Abstract:
A method and apparatus for folding a case along a hinge where the hinge is designed to project the neutral bend access of the fold to a layer affixed to an outer surface of the case.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims priority to U.S. provisional application 62/279,476 filed on Jan. 15, 2016, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a method for folding an electronic device with a flexible display where the device case hinges such that the display experiences neither a tension nor compression force when the device is folded. 
         [0004]    2. Statement of the Problem 
         [0005]    It is convenient to be able to fold a mobile electronic device. Folding a tablet sized device, for example, would allow it to fit in a user&#39;s pocket. Folding displays are becoming possible with the advent of OLED displays processed on thin flexible substrates. These displays, however, are complex laminates comprised of numerous materials with varying elasticities. So, though they can bend, they are not easily compressed and stretched. When a laminate is bent, there is a neutral bend axis where the material experiences neither a compression nor a tension stress. The material outside this axis experiences tension stresses while the material inside this axis experiences compression stresses. It is preferable for this neutral bend axis be reserved for the layer in the display least able to withstand these stresses. 
         [0006]    It is often desirable for the display on a mobile device to be mounted to a case that can act as a base for the display and contain electronics, batteries, and the like. To be able to fold the device, the case will require a hinge. Traditional hinges contain the neutral bend axis, thus causing tension or compression stress in the display mounted to the case as the device is folded. 
       SUMMARY OF THE SOLUTION 
       [0007]    The present invention solves the above and other problems with a hinge that is able to project the neutral bend axis to a location above or below it. 
       Aspects 
       [0008]    An aspect of the invention is how the hinge is comprised of two hinge layers where each hinge layer is comprised of two or more segments connected end to end with pivots pins, and where each hinge layer contains the same number segments, and where each segment in the first hinge layer is paired with a segment in the second hinge layer, and where the center point of the pared segments are tied together, and where the length of the segments on the first layer can be varied and the length of the segments in the second hinge layer can be varied. 
         [0009]    Another aspect of the invention is how the hinge lays flat when the lengths of the segments in the first hinge layer are equal to the length of the segments in the second hinge layer. 
         [0010]    Another aspect of the invention is how the hinge curls towards the first hinge layer when the length of the segments in the first hinge layer are less than the length of the segments in the second hinge layer. Likewise, the hinge curls towards the second hinge layer when the length of the segments in the first hinge layer are greater than the lengths of the segments in the second hinge layer. 
         [0011]    Another aspect of the invention is how the length of an arc swept by the hinge can be increased and decreased by proportionately increasing and decreasing the lengths of the segments in the first and second hinge layers. 
         [0012]    Another aspect of the invention is how the degrees of the bend formed by the hinge can be increased and decreased by increasing and decreasing the lengths of the segments in one hinge layer with respect to the lengths of the segments in the other hinge layer. 
         [0013]    Another aspect of the invention is how the lengths of the segments in the first hinge layer and the lengths of the segments in the second hinge layer can be varied to cause the hinge to open and close while keeping the neutral bend axis a set distance from the pivot points connecting the segments in the first hinge layer. 
         [0014]    Another aspect of the invention is how each hinge segment is comprised of a pair of cross ties where the length of the segment is varied by varying the angle between the cross ties, and where adjacent cross ties within each hinge layer can be tied together so the lengths of the segments within a hinge layer remain equal as they increase and decrease. 
         [0015]    Alternatively, each hinge segment is comprised of a pair of parallel plates where the length of the segment is varied by sliding the plates relative to one another. 
         [0016]    Another aspect of the invention is how a device can be comprised of any number of case pieces (n) connected by (n−1) hinges 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other advantages and features of the invention may be better understood from a reading of the detailed description taken in conjunction with the drawings. The same reference number represents the same element on all drawings. 
           [0018]      FIG. 1A  is a side view of a bi-folding device where the neutral bend axis is inside the hinge.  FIG. 1B  is a side view of a bi-folding device when the hinge is lying flat.  FIG. 1C  is a side view of a bi-folding device where the neutral bend axis is outside the hinge. 
           [0019]      FIG. 2A  is a top view of the cross tie assembly between two adjacent pairs of pivots when the bi-folding device is folded so the neutral bend axis is inside the hinge.  FIG. 2B  is a top view of the cross tie assembly between two adjacent pairs of pivots when the bi-folding device is lying flat.  FIG. 2C  is a top view of the cross tie assembly between two adjacent pairs of pivots when the bi-folding device is folded so the neutral bend axis is outside the hinge. 
           [0020]      FIG. 3A  is a simplified side view of two adjacent pairs of pivots where the neutral bend axis is outside the hinge.  FIG. 3B  is a simplified side view of two adjacent pairs of pivots where the neutral bend axis is inside the hinge. 
           [0021]      FIG. 4A  is a simplified top view of the cross ties when the bi-folding device is folded so the neutral bend axis is inside the hinge.  FIG. 4B  is a simplified top view of the cross ties when the bi-folding device is lying flat.  FIG. 4C  is a simplified top view of the cross ties when the bi-folding device is folded so the neutral bend axis is outside the hinge. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIGS. 1-4  and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents. 
         [0023]      FIG. 1  shows three folding configurations of device  100 : in  FIG. 1A  device  100  is folded with the neutral bend axis is inside the hinge, in  FIG. 1B  device  100  is folded with the neutral bend axis beside the hinge, and in  FIG. 1C  device  100  is folded with the neutral bend axis outside the hinge. 
         [0024]    The bi-folding device  100  consists of a display laminate  107  covering two case enclosure pieces  101  and  106  connected by two hinge layers where each layer is comprised of five link segments each. Each link segment within the first hinge layer is paired with a link segment in the second hinge layer. For example, link segment  110  is paired with link segment  120 . The link segments are constructed in a manner that allows them to expand and contract. In a preferred embodiment, all the link segments within the first hinge layer are the same length and all the segments within the second hinge layer are the same length. 
         [0025]    The link segments within a hinge layer are connected to one another and the case pieces at pivot pins. For example, link segment  110  is connected to link segment  112  via pivot pin  111 . These pivot pins allow the segments to rotate relative to one another. 
         [0026]    The paired link segments between hinge layers are tied together at the links&#39; center points. 
         [0027]    The ability of the links to expand and contract combined with their ability to rotate, allow the hinge to open and close while keeping display  107  on the neutral bend axis. 
         [0028]      FIG. 2  shows the top and end views of a link represented by link pair  114 / 124 . It shows the details of the mechanism in three different states.  FIG. 2A  shows the mechanism where the neutral bend axis would be inside the hinge.  FIG. 2B  shows the mechanism where the neutral bend axis would be beside the hinge.  FIG. 2C  shows the mechanism where the neutral bend axis would be outside the hinge. 
         [0029]    In this embodiment, each link pair is implemented as a single link mechanism  200 . Link mechanism  200  consists of two cross ties  201  and  203  connected at pivot point  202 , and eight sleeves that connect it to four pivot pins. The cross tie is connected to each pivot pin via two sleeves. The geometry of the link mechanism allows the distance between the pivot pins in each hinge layer to expand and contract where the relationship of first layer distance to the second layer distance follows a deterministic function. 
         [0030]      FIG. 3A  shows a representation of link pair  114 / 124  when the neutral bend axis is outside the hinge.  FIG. 3A  shows a representation of link pair  114 / 124  when the neutral ben axis is outside the hinge. As can be derived from these diagrams, if
       Θ is the total angle of the case bend divided by the number of segment pairs,   h is the fixed distance between paired pivot pins,   d is a defined gap between the hinge mechanism and the neutral bend axis,   a is the length of the arc swept out over the link segment,   r is the radius of the arc,   l 1  is the distance between the pivot pin pairs on hinge layer 1, and   l 2  is the distance between the pivot pin pairs on hinge layer 2, then       
 
         [0000]        l 1=2·( r−d )·sin(Θ/2) and
 
         [0000]        l 2=2·( r−d−h )·sin(Θ/2) for FIG.  3 A
 
         [0000]        l 1=2·( r+d )·sin(Θ/2) and
 
         [0000]        l 2=2·( r+d+h )·sin(Θ/2) for FIG.  3 B
 
         [0000]        a/ 2π r=Θ/ 2π
 
         [0000]    Along the neutral bend axis there is no stretching or compressing so “a” is held constant. Thus “r” will vary as “Θ” varies. Rearranging and substituting yields: 
         [0000]        l 1=2·( a/Θ−d )·sin(Θ/2) and
 
         [0000]        l 2=2·( a/Θ−d−h )·sin(Θ/2) for FIG.  3 A
 
         [0000]        l 1=2·( a/Θ+d )·sin(Θ/2) and
 
         [0000]        l 2=2·( a/Θ+d+h )·sin(Θ/2) for FIG.  3 B
 
         [0038]      FIG. 4  shows a representation of link pair  114 / 124  in various states. As can be derived from these diagrams: 
         [0000]        l 1=2· r 1·sin θ2
 
         [0000]        l 2=2· r 2·sin(θ2+θΔ)
 
         [0000]    where r 1 , r 2 , and ΘΔ are fixed based on the design of the cross tie. 
         [0039]    The table of calculations below show a design example where carefully selected values for “do”, “r 1 ”, and “r 2 ” based on given design specifications will keep the display on the neutral bend axis as the case is folded by varying θ 2 . 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Design Specifications 
                   
               
             
          
           
               
                   
                 Minimum bend radius 
                 7.500 
                 mm 
               
             
          
           
               
                   
                 Maximum bend angle 
                 190.000°  
               
               
                   
                 Number of links 
                 5 
               
             
          
           
               
                   
                 Distance between paired  
                 2.400 
                 mm 
               
               
                   
                 pivots (h) 
                   
                   
               
               
                   
                 Distance from hinge to  
                 1.700 
                 mm 
               
               
                   
                 inside neutral bend  
                   
                   
               
               
                   
                 axis (di) 
                   
                   
               
             
          
           
               
                   
                 Selected Values 
                   
               
             
          
           
               
                   
                 Distance from hinge  
                 1.535 
                 mm 
               
               
                   
                 to outside neutral 
                   
                   
               
               
                   
                 bend axis (do) 
                   
                   
               
               
                   
                 Cross tie radius to hinge  
                 5.000 
                 mm 
               
               
                   
                 layer 1 (r1) 
                   
                   
               
               
                   
                 Cross tie radius to hinge  
                 11.058 
                 mm 
               
               
                   
                 layer 2 (r2) 
                   
                   
               
             
          
           
               
                   
                 Calculated Values 
                   
               
             
          
           
               
                   
                 Arc length (a) (calculate  
                 4.974 
                 mm 
               
               
                   
                 when Φ = maximum 
                   
                   
               
               
                   
                 bend angle) 
                   
                   
               
             
          
           
               
                   
                 Cross tie angle delta (θΔ)  
                 16.832°  
               
               
                   
                 (calculate when Φ = 0 
                   
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Total 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Bend 
                   
                 Target 
                 Target 
                   
                   
                 Actual 
                 Actual 
                 d error 
               
               
                 Angle° 
                 Φ° 
                 11 mm 
                 12 mm 
                 θ1° 
                 θ2° 
                 11 mm 
                 12 mm 
                 mm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 −190 
                 −38 
                 3.884 
                 2.322 
                 22.857 
                 6.026 
                 3.884 
                 2.322 
                 0.000 
               
               
                 −180 
                 −36 
                 3.944 
                 2.461 
                 23.231 
                 6.399 
                 3.944 
                 2.465 
                 0.005 
               
               
                 −170 
                 −34 
                 4.004 
                 2.601 
                 23.605 
                 6.773 
                 4.004 
                 2.608 
                 0.010 
               
               
                 −160 
                 −32 
                 4.064 
                 2.741 
                 23.978 
                 7.146 
                 4.064 
                 2.751 
                 0.014 
               
               
                 −150 
                 −30 
                 4.123 
                 2.881 
                 24.351 
                 7.519 
                 4.123 
                 2.894 
                 0.019 
               
               
                 −140 
                 −28 
                 4.182 
                 3.021 
                 24.723 
                 7.892 
                 4.182 
                 3.037 
                 0.023 
               
               
                 −130 
                 −26 
                 4.241 
                 3.161 
                 25.095 
                 8.264 
                 4.241 
                 3.179 
                 0.028 
               
               
                 −120 
                 −24 
                 4.300 
                 3.302 
                 25.466 
                 8.635 
                 4.300 
                 3.320 
                 0.032 
               
               
                 −110 
                 −22 
                 4.358 
                 3.442 
                 25.837 
                 9.005 
                 4.358 
                 3.462 
                 0.037 
               
               
                 −100 
                 −20 
                 4.416 
                 3.583 
                 26.206 
                 9.375 
                 4.416 
                 3.602 
                 0.041 
               
               
                 −90 
                 −18 
                 4.474 
                 3.723 
                 26.575 
                 9.743 
                 4.474 
                 3.743 
                 0.046 
               
               
                 −80 
                 −16 
                 4.531 
                 3.863 
                 26.942 
                 10.111 
                 4.531 
                 3.882 
                 0.050 
               
               
                 −70 
                 −14 
                 4.588 
                 4.003 
                 27.308 
                 10.477 
                 4.588 
                 4.022 
                 0.054 
               
               
                 −60 
                 −12 
                 4.644 
                 4.143 
                 27.673 
                 10.842 
                 4.644 
                 4.160 
                 0.058 
               
               
                 −50 
                 −10 
                 4.700 
                 4.282 
                 28.037 
                 11.205 
                 4.700 
                 4.298 
                 0.062 
               
               
                 −40 
                 −8 
                 4.756 
                 4.421 
                 28.399 
                 11.567 
                 4.756 
                 4.435 
                 0.066 
               
               
                 −30 
                 −6 
                 4.811 
                 4.560 
                 28.759 
                 11.928 
                 4.811 
                 4.571 
                 0.071 
               
               
                 −20 
                 −4 
                 4.866 
                 4.699 
                 29.118 
                 12.286 
                 4.866 
                 4.706 
                 0.075 
               
               
                 −10 
                 −2 
                 4.920 
                 4.837 
                 29.475 
                 12.643 
                 4.920 
                 4.841 
                 0.079 
               
               
                 0 
                 0 
                 4.974 
                 4.974 
                 29.829 
                 12.998 
                 4.974 
                 4.974 
                 0.000 
               
               
                 10 
                 2 
                 5.033 
                 5.117 
                 30.220 
                 13.389 
                 5.033 
                 5.121 
                 0.078 
               
               
                 20 
                 4 
                 5.092 
                 5.259 
                 30.609 
                 13.778 
                 5.092 
                 5.267 
                 0.074 
               
               
                 30 
                 6 
                 5.150 
                 5.401 
                 30.997 
                 14.165 
                 5.150 
                 5.412 
                 0.070 
               
               
                 40 
                 8 
                 5.207 
                 5.542 
                 31.381 
                 14.550 
                 5.207 
                 5.556 
                 0.065 
               
               
                 50 
                 10 
                 5.264 
                 5.683 
                 31.764 
                 14.932 
                 5.264 
                 5.699 
                 0.061 
               
               
                 60 
                 12 
                 5.320 
                 5.822 
                 32.144 
                 15.312 
                 5.320 
                 5.840 
                 0.056 
               
               
                 70 
                 14 
                 5.376 
                 5.961 
                 32.522 
                 15.690 
                 5.376 
                 5.981 
                 0.052 
               
               
                 80 
                 16 
                 5.431 
                 6.099 
                 32.896 
                 16.065 
                 5.431 
                 6.120 
                 0.048 
               
               
                 90 
                 18 
                 5.486 
                 6.237 
                 33.269 
                 16.437 
                 5.486 
                 6.258 
                 0.043 
               
               
                 100 
                 20 
                 5.539 
                 6.373 
                 33.638 
                 16.806 
                 5.539 
                 6.394 
                 0.039 
               
               
                 110 
                 22 
                 5.592 
                 6.508 
                 34.004 
                 17.172 
                 5.592 
                 6.530 
                 0.035 
               
               
                 120 
                 24 
                 5.645 
                 6.643 
                 34.366 
                 17.535 
                 5.645 
                 6.663 
                 0.030 
               
               
                 130 
                 26 
                 5.696 
                 6.776 
                 34.725 
                 17.894 
                 5.696 
                 6.795 
                 0.026 
               
               
                 140 
                 28 
                 5.747 
                 6.909 
                 35.081 
                 18.250 
                 5.747 
                 6.926 
                 0.022 
               
               
                 150 
                 30 
                 5.798 
                 7.040 
                 35.433 
                 18.602 
                 5.798 
                 7.055 
                 0.017 
               
               
                 160 
                 32 
                 5.847 
                 7.170 
                 35.781 
                 18.950 
                 5.847 
                 7.182 
                 0.013 
               
               
                 170 
                 34 
                 5.896 
                 7.299 
                 36.126 
                 19.294 
                 5.896 
                 7.308 
                 0.009 
               
               
                 180 
                 36 
                 5.943 
                 7.427 
                 36.466 
                 19.634 
                 5.943 
                 7.431 
                 0.004 
               
               
                 190 
                 38 
                 5.990 
                 7.553 
                 36.802 
                 19.970 
                 5.990 
                 7.553 
                 0.000 
               
               
                   
               
             
          
         
       
     
         [0040]    The error shown in the last column is easily accommodated by an elastomer layer that fills the gap and smooths the discontinuities between the hinge mechanism and the display laminate. Because this elastomer is not on the neutral bend axis, it is selected based on its Poisson ratio to match the reduction in the gap from “di” when the elastomer is compressed, to “do” when the elastomer is stretched. 
         [0041]    Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents therein.