shown in FIG. 1 with the front housing part and certain signal contacts removed; 
     FIG. 4 is a front elevational view of a mating electrical connector for use with the connector shown in FIG. 1; 
     FIG. 5 is a front elevational view similar to FIG. 3 of an alternate embodiment of the present invention; 
     FIG. 6 is a front elevational view of a mating electrical connector for use with the connector shown in FIG. 5; 
     FIG. 7 is a front elevational view similar to FIG. 3 of another alternate embodiment of the present invention; 
     FIG. 8 is a front elevational view of a mating connector for use with the connector shown in FIG. 7; 
     FIGS. 9-12 are front elevational views of alternate embodiments of mating header connectors for use with appropriately configured alternate embodiment receptacle connectors; 
     FIG. 13 is a schematic diagram of a signal contact layout for another alternate embodiment of a mating header connector; and 
     FIG. 14 is a schematic view of a contact module layout for another alternate embodiment of a receptacle connector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a perspective view of an electrical connector  10  incorporating features of the present invention. Although the present invention will be described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. 
     The connector  10  in this embodiment is a receptacle electrical connector adapted to be connected to a first electrical component (not shown) such as a printed circuit board and removably connectable to a mating electrical connector, such as a pin header (see FIG.  4 ). The connector  10  and connection system is similar to that described in U.S. provisional patent application No.: 60/117,957 filed Jan. 28, 1999 which is hereby incorporated by reference in its entirety. The connector  10  generally comprises a housing  12  and modules or subassembly wafers  14 . However, in alternate embodiments more or less components can be provided. The housing  12  generally comprises a rear housing member  16  and a front housing member  18 . 
     Referring also to FIG. 1A, rear housing member  16  is generally an open structure formed by sidewalls  35 ,  37 ; a rear wall  39 ; and a top wall  41 . The open interior of rear housing member  16  receives the rear portions of a series of the modules  14  arranged side-by-side. Specifically a groove  71   b  receives a spline  71   a  to ensure proper alignment. Receptacle  10  accurately rests on a daughterboard (not shown) using alignment posts  43  extending downwardly from sidewalls  35 ,  37 . Alignment posts  43  engage corresponding through holes in the daughterboard preferably by an interference fit. 
     Front housing member  18  is also generally an open structure formed by a mating face  45 ; sidewalls  47 ,  49 ; bottom wall  51 ; and top wall  53 . The open interior of The front housing member  18  receives the front portions of the series of modules  14  arranged side-by-side. As with housing  16 , housing  18  can have grooves (not shown) to receive another spline  71   a  on wafer  30 . Front housing member  18  secures to rear housing member  16  using latch structures  55 ,  57  on each housing, respectively. The front housing member  18  secures to the rear housing member  16  after placement of the modules  14  within the rear housing member  16 . Once assembled, receptacle  10  can mount to the daughterboard. 
     The mating face  45  of the front housing member  18  includes an array of lead-ins  59 . Lead-ins  59  accept corresponding signal pins and ground pins from the header (See FIG.  4 ). Once the header mates with the receptacle  10 , the signal and ground contacts of receptacle  10  engage the signal pins and ground pins of the header. This feature will be described in more detail below. 
     As seen in FIG. 1A, the connector  10  can include a ground plane member  20 . The ground plane member  20  is a one-piece member comprised of electrically conductive material which is also ferromagnetic. In alternate embodiments the ground plane member  20  could be comprised of multiple members. In this embodiment the ground plane member  20  comprises first connection ends  22  and second connection ends  24 . The first connection ends  22  comprise through-hole solder trails, but any suitable second connection ends could be provided. The second connection ends  24  comprise opposing spring contact arms forming a pin receiving area therebetween, but any suitable second connection ends could be provided. The ground plane member  20  has break-off sections  26  between the second connection ends  24  and the main body  28 . The break-off sections can be severed or cut during manufacturing to remove one or more of the second connection ends  24  to customize or configure the ground place member as further understood below. However, in an alternate embodiment the break-off section needs not be provided or any suitable type of severing system could be provided. 
     Referring also to FIG. 2 an exploded perspective view of one of the modules  14  is shown. Each module  14  generally comprises a frame or wafer  30 , signal contacts  32  and ground contacts  34 . However, in alternate embodiments, more components could be provided, and/or the component need not be provided as uniform modules. Wafer  30  can be a block of insulative material. The wafer  30  can be formed from several pieces  30   a ,  30   b . Alternatively, however, wafer  30  could be formed unitarily from one piece (not shown). In this embodiment the module  14  comprises six signal contacts and seven ground contacts, but any suitable number of contacts could be provided. The center ground contact  34   a  may also be omitted as further understood below. A first major surface  67  of wafer piece  30   a  has a series of channels, grooves or apertures  68  in which ground contacts  34  reside. When arranging modules  14  side-by-side, first major surface  67  of a first module  14  can abut a second major surface  69  of a second adjacent module. In order to place modules  14  side-by-side, second major surface  69  can be generally featureless. The top surface of wafer piece  30   a  includes a projection  71 . As seen in FIG. 1, projections  71  can abut the front edged of rear housing member  16  during, and after, assembly. The interaction between projections  71  and the front edge of rear housing member  16  helps align modules  14  within rear housing member  16 . The wafer piece  30   a  can also have a spine  71   a  . The spine  71   a  can be located in a groove  71   b  in the rear housing piece  16 . Signal contacts  32  include a mounting end  73  for securing to the daughterboard, a mating end  75  for interacting with signal pins of the header, and an intermediate portion  77 . The mounting ends  73  can have press-fit solder tails that engage plated through holes in the daughterboard. However, other types of terminations for mounting ends  73  could be used. Typically, an overmolding process embeds signal contact  32  in wafer piece  30   a  (or wafer  30  if one piece), however, other techniques could be used. The second wafer piece  30   b  is preferably premolded and subsequently mounted over the mating ends  75  of the signal contacts  32 . The second wafer piece  30   b  includes first receiving apertures  40  and second receiving apertures  42 . The first receiving apertures  40  receive the mating ends  75  of the signal contacts  32 . The second receiving apertures  42  receive the mating ends of the ground contacts  34 . The center second receiving aperture  42   a  extends into an opposite side of the second wafer piece  30   b  than the other second receiving apertures  42 , but this need not be provided. Also in this embodiment, the receiving apertures  40 ,  42  above the center second receiving aperture  42   a  are preferably mirror images of the receiving apertures  40 , 42  below the center second receiving aperture  42   a . However, this need not be provided. 
     The mating end of the signal contacts  32  can have a dual beam contact configuration to engage signal pins of the header. The beams  79 ,  81  of the dual beam contact are arranged generally perpendicular to each other. In this arrangement, the bifurcation engages adjacent surfaces of the mating signal pins. Beams  79 ,  81  deflect upon insertion of the mating signal pins. The movement of signal pins along the beams  79 ,  81  during insertion provides good wiping action. In addition, the force imparted to the signal pins by deflection of the beams  79 ,  81  provides good contact pressure or contact normal force. 
     As with signal contacts  32  the ground contacts  34  include a mounting end  83  for securing to the daughterboard, a mating end  85  for interacting with ground pins of the mating header, and an intermediate portion  87 . Mounting ends  83  can have press-fit solder tails that engage plated through holes in the daughterboard. However, other types of terminations for mounting ends  83  could be used. Mating end  85  uses a dual beam-type contact arrangement to engage ground pins of the header. Mating end  85  includes a first beam  89  arranged generally perpendicular to a second beam  91 . A minor surface of first beam  89  supports the ground pin. As discussed above, the beam  89  provides good contact force and wipe. Second beam  91  is bifurcated into a stationary section  93  and movable section  95 . Upon engagement of movable section  95  of second beam  91  with a ground pin, movable section  95  deflects. As with the other contacts, the deflection provides good contact force and wipe. 
     Signal contacts  32  within module  14 , as with ground contacts  34  within module  14 , preferably do not maintain the same orientation throughout the module  14 . Furthermore, signal contacts  32  and ground contacts  34  in one module  14  preferably do not exhibit the same orientation as signal contacts  32  and ground contacts  34  in all of the other modules  14 . 
     Referring also to FIG. 3, a front elevational view of the connector  10  is shown with the front housing member  18  removed. In this embodiment the connector  10  comprises six of the modules  14 . In alternate embodiments more or less than six modules could be used. In this embodiment the six modules  14  actually comprise two types of modules  14   a ,  14   b  which are mirror images of each other. In alternate embodiments more or less than two types of modules could be provided and, the modules need not be mirror images of each other. 
     The general L shape of the signal contacts  32  generally correspond to the positions of the beams  79 ,  81 . Likewise, the general L shape of the ground contacts  34  generally correspond to the positions of the beams  89 ,  91 . Two areas L 1 , L 2 , preferably passing through a center of the receptacle  10 , define four quadrants Q 1 , Q 2 , Q 3 , Q 4 . Each signal contact  32  corresponds to a ground contact  34  to form a contact pair. In the arrangement shown in FIG. 3, the signal contact  32  and ground contact  34  in each contact pair have the same orientation. In other words, signal contact  32  and ground contact  34  of contact pair face the same direction. Generally speaking, the orientation of each contact pair within a quadrant (even in a different module) remains the same. However, the orientation of contact pairs in other quadrants differ from the orientation of contact pairs in other quadrants (even on the same module). Typically, contact pairs in one quadrant are rotated 90° relative to contact pairs in an adjacent quadrant. For example, a contact pair in quadrant Q 1  is rotated 90° relative to a contact pair in quadrant Q 2 . 
     Since one module  14  can have contacts  32 ,  34  residing in more than one quadrant, the orientation of some contacts  32 ,  34  in each module  14  can differ from the orientation of other contacts in the same module. Typically, contact pairs in a module  14  that reside in one quadrant are preferably mirror images of the contact pairs in the same module that reside in the other quadrant. For example, module  14   a  in FIG. 3 has contact pairs in quadrants Q 1  and Q 4 . Contact pairs in module  14   a  that are in quadrant Q 1  are mirror images of the contact pairs in quadrant Q 4 . Other arrangements are also possible. In an appropriate situation, the contact in one quadrant could be rotated 90° to the contacts in the adjacent quadrant. 
     Area L 1  is generally occupied by the ground plane member  20  for single ended applications. Thus, the ground plane member  20  forms a ground and a shield through the center of the connector  10  between the signal contacts  32  in the two modules  14   a ,  14   b  closest to the ground plane member. For example, the top second connection end  24   a  is located between the mating ends  75   a ,  75   a  of the two top signal contacts  32  on opposite sides of the ground plane member. Area L 2  is generally occupied by the module ground contacts  34   a  for single ended applications. Thus, the module ground contacts  34   a  form both grounds and shields in a path generally through the center of the connector  10  between the signal contacts in each respective module  14  closets to the module ground contact  34   a . For example, the mating ends  75   b ,  75   b  of the two middle signal contacts  32  on opposite sides of each module ground contact  34   a  and their intermediate portions  77  (see FIG. 2 will have the module ground contacts  34   a  therebetween. With this arrangement the ground contacts  34   a  and ground plane member  20  form a general cross-shaped ground and shield between the four quadrants Q 1 , Q 2 , Q 3 , Q 4 , but which still allows for 90° offset connection possibilities with the mating electrical connector pin header. Ground plane  20 , ground contacts  34   a  and ground contacts  34  form a pseudo-coaxial structure around each signal contact  32 . Clearly, therefore, the signal contacts  32  are preferably single ended signal contacts. 
     FIG. 4 is a front elevational view of a mating electrical connector or header  100  adapted to be connected to the receptacle connector  10 . In particular, the connector  100  is a pin header connector which is fixedly connectable to an electrical component, such as a printed circuit board. The connector  100  includes a housing  102 , ground contacts  104 , associated signal contacts  106 , and ground shields  108 . The housing  102  includes a receiving area  110  for receiving the mating face  45  of the receptacle connector  10 . The ground contacts  104  have male pin sections  112 . The signal contacts  106  have male pin sections  114 . When the two connectors  10 , 100  are properly connected to each other, the pin section  112 ,  114  extend into the lead-ins  59  and make electrical contact with the ground contacts  34  and signal contacts  32 , respectively. The mating connector  100  may also comprise additional ground contacts  104   a . The additional ground contacts  104   a  do not have associated or paired respective signal contacts as the other ground contacts  104  but help create a pseudo-coaxial structure. In this embodiment the additional ground contacts  104   a  are arranged in a general cross-shaped pattern as illustrated by area L 3 . The male pin sections of the additional ground contacts  104   a  are adapted to make electrical contact with the ground contacts  34   a  in area L 2  and ground plane member  20  in area L 1  shown in FIG.  3 . In alternate embodiments other types of suitable mating connection and/or contacts could be provided. 
     Referring now also to FIG. 5 an alternate embodiment of the present invention will be described. FIG. 5, similar to FIG. 3, shows the receptacle connector  10 ′ with its front housing member removed. In this embodiment the connector  10 ′ is substantially identical to the connector  10 , but does not include the ground plane member  20 . Thus, a shield is not provided between the signal contacts  32  in the two modules  14   a ,  14   b  closest to each other at the center of the connector  10 ′. Area A is empty, allowing signal contacts  32  in modules  14   a,b  to be driven as differential pairs. With this embodiment the connector  10 ′ can comprise both single ended signal contacts  32   S  as well as differential pair signal contacts  32 D. More specifically, area B 1  forms six differential pair signal contacts; each pair comprising one signal contact from each of the two closest modules  14   a ,  14   b . The rest of the signal contacts (located outside area B 1 ) can remain single ended signal contacts because of the shielding provided by the ground contacts  34 ,  34   a . The ground contacts  34 ,  34   a  in area B 1  also prevent signal interference between adjacent pairs of the differential pair signal contacts  32   D  and also between the differential pairs  32   D  and the single ended contacts  32   s . FIG. 6 shows a mating connector  100 ′ similar to the mating connector  100  shown in FIG. 4 for use with the connector  10 ′. As can be seen, the center column of additional ground contacts has been omitted. Thus, area B 2  is formed which can use the six pairs of signal contacts  114   D  as differential pair signal contacts. The remaining signal contacts  114   S outside area B 2  can be used as single ended signal contacts because of the ground shields  108  and ground contacts  104 ,  104   a . In an alternate embodiment a ground plane member similar to member  20  could be located in area A, but have all of its second connection ends  24  removed. 
     Referring now also to FIG. 7, another alternate embodiment will be described. In this embodiment the receptacle connector  10 ″ is substantially the same as the receptacle connector  10 ′ shown in FIG. 5 except that the connector  10 ″ has all the center ground contacts  34   a  omitted. Thus, area C 1  is formed which comprises ten differential pair signal contacts  114   D . Area C 1  has a general cross-shape, but any suitable shape could be provided depending upon which ones of the center ground contacts  34   a  and/or second connection ends  24  are omitted. The signal contacts  114   5  outside area C 1  can be used as single ended signal contacts because of the shielding provided by the ground contacts  34 . Referring also to FIG. 8 a mating connector  100 ″ is shown similar to the mating connector  100 ′ shown in FIG. 6 for use with the connector  10 ″. As can be seen, both the center column and center row of additional ground contacts have been omitted. Thus, area C 2  is formed which can use the ten pairs of signal contacts. The remaining signal contacts  114 D (i.e. those not used as differential pair signal contacts) outside area C 2  can be used as single ended signal contacts  114 s because of the ground shields  108  and ground contacts  104 . 
     FIGS. 9-12 show other alternate embodiments of the mating connectors, it being understood that their respective receptacle connectors would be correspondingly configured to mate similar to the connectors  10  and  100 ,  10 ′ and  100 ′, and  10 ″ and  100 ″. The receptacle connectors would have the appropriate second connection ends  24  of the ground plane member  20  removed and/or the appropriate center ground members  34   a  omitted corresponding to the empty apertures  29  in the housing of the mating connector. In the embodiment shown in FIG. 9, the mating connector  200  is similar to the mating connector  10  shown in FIG. 4, but has four empty apertures  29 . This forms an area D 2  having differential pair signal contacts  114   D . The contacts  114   S  outside the area D 2  can be used as single ended signal contacts due to the shielding provided by ground shields  108  and ground contacts  104 ,  104   a.    
     In the embodiment shown in FIG. 10, the mating connector  202  is similar to the mating connector  10  shown in FIG. 4, but has eight empty apertures  29 . This forms an area E 2  having differential pair signal contacts  114   D . The contacts  114   S  outside the area E 2  can be used as single ended signal contacts due to the shielding provided by ground shields  108  and ground contacts  104 ,  104   a.    
     In the embodiment shown in FIG. 11, the mating connector  204  is similar to the mating connector  10  shown in FIG. 4, but has nine empty apertures  29 . This forms an area F 2  with a general “T” Shape having differential pair signal contacts  114   D . The contacts  114   S  outside the area F 2  can be used as single ended signal contacts due to the shielding provided by ground shields  108  and ground contacts  104 ,  104   a . This embodiment also illustrates that the patterns for the differential pair signal contacts and single ended signal contacts can be asymmetric. In such an asymmetric arrangement, the mating connectors should mate in only one orientation. 
     In the embodiment shown in FIG. 12, the mating connector  206  is similar to the mating connector  10  shown in FIG. 4, but has four empty apertures  29  provided as two spaced apart groups. This forms two areas G 2   a , G 2   b  having differential pair signal contacts  114   D . The contacts  114   S  outside the areas G 2   a , G 2   b  can be used as single ended signal contacts due to the shielding provided by ground shields  108  and ground contacts  104 ,  104   a . This embodiment illustrates that the differential pair contacts can be provided as more than one group or area (perhaps spaced from each other) and do not need to pass through the center of the connector. 
     Referring now to FIG. 13, a schematic diagram of a signal contact layout for another alternate embodiment is shown. In this embodiment the connector  208  includes an array of 8×8 signal contacts. However, any suitable number or array shape and size could be provided. The ground contact layout and ground shields are not shown merely for the sake of clarity. This arrangement is achieved by allowing the placement of ground plane  20  at locations other than a central position. In this embodiment the connector  208  includes three groups (H 2   a , H 2   b , H 2   c ) which are separated by two groups of single ended signal contacts  114   s . In other words, ground planes are place between: ( 1 ) group H 2   a  and the row of single ended contacts,  114   s ; ( 2 ) the row of single ended contacts  114   s  and group H 2   b . This pattern continues across the connector. In alternate embodiments the layout or pattern for the signal contacts could be varied such as not having any signal ended signal contacts, having only one group of single ended signal contacts, having more than three groups of differential pair signal contacts (spaced from each other and/or not spaced from each other), and having symmetric and/or non-symmetric patterns. 
     Referring now to FIG. 14, a schematic illustration of another alternate embodiment of the receptacle connector is shown. In this embodiment the connector  210  comprises five modules or wafer subassemblies  14   a ,  14   b  and  14   c . The modules form a 6×6 array of paired signal and ground contracts  32 ,  34  as well as additional ground contacts  34   a . However, in this embodiment the connector only has two left-hand modules  14   a  and two right hand modules  14   b . The left and right hand modules  14   a ,  14   b  each comprise a 1×6 array of only single ended signal contacts  32   s . In an alternate embodiment the left and right hand modules  14   a ,  14   b  could also form differential pair signal contacts. The center module  14   c  comprises a 2×6 array of associated signal and ground contacts in a common wafer housing  30 ′ forming six differential pair signal contacts  32 D. Thus, the single module  14   c  comprises differential pair signal contacts in a common housing. In an alternate embodiment the center module  14   c  could include single ended signal contacts, such as when the housing  30 ′ is adapted to receive a ground plane member. 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.