Abstract:
A connector system for mechanically connecting two structural elements to each other, consisting of a connector element and mating grooves in each structural element. The connector element is comprised of a base plate having a split-tongue element at each side or end of said base plate. Each joined element has a mating groove formed into its connector-receiving surface. The mating groove is designed to allow fabrication via four sequential circular saw cuts, without loss of saleable decorative surface, and at a rate consistent with economical commercial production of vinyl, laminate, or hardwood flooring. The connector element is readily extruded in a variety of polymers, including PVC. The connector and mating grooves interact so as to generate a force component acting to forcibly draw the connector into the mating grooves. The connector system operation is relatively insensitive to geometric deviations associated with normal manufacturing methods.

Description:
CROSS-REFERENCE 
       [0001]    This is a continuation-in-part application to the U.S. application Ser. No. 13/086,424, filed on Apr. 14, 2011, from which priority is claimed, and entirety of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    This invention relates to a connector system for mechanically joining building panels (such as vinyl, laminate, or hardwood flooring); mechanically attaching decorative items (such as wall panels, ceiling panels, or automotive trim); mechanically attaching subsystems (such as automotive dashboards); or mechanically connecting elements of ready-to-assemble furniture. 
         [0004]    2. Description of Related Art 
         [0005]      FIG. 1  is a schematic drawing of the ubiquitous tongue and groove joining system typically used to join structural elements such as hardwood flooring. In the figure, hardwood flooring substrate element  1  with decorative surface  2  is to be connected to hardwood flooring substrate element  3  with decorative surface  4 . A solid tongue  5  is machined from the solid substrate material with the resultant loss of saleable decorative surface  6 . A mating groove  7  is formed in substrate element  3  to accept tongue  5 . The structural elements are joined by moving element  3  in the direction of the arrow so as to cause mating groove  7  to receive tongue  5 . The tongue is normally forcibly received into its mating groove and once received, the tongue, though held in place by friction, is not actively drawn into the groove 
         [0006]    Additional prior art is found in U.S. patent application Ser. No. 12/705,593, EFS ID 7006498 of Baker and Vitale which discloses a method for “Laying and Mechanically Joining Building Panels or Construction Elements”. The mating groove described in this patent application is shown in  FIG. 2 . The Baker/Vitale patent application describes a system that is similar to that of the present patent application but differs in the following two significant ways:
       1. The locking steps located at the distal end of the Baker/Vitale mating groove can only be fabricated using a device such as a rotary router cutter or a linear broach cutter, neither of which are consistent with high speed commercial flooring production.   2. The connector and mating groove interaction in the Baker/Vitale system is more sensitive to geometric deviations arising from manufacturing tolerances.       
 
         [0009]    The differences noted above are a consequence of the mating groove geometry associated with the Baker/Vitale patent application. As seen in  FIG. 2 , the mating groove  27  has steps  8  and  9  near its distal end. These steps are intended to interact with a catches on a mating split-tongue connector in such a manner as to forcibly draw the connector into the groove. 
         [0010]    As show in  FIG. 2 , a hold region extension line  10  drawn parallel to face  8  does not exit the groove through the groove entrance region  11  but rather intersects the opposite sidewall of the groove at  12 . Consequently, steps  8  and  9  must be formed using a either a rotary router cutting tool  13  as shown in  FIG. 3A , or a linear broach cutting tool  14 , as shown in  FIG. 3B . As seen in  FIG. 3A , the diameter  16  of the router cutting tool is limited to the maximum distance  15  between the outer surfaces of the steps. That is, in contradistinction to the connector system disclosed in this application, the diameter of the rotary cutting tool cannot be made larger than the maximum groove width. 
         [0011]    Due to the limited rotary cutter diameter shown in  FIG. 3A , the rotary approach is precluded, by tool heating and chip removal considerations, from forming a mating groove at the speeds (i.e., approximately 360 linear feet per minute) consistent with economical production of the thousands of linear feet of groove typically required in commercial vinyl, laminate, or hardwood flooring. The broach approach to groove fabrication shown in  FIG. 3B , faces similar heating and chip removal obstacles relative to the same commercial application. 
         [0012]    It should be noted, however, that although the rotary router approach is precluded, by economics, from use in high-speed flooring production; it can be used in other commercial applications, such as ready-to-assemble (RTA) furniture, where groove linear dimensions are only 2″ to 3″ and low-speed groove fabrication is economically viable. 
       SUMMARY OF INVENTION 
       [0013]    The objective of the present invention is to provide a versatile, robust, low cost connector system, suitable for the mechanical joining of two construction elements; having a mating groove geometry that can be formed at a rate required for economical production of vinyl, laminate, or hardwood flooring; and that is also suitable for a wide variety of other less demanding applications, e.g., ready-to-assemble furniture. 
         [0014]    The invention comes in two preferred embodiments: a lateral embodiment and a normal embodiment. The advantage of the lateral embodiment relative to the normal embodiment is that, once assembled, the lateral embodiment is completely hidden from view; a feature that is very desirable for ready-to-assemble furniture. Conversely, the normal connector, though visible after assembly, is only visible from the under surface of flooring, its preferred application, and hence, is totally hidden from view by the upper decorative flooring surface. In addition, in a completed floor installation, the normal connector allows the removal of a damaged floor board without damage or intrusion into the floor boards adjoining it. This is because in flooring the direction of board removal must be normal to the flooring surface. Fortunately, in the normal embodiment, this direction is the same as the direction of tongue insertion and retraction, allowing the board to be removed from the tongue without damage to either the tongue, the board groove, or the adjoining boards. This feature has been nicely demonstrated in vinyl flooring hardware. 
         [0015]    In ready-to-assemble furniture, unlike flooring, the direction of structural component removal is not restricted to a direction normal to the component decorative surface. Consequently, in ready-to-assemble furniture, the preferred application of the lateral connector; the structural component can almost always be removed from the connector element in a direction parallel to that of tongue insertion and retraction, and hence without damage to the connector tongue or the joined components. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which similar element are given similar reference numerals. 
           [0017]      FIG. 1  is a side view of a typical solid tongue and groove connection system 
           [0018]      FIG. 2  is a side view of the groove disclosed by Baker and Vitale in U.S. patent application Ser. No. 12/705,593, EFS ID 7006498 
           [0019]      FIG. 3A  shows the groove in  FIG. 2  being formed using a rotary router cutting tool. 
           [0020]      FIG. 3B  shows the groove in  FIG. 2  being formed using a linear broach cutting tool. 
           [0021]      FIG. 4  is a lateral split-tongue connector system used to mechanically join two hardwood floor boards. 
           [0022]      FIG. 5  is a normal split-tongue connector system used to mechanically join two hardwood floor boards. 
           [0023]      FIG. 6  show the mating groove for a normal connector. 
           [0024]      FIG. 7  shows the mating groove for a lateral connector. 
           [0025]      FIG. 8  shows the manner in which the mating groove for a normal connector can be formed by four circular saw cuts. 
           [0026]      FIG. 9  shows a lateral split-tongue connector at three significant locations during installation into its mating groove: at the beginning of installation with no arm deflection; with the flexible arm nubs at the groove apex with maximum arm deflection; and with the split-tongue fully inserted with residual arm deflection. 
           [0027]      FIG. 10  shows a normal split-tongue connector at two significant locations during installation into its mating groove: with the flexible arm nubs at the groove apex with maximum arm deflection; and with split-tongue fully inserted with residual arm deflection. In each case a dashed outline shows the location of the split-tongue at the beginning of installation with zero arm deflection. 
           [0028]      FIG. 11  shows details of the geometric relationship between the split-tongue arms and the mating groove hold region when the split-tongue is fully inserted into its mating groove. 
           [0029]      FIG. 12  shows the force components acting on a split-tongue flexible arm nub due to the interaction of the nub with the groove entry region as a normal connector moves into its mating groove in the absence of friction. 
           [0030]      FIG. 13  shows the effect of friction between the split-tongue flexible arm nub and the mating groove entry region on the force components in  FIG. 12  when the split tongue is moving into its mating groove. 
           [0031]      FIG. 14  shows the force components acting on a split-tongue flexible arm nub due to the interaction of the nub with the groove hold region as a normal connector moves into its mating groove in the absence of friction. 
           [0032]      FIG. 15  shows the effect of friction between the split-tongue flexible arm nub and the mating groove hold region on the force components in  FIG. 14  when the split tongue is moving into its mating groove. 
           [0033]      FIG. 16  shows the force components acting on a split-tongue flexible arm nub due to the interaction of the nub with the groove hold region as a normal connector moves out of its mating groove in the absence of friction. 
           [0034]      FIG. 17  shows the effect of friction between the split-tongue flexible arm nub and the mating groove hold region on the force components in  FIG. 16  when the split tongue is moving out of its mating groove. 
           [0035]      FIG. 18  is a plot of the ratio of split-tongue force to arm displacement-force as a function of groove sidewall angle for different values of nub to ramp friction factor when the split-tongue is moving into or out of its mating groove. 
           [0036]      FIG. 19  shows an alternative connector and groove design. 
           [0037]      FIG. 20  shows the entry of the alternate connector into its mating groove. 
           [0038]      FIG. 21  shows the alternate connector at the condition of maximum arm deflection. 
           [0039]      FIG. 22  shows the alternate connector at its full insertion. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0040]    The connector system disclosed herein has two major preferred embodiments: a lateral connector system embodiment shown schematically in  FIG. 4  and a normal connector system embodiment shown schematically in  FIG. 5 . 
         [0041]    The following specification is divided into four sections. The first section, comprising  FIGS. 4 and 5  focuses on the structure and fabrication of the connector element of the preferred embodiments (item  17  in  FIG. 4  and item  31  in  FIG. 5 ). The second section focuses on the structure and fabrication of the connector mating groove of the preferred embodiments and comprises  FIGS. 6 ,  7 , and  8 . The third section focuses the manner in which the connector element and the mating groove of the preferred embodiments mechanically interact and comprises  FIGS. 9 to 18 . The fourth and last section focuses on an alternative connector and groove embodiment and comprises  FIGS. 19 to 22 . 
         [0042]      FIG. 4  shows the lateral embodiment of the connector system as used to connect hardwood flooring. The upper detail shows the connector system prior to assembly, and the lower detail shows the assembled system wherein the two floor board elements are mechanically joined by the connector. The arrows in the upper figure show the direction in which the joined elements move relative to the connector during assembly. The descriptor “lateral” in this embodiment indicates that the assembly motion is in a lateral direction, i.e., parallel to the flat upper surfaces of the floor boards and normal to the joined faces. 
         [0043]      FIG. 5  shows the normal embodiment of the connector system as used to connect hardwood flooring. The upper detail shows the connector system prior to assembly, and the lower detail shows the assembled system wherein the two floor board elements are mechanically joined by the connector. The arrows in the upper figure show the direction in which the joined elements move relative to the connector during assembly. The descriptor “normal” in this embodiment indicates that the motion of the connector relative the floor boards is normal to the flat upper surfaces of the boards. 
         [0044]    In  FIG. 4 , items  1  and  3  are left and right floor boards respectively, and items  2  and  4  are their respective decorative surfaces. Item  17  is a lateral connector element having left split-tongue element  18  and right split-tongue element  19 . The two split-tongues  18  and  19  are formed on either side of base plate  20 . The left split-tongue  18  has two flexible arms  21  and  22 , and right split-tongue  19  has two flexible arms  23  and  24 . The flexible arms  21 ,  22 ,  23 , and  24  have outward facing nubs  41 ,  42 ,  43 , and  44  respectively at their distal ends. Left split-tongue  18  mates with groove  25  in left floor board  1  and right split-tongue  19  mates with groove  26  in right floor board  3 . Said nubs  41  and  42  contact the side-walls of said mating groove  25  of said split-tongue  18 ; and said nubs  43  and  44  contact the side-walls of the said mating groove  26  of said split-tongue  19 . 
         [0045]    The split-tongues  18  and  19  in  FIG. 4  are similar to the solid tongue  5  in  FIG. 1  in the sense that each split-tongue and each solid tongue mate with one groove. That is, the solid tongue  5  mates with the groove  7  in  FIG. 1  and, similarly, the split-tongues  18  and  19  mate with the grooves  25  and  26  respectively in  FIG. 4 . The solid tongue in  FIG. 1 , however, differs from the split-tongues in  FIG. 4  in that the solid tongue in  FIG. 1  is a monolithic and relatively stiff structure, whereas the split-tongues in  FIG. 4  is comprised of at least two relatively flexible arms. 
         [0046]    In  FIG. 5 , items  1  and  3  are left and right floor board respectively, and items  2  and  4  are their respective decorative surfaces. Item  31  is a normal connector element having left split-tongue  33  and right split-tongue  36 . The two split-tongues  33  and  36  are supported on the left and right sides respectively of base plate  32 . The base plate  32  has a left extension  55  and a right extension  56 . The left split-tongue  33  has two flexible arms  34  and  35  respectively, and right split-tongue  36  has two flexible arms  37  and  38  respectively. The flexible arms  34 ,  35 ,  37 , and  38  have outward facing nubs  98 ,  99 ,  100 , and  101  respectively at their distal ends. The left split-tongue  33  mates with the mating groove  39  in the left floor board  1 , and the right split-tongue  36  mates with the mating groove  40  in the right floor board  3 . 
         [0047]    The mating groove design for the normal connector, item  31  in  FIG. 5 , is shown in  FIG. 6 . The groove is fabricated into the connector-receiving surface opposite the decorated surface  4  of right floor board  3 . The groove consists of five regions arranged sequentially in the direction  30  of tongue insertion. The first region is a recess region defined by recess upper surfaces  47  and  48 . The upper surface  47  of the recess region receives the normal connector base plate  32  and upper surface  48  is receives the base plate extension  56  in  FIG. 5 . The recess region is followed by an entry region defined by converging sidewalls  49  and  50 ; an apex region defined by minimum groove width points  51  and  52 ; a hold region defined by diverging sidewalls  53  and  54 ; and groove cap or termination region defined by surfaces  57  and  58  and by triangular element  63 . The groove sidewall angles are defined as follows: angles  102  and  103  are the left and right entry region convergence angles respectively; and angles  104  and  105  are the left and right hold region divergence angles respectively. The triangular element  63  is part of the groove cap and it may be kept in place or it may be removed with no impact on the operation of the connector system. 
         [0048]    In  FIG. 6 , items  49 ,  51 , and  53  form the right sidewall and items  50 ,  52  and  54  form the left sidewall of its groove. Similarly, in  FIG. 7 , items  49 ,  51 , and  53  form the right sidewall and items  50 ,  52  and  54  form the left sidewall of its groove. 
         [0049]    During connector element insertion into its mating groove, the outward facing nubs on the flexible arms contact the converging walls of the mating groove entry region causing the arms to bend or deflect inward. The maximum deflection occurs when the arm nubs reach the groove apex. The maximum arm bending stress occurs this point, and consequently, the groove minimum width at the apex is selected to avoid significant plastic deformation of the flexible arms as they pass the groove apex during split-tongue insertion. 
         [0050]    Continued insertion of the tongue past the groove apex causes the nubs to contact the diverging walls of the hold region and the associated arm deflection to decrease. The connector becomes fully inserted into its mating groove when the base plate  32  and its extension  56  in  FIG. 5  rest on the groove upper recess surfaces  47  and  48  in  FIG. 6 . The residual arm deflection, i.e., the split-tongue arm deflection at full insertion, though less than that maximum arm deflection associated with the nubs at the groove apex, is significantly not zero. 
         [0051]    The uniform thickness of the normal connector shown in  FIG. 5  make the connector amenable to extrusion via a simple flat plate extrusion die. 
         [0052]    The mating groove for the lateral connector, item  17  in  FIG. 4 , is shown in  FIG. 7 . The groove is fabricated into the joining surfaces of boards  1  and  3  in  FIG. 4 . The lateral connector mating groove shown in  FIG. 7  consists of five regions arranged sequentially in the direction  30  of tongue insertion. These regions are: a recess region defined by recess upper surfaces  59  and  60  to accept base plate extensions  45  and  46  in  FIG. 4 ; an entry region defined by converging sidewalls  49  and  50 ; an apex region defined by minimum groove width points  51  and  52 ; a hold region defined by diverging sidewalls  53  and  54 , and groove cap or termination region  57  and  58 , and by triangular element  63 . The groove sidewall angles are defined as follows: angles  102  and  103  are the left and right entry region convergence angles respectively; and angles  104  and  105  are the left and right hold region divergence angles respectively. The triangular element  63  is part of the groove cap and it may be kept in place or it may be removed with no impact on the operation of the connector system 
         [0053]    In  FIG. 4 , the base plate extensions  45  and  46  of base plate  20  serve two functions:
       1. limit the extent to which the split-tongue can be drawn into the groove and, hence, set the location of the fully inserted split-tongue past the apex and thereby position the connector element so that residual split-tongue arm deflection is established,   2. provide vertical structural support to those portions  28  and  29  of the floor boards that overhang the connector in  FIG. 4 .       
 
         [0056]    In  FIG. 5 , the base plate  32  provides vertical support for those portions  108  and  109  that overhang the normal connector. Base plate  32 , in conjunction with base plate extensions  55  and  56  in  FIG. 5 , act to limit the extent to which the split-tongue can be drawn into its mating groove and, hence, set the location of the fully inserted split-tongue past the apex and thereby position the connector element so that residual split-tongue arm deflection is established. 
         [0057]    A key feature of the normal connector groove structure shown in  FIG. 6  is that the left hold region extension line  65  of said left hold region sidewall  54 ; and the right hold region extension line  66  of said right hold region sidewall  53 , respectively, pass through said groove entrance  67 . Similarly, a key feature of the lateral groove design shown in  FIG. 8  is that the left hold region extension line  68  of said hold region sidewall  54 ; and the right hold region extension line  69  of said left hold region sidewall  53 , respectively, pass through said groove entrance  70 . In contradistinction to the Baker and Vitale groove shown in  FIG. 2 , this allows both grooves to be fabricated using cutters with a cutter diameter greater than the corresponding maximum groove width. That is, with a high-speed cutter such as a circular saw. 
         [0058]      FIG. 8  shows how, subsequent to cutting the base plate recess region  61 , the remainder of the groove can be fabricated via four sequential circular saw cuts made via circular saw blade  62 . The first and second saw cuts are shown in the left and right figures in the upper detail. The third and fourth saw cuts are shown in the left and right figures in the middle detail. The resulting final groove shape is shown in the single detail at the bottom of the figure. 
         [0059]    For each saw cut,  FIG. 8  shows the saw location relative to the floor board and the resulting groove geometry. Though shown in a particular sequential order in  FIG. 8 , these four saw cuts can, actually, be performed in any sequential order. The ability to form the groove using a series of sequential high-speed circular saw cuts is a key feature in allowing the grooves to be fabricated at a linear cutting speed that is high enough for economical flooring production. 
         [0060]      FIG. 9  shows said lateral connector  17  of  FIG. 4  at three significant locations during split-tongue insertion into said mating groove  26 . The upper detail in  FIG. 9  shows the lateral connector  17  and mating groove  26  at the beginning of insertion of the split-tongue into the said mating groove of left floor board  3 . At that point, no arm deflection has been induced by the interaction of the flexible arm nubs with the mating groove sidewall; and, hence, no deflection force is applied to the arms by the groove side walls. The lower left detail in  FIG. 9  shows said connector  17  inserted into said mating groove  26  to the point where the split-tongue flexible arm nubs are in contact with the groove apex. The arms are now deflected in response to forces applied to the arm nubs by the groove sidewalls. The arm deflection  64  is at its maximum value in response to the maximum arm deflecting forces  76  and  77 . The lower right detail in  FIG. 9  shows the connector  17  at full insertion into its mating groove  26 . At full insertion the only intended contact between the flexible arm and the groove is where the nubs contact the hold ramp, the flexible arms should not contact the apex region after full insertion. The corresponding fully inserted arm deflection forces,  78  and  79 , are less than the maximum arm deflection forces  76  and  77  respectively. It should be noted, however, that the fully inserted arm deflection  61 , though less than the maximum arm deflection  64 , is significantly not zero; and consequently, the full insertion arm deflection forces  78  and  79 , though less than the maximum arm deflection forces,  76  and  77 , are similarly, significantly not zero. This is a defining feature of the lateral connector and the mating groove structure. 
         [0061]      FIG. 10  shows two significant locations of the right side of normal connector  31  during insertion into its mating groove  40 . The dotted outlines in the left and right details of  FIG. 10  show the shape and location of split-tongues  36  just prior to full insertion into mating groove  40 . The solid outline in the left detail of  FIG. 10  shows the split-tongue  36  inserted into mating groove  40  to the point where the left and right nubs  100  and  101  respectively on left and right flexible arms  37  and  38  respectively, are in contact with the left and right apex points  52  and  51  respectively of mating groove  40 . The solid outline in the right detail of  FIG. 10  shows the connector  31  fully inserted into mating groove  40  at which point the left and right nubs  100  and  101  respectively on left and right flexible arms  37  and  38  respectively, of split-tongue  36  are in contact with the left and right hold ramp sidewalls  53  and  54  respectively, of mating groove  40 ; and the upper surface support base  32  of connector  31  is in contact with the upper recess surfaces  47  and  48  of mating groove  40 . It is important to note that the flexible arms are intended to not make contact with the groove apex region. 
         [0062]    The left and right flexible arms  37  and  38  respectively in  FIG. 10  are deflected inward in response to forces applied to them by the groove sidewalls. In the left detail of  FIG. 10 , the arm deflection  64  is at its maximum value, and the corresponding arm deflecting forces  76  and  77  are at their maximum values, when the left and right nubs  100  and  101  respectively are at the left and right groove apex points  52  and  51  respectively. The right detail in  FIG. 10  shows the connector  31  at full insertion into mating groove  40 . The left and right nubs  100  and  101  respectively are now in contact with left and right hold ramps  54  and  53  respectively. The corresponding fully inserted arm deflection forces,  78  and  79 , are less than the maximum arm deflection forces  76  and  77  respectively. It should be noted, that the fully inserted arm deflection  61 , though less than the maximum arm deflection  64 , is significantly not zero; and consequently, the full insertion arm deflection forces  78  and  79 , though less than the maximum arm deflection forces  76  and  77 , are similarly, significantly not zero. This is a defining feature of the normal connector and the mating groove structure. 
         [0063]    The geometric interaction between the groove sidewalls and the split-tongue arms is an important feature of the present connector system. As seen in  FIG. 11 , the length of split-tongue arm nubs  98  and  99  is selected so that, at full tongue insertion, contact between the split-tongue arms  37  and  38  and the mating groove sidewall occurs only via nubs  98  and  99  at points  93  and  94  within the diverging or hold region of the groove, and not at the groove apex points  51  and  52  or at any other location along the length of the flexible arms. 
         [0064]    The mechanical interaction between the entry region converging groove sidewalls and the split-tongue flexible arms is an important feature of the present connector system. The left detail in  FIG. 12  shows the right side of a normal connector  31  with split-tongue  36  protruding upward from base support  32 , as said split tongue moves into its mating groove  40 , in the direction of the vertical arrow, from the beginning-of-insertion location (shown by the unshaded connector outline) to the apex-location (shown by the shaded connector outline) where the left and right nubs  100  and  101  respectively contact left and right apexes  52  and  51  respectively of said mating groove. In this detail, the entry region left and right converging sidewalls,  50  and  49 , respectively, of mating groove  40  act to deflect the left and right flexible arms  37  and  38  of split-tongue  36  inwardly (in the direction of the horizontal arrows respectively) as connector element  31  moves into mating groove  40 . 
         [0065]    The right detail of  FIG. 12 , shows in vector format, and in the absence of sidewall-to-nub friction, the force  71  and the force components  72  and  73  imposed on the left flexible arm  37  of split-tongue  36  via nub  100  when said nub is in contact with converging sidewall  49  of said mating groove converging entry region. In the absence of friction, the force  71  is, of necessity, normal to the groove left sidewall surface  49 . Since said left sidewall surface corresponds to the entry region of said groove, angle  97  is negative and corresponds to a converging channel. The force vector  71  acting on the nub is shown decomposed into two orthogonal vector components: a vertically directed force component  72  acting opposite the direction of tongue insertion, and a horizontally directed force component  73  acting normal to the direction of tongue insertion. Force  73  is the force responsible for the inward deflection of the split-tongue left flexible arm  37 . Force component  72  acts in a direction opposite that of split-tongue insertion and, hence, tends to resist entry of the split-tongue  36  into its mating groove  40 . 
         [0066]    Since, in the right detail of  FIG. 12 , the entrance resisting force component  72  acts only on left nub  100  of flexible arm  37  of split-tongue  36 , and since said split-tongue has a second, essentially identical, flexible arm  38 , the total force resisting insertion of said split-tongue into said mating groove is twice the magnitude of force  72 . The condition of zero friction and a −25° value of sidewall angle  97  corresponds to Point A in  FIG. 18  and the corresponding force resisting insertion of the split-tongue into the groove is 0.933 times the value of arm deflection force  73 . The arm deflection force  73  is zero at said beginning-of-insertion location and increases monotonically as the split-tongue moves from that location to said apex-location. Consequently, the force resisting split-tongue insertion of the split-tongue similarly increases monotonically from zero force to its maximum value as the split-tongue moves from said beginning-of-insertion to said apex location. 
         [0067]    A frictionless force interaction between said mating groove sidewall  49  and said left flexible arm nub  100  in  FIG. 12  cannot be achieved in practice and, consequently, the effect of friction on the sidewall-to-nub forces must be taken into account. In the following, as typically done, the friction effect is addressed in terms of an associated friction coefficient. That is, the magnitude of the sidewall friction force  74  acting on the flexible arm nub  100  is given by the product of said friction coefficient and the sidewall surface normal force  71 , and the friction force acts parallel to the sidewall surface and in the direction that opposes the sliding motion of the nub along the sidewall surface. 
         [0068]      FIG. 13 , shows the effect of friction on the forces acting on said left flexible arm nub by said converging groove sidewall  49  of the mating groove entry region. Force vector  71  is the nub force vector component normal to surface  49 ; force vector  74  is the associated friction force vector; and force vector  75  is the resultant force act on the nub. As was done in  FIG. 12 , the resultant force vector  75  is decomposed into a two orthogonal force component vectors: a force vector component  73  responsible for the flexible arm deflection, and a force vector component  72  resisting entry of the nub into the groove. 
         [0069]    The left detail in  FIG. 13  corresponds to a friction coefficient of 0.3. Since there are two flexible arms  37  and  38  on split-tongue  36 , the force resisting entry of said split-tongue into said groove entry region is twice the magnitude of force component  72  in  FIG. 13  and corresponds to Point B in  FIG. 18 , and has a magnitude that is −1.782 times the magnitude of the force component  73  deflecting the split-tongue flexible arm. Said force resisting entry of the split-tongue into said groove entry region has a force magnitude 91% greater than the force magnitude resisting entry of the split-tongue into the groove in  FIG. 12   
         [0070]    The right detail in  FIG. 13  corresponds to a friction coefficient of 0.6. The force component resisting entry of the split-tongue into the mating groove entry region corresponds to Point C in  FIG. 18  and has a magnitude that is −2.961 times the magnitude of the force  73  deflecting the split-tongue flexible arm. This force magnitude is 217% greater than the force magnitude of corresponding force component  72  resisting entry of the split-tongue into the mating groove entry region in  FIG. 12 . 
         [0071]    The mechanical interaction between the hold region diverging groove sidewalls and the split-tongue flexible arms is an important feature of the present connector system. The left detail in  FIG. 14  shows the right side of a normal connector  31  with split-tongue  36  protruding upward from base support  32 , as said split tongue moves into its mating groove  40 , in the direction of the vertical arrow, from said apex-location (shown by the unshaded connector outline) to the fully-inserted-location (shown by the shaded connector outline) where the left and right nubs  100  and  101  respectively contact left and right hold region diverging sidewalls  54  and  53  respectively of said mating groove. In this detail, the hold region left and right diverging sidewalls,  54  and  53 , respectively, of mating groove  40  act to reduce the inward deflection of the left and right flexible arms  37  and  38  of split-tongue  36 ) as connector element  31  moves into mating groove  40 . 
         [0072]    The right detail of  FIG. 14 , shows in vector format, and in the absence of sidewall-to-nub friction, the force  71  and the force components  72  and  73  imposed on the left flexible arm  37  of split-tongue  36  via nub  100  when said nub is in contact with diverging sidewall  54  of said mating groove diverging hold region. In the absence of friction, the force  71  is, of necessity, normal to the groove left sidewall surface  54 . Since said left sidewall surface corresponds to the hold region of said groove, angle  97  is positive and corresponds to a diverging channel. The force vector  71  acting on the nub is shown decomposed into two orthogonal vector components: a vertically directed force component  72  acting in the direction of tongue insertion, and a horizontally directed force component  73  acting normal to the direction of tongue insertion. Force  73  is the force responsible for the inward deflection of the split-tongue left flexible arm  37 . Force component  72  acts in the direction of split-tongue insertion and, hence, tends to aid entry of the split-tongue  36  into mating groove  40 . 
         [0073]    Since, in the right detail of  FIG. 14 , the entrance resisting force component  72  acts only on left nub  100  of flexible arm  37  of split-tongue  36 , and since said split-tongue has a second, essentially identical, flexible arm  38 , the total force resisting insertion of said split-tongue into said mating groove is twice the magnitude of force  72 . For a sidewall angle,  97 , value of +25° and zero nub-to-sidewall friction, the force aiding insertion of the split-tongue into the groove is 0.933 times the force deflecting the split-tongue flexible arm; and corresponds to Point D in  FIG. 18 . The arm deflection force  73  is maximum at said apex-location and decreases monotonically as the split-tongue moves from that location to said fully-inserted-location. Consequently, the frictionless force aiding split-tongue insertion of the split-tongue similarly decreases monotonically from a maximum force value at the apex-location to a lessor force value as the fully-inserted-location. 
         [0074]      FIG. 15 , shows the effect of friction on the forces acting on said left flexible arm nub by said diverging groove sidewall  54  of the said mating hold or diverging wall region. Force vector  71  is the nub force vector component normal to surface  54 ; force vector  74  is the associated friction force vector; and force vector  75  is the resultant force act on the nub. As was done in  FIG. 14 , the resultant force vector  75  is decomposed into a two orthogonal force component vectors: a force vector component  73  responsible for the flexible arm deflection, and a force vector component  72  aiding (or resisting) entry of the nub into the groove. 
         [0075]    The left detail in  FIG. 15  corresponds to a friction coefficient of 0.3. Since there are two flexible arms  37  and  38  on split-tongue  36 , the force resisting entry of the split-tongue into said groove entry region is twice the magnitude of force component  72  in  FIG. 15  and corresponds to Point E in  FIG. 18 , and has a magnitude that is 0.292 times the magnitude of the force component  73  deflecting the split-tongue flexible arm. Said force aiding entry of the split-tongue into said groove entry region has a force magnitude 31% smaller than the force magnitude aiding entry of the split-tongue into the groove in  FIG. 14   
         [0076]    The right detail in  FIG. 15  corresponds to a friction coefficient of 0.9. (The 0.9 friction factor value was selected in this detail, rather than the corresponding value of 0.6 in  FIG. 13 , simply to make the diagram visually clearer.) The force component now resists entry of the split-tongue into the mating groove entry region corresponds to Point F in  FIG. 18  and has a magnitude that is −0.611 times the magnitude of the force  73  deflecting the split-tongue flexible arm. The negative value in  FIG. 18  indicates that the force resists entrance of said split-tongue into said mating groove. 
         [0077]    The left detail in  FIG. 16  shows the right side of a normal connector  31  with split-tongue  36  protruding upward from base support  32 , as said split tongue moves out of its mating groove  40 , in the direction of the vertical arrow, from its fully-inserted-location with left and right nubs  100  and  101  respectively, contacting the diverging sidewalls  54  and  53  location (shown by the unshaded connector outline) to the groove apex-location where said left and right nubs, respectively, are at left and right groove apex locations  52  and  51 , respectively, of said mating groove (shown by the shaded connector outline). In the absence of friction the force acting on the flexible arm nub are independent of the direction of split-tongue motion. Hence the force diagram in the right detail is  FIG. 16  is identical to that in the right detail of  FIG. 14 , and the force resisting retraction of the split tongue from the groove again corresponds to Point D in  FIG. 18 , and the magnitude of the force resisting removal of the split-tongue into the groove is 0.933 times the magnitude of the force deflecting the split-tongue flexible arm. 
         [0078]      FIG. 17 , shows the effect of friction on the forces acting on the right flexible arm nub as the split-tongue is retracted from the groove hold region. Force vector component  71  is the force vector normal to sidewall surface  54 ; force vector  74  is the associated friction force vector component; and force vector  75  is the resultant force vector acting on the nub. As was done in  FIG. 16 , the resultant force  75  is decomposed into two orthogonal force vector components: a force vector component  73  responsible for the flexible arm deflection, and a force component vector  72  aiding or resisting entry of the nub into the groove. 
         [0079]    The left detail in  FIG. 17  corresponds to a friction coefficient of 0.3. The force resisting retraction of the split-tongue into the groove corresponds to Point G in  FIG. 18  and has a magnitude that is 1.782 times the magnitude of the force vector component  73  required to deflect the flexible arm. This force magnitude is 1.91 times greater than the magnitude of corresponding force vector component  72  in  FIG. 16 . The right detail in  FIG. 17  corresponds to a friction coefficient of 0.6. The force resisting entry of the split-tongue into the groove corresponds to Point H in  FIG. 18  and has a magnitude that is 2.961 times the magnitude of the force  73  required to deflect the flexible arm. This force magnitude is 217 times greater than the magnitude of the corresponding force component  72  in  FIG. 16 . 
         [0080]      FIG. 18  is a plot of the ratio of the split-tongue force component in the split-tongue insertion direction to flexible arm deflection force as a function of groove sidewall angle, nub-to-sidewall friction factor, and the direction of split-tongue motion relative to the groove. A positive value corresponds to a force component aiding split-tongue insertion or resisting split-tongue retraction. A negative value corresponds to a force component resisting split-tongue insertion or aiding split-tongue retraction. A negative groove sidewall angle corresponds to the groove entry or converging sidewall region and positive groove sidewall angle corresponds to the groove hold or diverging sidewall region. The solid curves in the figure correspond to the split-tongue moving into the groove and the dashed curves correspond to the split-tongue moving out of the groove. 
         [0081]    For a zero friction factor the force ratio is independent of the motion of the split-tongue relative to the groove and the corresponding curve is shown solid. In this special case the force ratio depends only on the groove sidewall angle and is positive when the sidewall angle is positive (i.e., sidewalls diverging), and is negative when the sidewall angle is negative (i.e., sidewalls converging) 
         [0082]    The actual split-tongue insertion or retraction force is obtained from  FIG. 18  by multiply the above split-tongue force ratio by the flexible arm deflection force. The latter force depends on:
       1. Connector geometry (e.g., flexible arm thickness to flexible arm length)   2. Connector material properties (e.g., flexural modulus)   3. Flexible arm deflection (as limited by the connector material bending yield strength)       
 
         [0086]    Consequently, it is clear that the split-tongue force, in addition to depending on the parameters shown explicitly in  FIG. 18  (i.e., the side-wall angle, friction factor, and direction of split-tongue motion relative to the groove), also depends on the connector geometry and material properties. The latter two factors mean that the connector system insertion and retraction forces can be changed simply by changing the connector material or geometry and without any corresponding changes to the groove geometry. 
         [0087]    In  FIG. 18 , Point A corresponds to the right detail in  FIG. 12  and Points B and C correspond to the left and right details of  FIG. 13  respectively; Points D corresponds to right detail in  FIGS. 14 and 16 , and Points E and F correspond to the left and right details of  FIG. 15  respectively; Points G and H correspond to the left and right details of  FIG. 17  respectively. 
         [0088]    The preferred embodiment of the connector system described above, is characterized by eleven features:
       1. Split-tongues having two flexible arms.   2. Outward facing nubs at the distal end of each flexible arm.   3. A base plate with two split-tongues projecting in the same direction from its ends or projecting in opposite directions from its faces.   4. Base plate extensions on either end of the base plate   5. A mating groove consisting of a recess region, a converging entry region, a minimum width apex region, a diverging hold region, and a cap or termination region arranged sequentially in the direction of tongue insertion.   6. Hold region extension lines that pass with margin through the entrance region of the groove.   7. Contact between the flexible arms and the groove sidewalls occurring only at the distal end of the flexible arm nubs   8. Further full insertion motion of the split-tongue into the groove is prevented by contact of the split-tongue base plate with the mating groove recess region upper surfaces.   9. Significant nonzero full insertion residual deflection.   10. Insertion and hold region force components that can be changed by changing the convergence angle of the converging insertion region and the divergence angle of the diverging hold region respectively.   11. Insertion and hold region force components that can be changed by changing the connector geometric parameters (e.g., the ratio of thickness of the flexible arms to their length) or by changing its material parameters (e.g., the connector material flexural modulus).       
 
         [0100]      FIG. 19  shows an alternate connector configuration  80  and an alternate mating groove configuration  81 . In the left detail in  FIG. 19 , the right and left outward facing protruding nubs  93  and  94 , respectively, at the distal ends of right and left flexible arms  87  and  8 , respectively, are modified to form right and left insertion ramps  85  and  86  respectively. The presence of said insertion ramps, can be used to advantage to reduce the magnitude of convergence angle of the mating groove entry or converging sidewall region. 
         [0101]    In the right detail in  FIG. 19 , the converging angle of the entry region of the mating groove is reduced to zero. In the preferred embodiments, the converging mating groove sidewalls  49  and  50  in  FIGS. 6 and 7  act to deflect the split-tongue flexible arms inward during the initial stages of the split-tongue entry into its mating groove as shown in schematically in left detail in  FIG. 12 . 
         [0102]    As shown in  FIG. 20 , the inward deflection of the split-tongue arms during initial stages of split-tongue insertion into the groove is accomplished in the alternate connector configuration via the interaction of the right and left inlet corners  89  and  90 , respectively, with the right and left entry ramps  85  and  86 , respectively, as the split-tongue is moved in the direction of arrow  92 . 
         [0103]      FIG. 21  shows the flexible arms  87  and  88  of alternate connector  80  at maximum inward deflection in. At this condition, flexible arm nubs  93  and  94  ride along the parallel sidewall surfaces  82  and  83  of groove  91 . Motion of connector  80  in the direction of insertion arrow  92 , at this point is hindered only by friction between nubs  93  and  94  and sidewall surfaces  82  and  83 . 
         [0104]      FIG. 22  shows the split-tongue comprising flexible arms  87  and  88  of alternate connector  80  fully inserted into its mating groove. In this condition nubs  93  and  94  interact with the diverging sidewalls  53  and  54  of groove  91  so as to generate a force component that tends to draw connector  80  into the groove. Further entrance of connector  80  into groove  91  is prevented by contact of base plate extensions  45  and  46  with the recess region upper surfaces  95  and  96  respectively of the mating groove  91 . 
         [0105]    In  FIG. 12  the inward deflection of the split-tongue flexible arms  37  and  38  as the split-tongue moves into its mating groove  40  is accomplished solely by the action of the mating groove entry region converging sidewalls  50  and  51  on the split-tongue flexible arm nubs  100  and  101 . In  FIG. 20 , the inward deflection of the split-tongue flexible arms  87  and  88  as the split-tongue is inserted into its mating groove  91  is accomplished solely by the action of the inlet corners  89  and  90  on the nub entry ramps  85  and  86 . In  FIG. 20  the convergence angle of the mating groove entry region is zero, and the entry region sidewalls  82  and  83  are parallel. 
         [0106]    It clear that an intermediate structure between that shown in  FIG. 12  and that shown in  FIG. 19  can be had in the entry region sidewall convergence angle is less than that shown in  FIG. 12  but greater than that shown in  FIG. 19 . In that case, as the split-tongue is inserted into its mating groove, an initial fraction of the total inward deflection of the split-tongue flexible arms is accomplished by the inlet corners  89  and  90  acting on the nub entry ramps  85  and  86  in a manner similar to that shown  FIG. 20 ; followed by the remaining fraction of inward deflection being accomplished by the mating groove entry region converging sidewalls acting on the flexible arm outward facing nubs in a manner similar to that shown in  FIG. 12 . 
         [0107]    In  FIG. 19 , the alternate connector is shown for a lateral connector configuration. A lateral connector is one whose two split-tongues, such as items  18  and  19  in  FIG. 4  are formed on either side its base plate  20 ). As is the case with a lateral connector, its mating groove structure is shown fabricated into the side edge of the associated floor board as shown in  FIG. 7 . It is clear, however, that the same alternate split-tongue structure can just as easily be adapted to the normal connector shown in  FIG. 5  and the mating groove integrated into the bottom surface of its associated floor board as shown in  FIG. 6 .