Abstract:
The invention relates to a mechanical finger comprising, a knuckle, a proximal element, a rod, a motor, a motor driven screw and a distal element. The knuckle has a first and second pivot. The proximal element knuckle end is coupled to the first pivot. The proximal element also has a third pivot at a variable longitudinal distance from the first pivot. The rod has a near end pivotally coupled to the second pivot and a far end pivotally coupled to the third pivot. A motor is coupled to and referenced to the proximal element. A screw is driven to change the distance between the third pivot and the first pivot in response to a command from a controller to the motor. A distal element is pivotally coupled to the proximal element. The distal element rotates with respect to the proximal element in response to a change in the variable distance between the third pivot and the first pivot.

Description:
[0001]    This invention claims priority from provisional patent application Ser. 61/780,622 filed 13 Mar. 2013 for a Prosthetic Finger Design having a common sole inventor. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    This invention was not developed with Government funded effort. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to the field of prosthetic appliances made for and used by human amputees and more particularly to those amputees that have lost one or more fingers on a hand. 
       BACKGROUND OF THE INVENTION 
       [0004]    U.S. Pat. No. 8,100,986 issued on Jan. 24, 2012 to inventor Gregor Puchhammer of Vienna (AT) shows a mechanical prosthetic finger with a proximal member, a medial member and a distal member all mounted pivotally on one another. A moveable balance arm is connected via leavers to the proximal member and to the distal member. However the Puchhammer ‘986’ reference does not show the simpler arrangement of a screw nut assembly in a proximal element cavity having a left and right pivot boss extending through the left and right slots in the proximal element cavity. The left and right pivot boss are each sized to provide free longitudinal movement within its respective left guide and right slots so as to prevent the screw nut assembly from rotating in the proximal element cavity as the screw nut assembly is moved longitudinally in the proximal element cavity by a an axial screw drive. 
         [0005]    U.S. Pat. No. 5,888,246 issued Mar. 30, 1999 to inventor David J. Gow of Edinburgh (GB) from application Ser. No. 08/702,605 filed Mar. 10, 1995. The ‘246’ patent is related art but it fails to show a screw nut assembly in a proximal element cavity having a left guide and pivot boss extending through the left slot and a right guide and pivot boss extending through the right slot of the proximal element cavity. The left and right pivot boss are each sized to provide free longitudinal movement of the left and right boss toward the distal element or toward the knuckle end of the proximal element within its respective left guide or right guide while preventing the screw nut assembly from rotating in the proximal element cavity as the screw nut assembly is moved longitudinally in the proximal element cavity by a direct longitudinal screw drive. 
         [0006]    Mechanical fingers for artificial hands require various features to best perform the functions for an upper limb prosthetic user. The required features and functions include a high strength force generator, a light weight, good reliability, adequate speed, and a size that permits a cover that provides a natural appearance. These features are made difficult to include by the small space available inside an individual finger. 
         [0007]    Another feature that is difficult to achieve in the design of a prosthetic mechanical finger is the short section where the prosthetic finger attaches to the residual end of the finger on the patient. Previous embodiments have placed the force generators or a part of the drive mechanism inside the build height which extends the length of the prosthetic to a position that is outside of the natural envelope of a finger. A longer than natural build height tends to result in fewer patients being fitted with a prosthetic finger. The shorter build height made possible by the invention is expected to improve the market acceptance of the prosthetic with expanded sales including sales to female s and teenagers. 
         [0008]    Another feature made possible by the invention prosthetic is a reduced cost flowing from its reduced complexity. Earlier embodiments have higher part counts with parts of significant complexity that contributed to a higher price for the prosthetic. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to solve or reduce many of the problems stated above. The mechanical finger as taught by this disclosure, in a first embodiment that comprises the following components as referenced in  FIGS. 1 a -1 c   : a knuckle ( 12 ), a proximal element ( 24 ), a rod ( 18 ), a screw nut boss ( 22 ), a force generator ( 26 ) with an axial drive shaft driving a screw that is axially coupled to the screw nut assembly, and a frame ( 10 ) means for coupling the knuckle ( 12 ) to the stump or residual limb of the patient. The knuckle ( 12 ) is coupled to the frame ( 10 ) and has a first ( 14 ) and second pivot ( 16 ) separated by a first predetermined distance. The proximal element has a knuckle end and a distal end. The knuckle end of the proximal element is coupled to the knuckle first pivot ( 14 ). The proximal element provides a third pivot ( 21 ). The third pivot is located on the proximal element ( 24 ) at a variable longitudinal distance from the first pivot ( 14 ). 
         [0010]    It should be understood that the each of the three pivots characterized herein, and later a fourth pivot, are characterized in the structure of the invention mechanical finger by a corresponding left and right counterpart, each left and right counterpart being axially aligned, the axis of each pivot being normal to a plane that contains the longitudinal axis of the axial screw drive to the screw nut assembly. 
         [0011]    The rod ( 18 ) having a near end pivotally coupled to the knuckle second pivot ( 16 ) and a far end of the rod ( 18 ) is pivotally coupled to the third pivot ( 21 ). A screw ( 74 ) drives the screw nut boss ( 22 ). The force generator ( 26 ) is coupled to or reference to the proximal element ( 24 ), and more particularly to the near end or knuckle end of the proximal element cavity. The screw ( 74 ) is coupled to the third pivot ( 21 ) to change the variable longitudinal distance between the third pivot ( 21 ) and the first pivot ( 14 ) in response to a command from a controller to the force generator ( 26 ). 
         [0012]    A distal element ( 38 ) is pivotally coupled to the proximal element at a fourth pivot ( 36 ). The distal element ( 38 ) rotates with respect to the proximal element ( 24 ) in response to a change in the variable distance between the third pivot ( 21 ) and the first pivot ( 14 ). The distal element ( 38 ) further has at least a first phalange pivotally coupled to the fourth pivot ( 36 ) on the proximal element ( 24 ). Each phalange has a distal element follower aperture ( 47 ) characterized to receive a screw nut boss ( 22 ) through a proximal element slot ( 42 ) then passing through the distal element follower aperture ( 47 ). 
         [0013]    Movement of the screw nut boss ( 22 ) toward the knuckle ( 12 ) results in a counter clockwise torque applied to the distal element ( 38 ) around the fourth pivot ( 36 ) as the screw nut boss ( 22 ) engages the wall of the distal element follower aperture ( 47 ). Movement of the screw nut boss ( 22 ) toward the distal end of the proximal element ( 24 ) results in a clockwise torque applied to the distal element ( 38 ) around the fourth pivot ( 36 ) as the screw nut boss ( 22 ) engages the wall of the distal element follower aperture ( 47 ). In another alternative embodiment, the mechanical finger comprises a frame coupled to the knuckle and formed to receive and be attached to the residual limb of a patient. The mechanical finger also has an elastic or spring element ( 46 ) extending in tension from the distal element ( 38 ) to the proximal element ( 24 ) to add to the grip force of the finger as it closes and to help to maintain a limited closed grip on the object grasped as the power to the force generator is interrupted. 
         [0014]    The screw nut assembly within the proximal element cavity has a left guide and pivot boss extending through a left slot and a right guide and pivot boss extending through a right slot, each guide and pivot boss extending through its respective slot. As explained above, the force generator or motor rotates the screw that is engaged with the screw nut assembly. The screw nut assembly carries the left and right pivot boss in its slot, each pivot boss being sized to provide free longitudinal movement within its respective left guide and right guide to prevent the screw nut assembly from rotating in the proximal element cavity. The rotation of the screw is transferred into a linear movement of the third pivot as the screw nut assembly is moved longitudinally through the proximal element cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    An example of a mechanical finger embodying the present invention will now be described in greater detail with reference to the accompanying drawings, in which; 
           [0016]      FIG. 1 a    shows a schematic stick drawing of the mechanical finger in the fully open position 
           [0017]      FIG. 1 b    shows a schematic stick drawing of the mechanical finger in a partially flexed position 
           [0018]      FIG. 1 c    shows a schematic stick drawing of the mechanical finger in a fully flexed position 
           [0019]      FIG. 2 a    is a perspective view of the mechanical finger shown in the fully open position 
           [0020]      FIG. 2 b    is a perspective view of the mechanical finger shown in a partially flexed position 
           [0021]      FIG. 2 c    is a perspective view of the mechanical finger shown in fully flexed position 
           [0022]      FIG. 3 a    shows a partial sectional perspective view of the mechanical finger in the fully open position, showing the drive mechanism 
           [0023]      FIG. 3 b    shows a partial sectional perspective view of the mechanical finger in the partially closed position, showing the drive mechanism 
           [0024]      FIG. 3 c    shows a partial sectional showing the drive mechanism in a perspective view of the mechanical finger in the fully closed position, 
           [0025]      FIG. 4 a    is a perspective view of the mechanical finger, 
           [0026]      FIG. 4 b    is a perspective exploded view of  FIG. 4   a,    
           [0027]      FIG. 5 a    shows a plan view of the mechanical finger with a section line A-A 
           [0028]      FIG. 5 b    shows the section view A-A 
           [0029]      FIG. 6 a    is a perspective view of the distal element 
           [0030]      FIG. 6 b    shows an exploded view  FIG. 6 a      
           [0031]      FIG. 7 a    is a perspective view of the force generator and the drive mechanism, 
           [0032]      FIG. 7 b    shows an exploded view of  FIG. 7 a      
           [0033]      FIG. 8 a    is a perspective view of the proximal element, 
           [0034]      FIG. 8 b    shows an exploded view of  FIG. 8 a      
           [0035]      FIG. 9 a    is a perspective view of the knuckle to frame mount and frame mount assembly, 
           [0036]      FIG. 9 b    shows an exploded view of  FIG. 9 a      
           [0037]      FIG. 10 a    shows a side view of the rod 
           [0038]      FIG. 10 b    shows a plan view of the rod 
           [0039]      FIG. 10 c    shows an exploded view of the rod with bearings 
           [0040]      FIG. 10 d    shows the rod with bearings fitted 
           [0041]      FIG. 11 a    shows a side view of the screw nut 
           [0042]      FIG. 11 b    shows a front view of the screw nut 
           [0043]      FIG. 11 c    shows a perspective view of the screw nut with ×2 washers 
           [0044]      FIG. 11 d    shows a perspective view of the screw nut with ×2 washers 
           [0045]      FIG. 11 e    shows a perspective view of the screw nut with ×4 washers fitted 
           [0046]      FIG. 11 f    shows a perspective view of the screw nut with ×4 washers fitted 
           [0047]      FIG. 12 a    shows the sprung element side view 
           [0048]      FIG. 12 b    shows the sprung element in perspective 
           [0049]      FIG. 13 a    is a perspective and partial view of the proximal element and screw nut in the fully open position 
           [0050]      FIG. 13 b    is a perspective and partial view of the proximal element and screw nut in the partially closed position 
           [0051]      FIG. 13 c    is a perspective and partial view of the proximal element and screw nut in the fully closed position 
           [0052]      FIG. 14 a    is a perspective and partial view of the proximal element, screw nut and distal element in the fully open position 
           [0053]      FIG. 14 b    is a perspective and partial view of the proximal element, screw nut and distal element in the partially closed position 
           [0054]      FIG. 14 c    is a perspective and partial view of the proximal element, screw nut and distal element in the fully closed position 
           [0055]      FIG. 15 a    is a perspective and partial view of the proximal element, rod and distal element in the fully open position 
           [0056]      FIG. 15 b    is a perspective and partial view of the proximal element, rod and distal element in the partially closed position 
           [0057]      FIG. 15 c    is a perspective and partial view of the proximal element, rod and distal element in the fully closed position 
           [0058]      FIG. 16 a    shows a partial view of the proximal element, rod and distal element in the fully open position, the distal element having an alternative slot design 
           [0059]      FIG. 16 b    shows a partial view of the proximal element, rod and distal element in the fully open position, the distal element having an alternative slot design and the distal element being pushed closed 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0060]    The invention Mechanical Finger will now be discussed with reference to  FIG. 1  through  FIG. 16 b    with  FIG. 1 a    being a simplified stick drawing showing frame  10  which attaches to the amputee residual limb, and the knuckle  12  attached to the frame  10 . The knuckle  12  has a proximal element to knuckle pivot  14  and a rod to knuckle pivot  16 . The knuckle end of the rod  18  is attached to the knuckle  12  at the rod to knuckle pivot  16 . The distal end of the rod  18  is attached to the rod to screw nut boss  22 . The proximal element  24  contains the force generator  26  that is connected to and can push and pull the screw nut boss  22  in a longitudinal direction. The force generator  26  is powered by the battery  28 , and controlled by the control sensor  32  and the processor  34 . The proximal element  24  has a proximal element to distal element pivot  36  which connects the proximal element  24  to the distal element  38 . The proximal element  24  has a proximal element slot  42  that guides the screw nut boss  22  in a longitudinal direction. The distal element  38  has a distal element follower aperture  47  which contains the screw nut boss  22 . As the force generator actuates the screw nut boss  22 , the distal element follower aperture  47  accommodates the linear movement of the screw nut boss  22  as it travels through the arc from the proximal element to distal element pivot  36  and pulls the distal element  38  closed. The elastic or spring element  46  is connected to the distal element  38  and the proximal element  24  to maintain force when the power is interrupted. 
         [0061]      FIG. 1 b    being a simplified stick drawing showing the force generator  26  as it has pulled the screw nut boss  22  towards the knuckle  12  to a part closed position of the mechanical finger. The screw nut boss  22  travels through the proximal element slot  42 , as it does the distance between the screw nut boss  22  and the proximal element to knuckle pivot  14  gets shorter, because the screw nut boss  22  and the rod to knuckle pivot  16  are always the same distance apart due to the length of the rod  18 , the proximal element to knuckle pivot  14  is actuated towards a closed position. The screw nut boss  22  is connected to the distal element follower aperture  47 . As the screw nut boss  22  is pulled towards the knuckle  12  the distal element follower aperture  47  is rotated around the proximal element to distal element pivot  36 . 
         [0062]      FIG. 1 c    is another schematic simplified stick drawing showing the force generator  26  as it has pulled the screw nut boss  22  towards the knuckle  12  to a fully closed position of the finger. 
         [0063]      FIG. 2 a    is a perspective view of the mechanical finger assembly shown if greater detail than  FIG. 1  in the fully open position. The frame  10  is connected to the knuckle to frame mount  48  which connects the left knuckle  52  and the right knuckle  54  to the frame  10 . The left knuckle  52  contains the left knuckle to left rod pivot  56  and the left proximal element to knuckle pivot  58 . The left rod  68  is shown coupled to and extending from the left rod to screw nut boss pivot  114  to the left knuckle to left rod pivot  56 . The left proximal element  64  is connected to the left knuckle  52  at left proximal element to knuckle pivot  58 . The left proximal element  64  is connected to the left distal element  66  at the left proximal element to distal element pivot  94 . The elastic or spring element  46  is connected in tension to the left distal element  66  and the left proximal element  64 . 
         [0064]      FIG. 2 b    is a perspective view of the mechanical finger assembly shown in the partially closed position 
         [0065]      FIG. 2 c    is a perspective view of the mechanical finger assembly shown in the fully closed position. 
         [0066]      FIG. 3 a    shows a partial sectional view of the mechanical finger. The left proximal element  64 , the left distal element  66  and the left rod  68  have been removed for clarity. Inside the left proximal element  64  and the right proximal element  72  is the force generator  26  which is connected to the screw  74 . When the force generator  26  receives a drive command it rotates to move the screw  74  in a clockwise or counter clockwise direction. The screw nut  76  is threaded onto the screw  74 . The screw nut  76  has a left screw nut boss  62  which extends through the left proximal element slot  78  (not shown). Although the left proximal element slot  78  is not shown on  FIG. 3 a , 3 b    or  3   c , that feature can be seen on  FIGS. 13 a , 13 b  and 13 c   . The right screw nut boss  82  (not shown) extends though the right proximal element slot  84  (not shown). As the left and right pivot bosses extend through the respective left and right proximal element slots, they serve to prevent the screw nut  76  from rotating inside the proximal element cavity in response to rotation of the screw  74  as the prosthesis is commanded to operate. Rotation of screw  74  in the screw nut  76  exerts a torsional force on the screw nut  76 . By preventing the screw nut  76  from rotating, the torque applied to the screw nut  76  is converted and combined with the inclined plane of the screw thread to provide an axial linear force to the screw nut boss pivot  21  (shown in  FIGS. 1 a - c   ) via the left and right boss as they extend through the left proximal element slot  78  (not show) and right proximal element slot  84  (not shown). 
         [0067]      FIG. 3 b    shows a partial view of the mechanical finger in the partially closed position with the screw nut  76  being at its middle position on the length of the screw  74 .  FIG. 3 c    shows a partial sectional view of the mechanical finger in the fully closed position with the screw nut  76  moved to a limit on screw  74  toward the motor or force generator  26 . 
         [0068]      FIG. 4 a    is a perspective view from above, of the mechanical finger.  FIG. 4 b    is an exploded view of  FIG. 4 a   . A sensor  86  is positioned in the proximal element cavity between the rear or knuckle end of the motor and the knuckle to frame mount  48 . The sensor  86  measures the longitudinal position or distance that the screw nut  76  is at or has traveled along the length of the screw  74  driven by the force generator  26 . The force generator  26  is connected to and rotates the screw  74 . 
         [0069]    As stated earlier, the screw  74  is threaded into the screw nut  76 . The screw nut  76  has a left screw nut boss  62  and a right screw nut boss  82 . These elements constitute the drive mechanism. The drive mechanism is contained inside the proximal element cavity formed by the left proximal element  64  and the right proximal element  72 . In operation, as the force generator  26  receives a command or drive signal, the screw  74  turns, the screw nut  76  is prevented from turning by the left proximal element slot  78  and the right proximal element slot  84  shown on  FIGS. 8 a  and 8 b   . The slots  78  and  84  allow a linear movement of the screw nut  76  along the threaded length of the screw  74 . 
         [0070]    With continuing reference to the exploded view of  FIG. 4 b   , the left knuckle  52  is connected to the left proximal element  64  at the left proximal element to knuckle pivot  58 . The right knuckle  54  is connected to the right proximal element  72  at the right knuckle to proximal element pivot  88  (not shown). The left knuckle  52  is connected to the right knuckle  54 . The knuckle to frame mount  48  is connected to the left knuckle  52  and right knuckle  54 . The knuckle to frame mount  48  is connected to the frame  10 . 
         [0071]    The left distal element  66  is connected to the right distal element  92 . The left distal element  66  and right distal element  92  are pivoted on the proximal element at the right proximal element to distal element pivot  96  (not shown) which is formed by the left distal element to proximal element pivot boss  126  capturing the left distal element to proximal element pivot aperture  132  (not shown), and the left proximal element to distal element pivot  94  (not shown) which is formed by the right distal element to proximal element pivot boss  128  capturing the right distal element to proximal element pivot aperture  134  (not shown). The left proximal element to distal element pivot  94  and the right proximal element to distal element pivot  96  facilitate the rotational movement of the distal elements  66 ,  92  relative to the proximal elements  64 ,  72 . 
         [0072]    The left rod  68  has rod boss  138  that captures the left knuckle rod aperture  146  to form the left knuckle to left rod pivot  56 . The right rod  98  has rod boss  139  that captures the right knuckle rod aperture  148  to form the right knuckle to rod pivot  102 . 
         [0073]    The left rod  68  has a rod aperture  136  that is received by the left screw nut boss  62 . The right rod  98  has a rod aperture  137  that receives the right screw nut boss  82 . 
         [0074]      FIG. 5 a    shows a plan view of the mechanical finger with a section line A-A and  FIG. 5 b    shows the sectional view of  FIG. 5 a    taken on section line A-A. The frame  10  is shown connected to the knuckle to frame mount  48  which is shown connected to the right knuckle  54 . The sensor  86  is depicted inside and to the rear of the force generator  26 . The microprocessor  104  is shown on top of the force generator  26 . The bearing for screw knuckle end  106  and the screw  74  is attached to the left end of the force generator  26 . The screw  74  is threaded through the screw nut  76 . A bearing for screw distal end  108  is shown that holds the distal end of the screw  74 . An elastic or spring element  46  is shown that is joined to the left proximal element  64  (not shown) and right proximal element  72 , and to the left distal element  66  (not shown) and right distal element  92 . The bearings for screw knuckle end  106  and the bearing for screw distal end  108  protect the screw  74  and the force generator  26  from radial and linear loading. 
         [0075]      FIG. 6 a    shows the left distal element  66  and the right distal element  92  with the assembly screws  112  holding the two in contact with each other to form the distal element  38 . The left distal element  66  has a left distal element flange  122 . The left distal element flange  122  has a left distal element to proximal element pivot aperture  132  and a left distal element aperture  116 . The right distal element  92  has a right distal element flange  124 . The right distal element flange  124  has a right distal element to proximal element pivot aperture  134  and a right distal element aperture  118 .  FIG. 6 b    shows an exploded view of  FIG. 6 a   . It may be possible to reverse the position and function of the left distal element aperture  116  and the right distal element aperture  118  with the left distal element to proximal element pivot aperture  132  and the right distal element to proximal element pivot aperture  134 . 
         [0076]      FIG. 7 a    shows the force generator  26  and drive mechanism assembly. The sensor  86  is connected to the force generator  26 . The force generator  26  is connected to and drives the screw  74 . The screw nut  76  is threaded onto the screw  74 . The bearing for screw knuckle end  106  and the bearing for screw distal end  108  are designed to protect the force generator  26  from axial (thrust) and radial loading.  FIG. 7 b    is an exploded perspective view of  FIG. 7 a      
         [0077]      FIG. 8 a    is a perspective view of the assembled proximal formed from a left proximal element  64  and a right proximal element  72 .  FIG. 8 b    also shows the assembly screws  112  used to couple the left and right sides to form the proximal element  24 . 
         [0078]    The left distal element to proximal element pivot boss  126  is shown above the left proximal element slot  78 . The right distal element to proximal element pivot boss  128  is shown above the right proximal element slot  84 . The left distal element to proximal element pivot boss  126  and right distal element to proximal element pivot boss  128  each respectively extend through the respective left and right distal element into proximal element pivot apertures  132 ,  134  on the respective left and right flanges  122 ,  124  of the distal element. 
         [0079]    The left distal element to proximal element pivot boss  126  with the left distal element to proximal element pivot apertures  132  (shown on  FIG. 6 . b ), and the right distal element to proximal element pivot boss  128  with the right distal element to proximal element pivot apertures  134  (shown on  FIG. 6 . b ), in combination form the proximal element to distal element pivot  36  (shown on  FIG. 1 . a ). The left proximal element  64  has a left proximal element to knuckle boss  156  that is received by a left proximal element to knuckle aperture  152  shown on  FIGS. 9 a  and 9 b   . The right proximal element  72  has a right proximal element to knuckle boss  158  (not shown) that is received by a right proximal element to knuckle aperture  154  also shown on  FIGS. 9 a  and 9 b   . The combination of left proximal element to knuckle boss  156  into the left proximal element to knuckle aperture  152  and the right proximal element to knuckle boss  158  into the right proximal element to knuckle aperture  154  form the proximal element to knuckle pivot  14 .  FIG. 8 b    shows an exploded view of  FIG. 8   a.    
         [0080]      FIG. 9 a    is a perspective view of the knuckle  12  formed from a left knuckle  52  and a right knuckle  54  pair of components. The knuckle to frame mount  48  and the frame  10  are also shown. The left knuckle  52  is joined to the right knuckle  54  with two assembly screws  112 . The knuckle to frame mount  48  is attached to the left knuckle  52  and right knuckle  54  with screws  112 . The frame  10  is attached to the knuckle to frame mount  48  with screws  112 . The left knuckle  52  has a left proximal element to knuckle aperture  152 . The right knuckle  54  has a right proximal element to knuckle aperture  154  as discussed in connection with the above discussion of  FIG. 8 a    and  FIG. 8   b.    
         [0081]      FIG. 9 b    shows an exploded view of  9   a.    
         [0082]      FIGS. 10 a -10 d    shows the left rod  68 . The left rod  68  is the same as the right rod  98  (not shown). The left rod  68  contains a rod aperture  136  that fits onto left screw nut boss  62  (not shown) to form left rod to screw nut boss pivot  114 . The right rod  98  (not shown) contains a right rod aperture  137  that fits onto right screw nut boss  82  to form right rod to screw nut boss pivot  120 . The combination of the left rod  68  which contains the left rod aperture  136  with the left screw nut boss  62  and the right rod aperture  137  with the right screw nut boss  82  form the screw nut boss pivot  21  located on the screw nut boss  22 . 
         [0083]    The left rod  68  also contains the rod boss  138 . The rod boss  138  connects the left rod  68  to the left knuckle to left rod pivot  56 . To increase efficiency the left rod  68  has a rod aperture bearing  142  inserted into the rod aperture  136 , and rod boss bearing  144  inserted onto the rod boss  138 . The right rod  98  mirrors the described arrangement of the left rod  68 . 
         [0084]    The stiffness of the rod contributes to the ability of the mechanical finger to deliver a grip that could exceed design limits. It may be possible to design the rods so as to experience distortion when a design limit is exceeded so as to preclude damage to the structure elements. One possible design embodiment for this purpose could be to design the rods to have a corrugated or curved feature fabricated into the surface of the rod, or to design the rod to have a spring characteristic. The combination of the left rod boss  138  with the left knuckle rod aperture  146  along with the combination of an identical right rod boss  139  (not shown) with the right knuckle rod aperture  148  form the rod to knuckle pivot  16  shown in  FIGS. 1 a   - 1   c.    
         [0085]      FIG. 11 a    is a side view of the screw nut  76 .  FIG. 11 b    is a front view of the screw nut  76 .  FIG. 11 c    is an exploded view of the screw nut  76  showing the left screw nut boss  62  and the right screw nut boss  82  with sleeve bearings ready for installation on the bosses and aligned on each of the bosses. 
         [0086]      FIG. 11 d    is a perspective view of the screw nut  76 , with sleeve bearings on the left and right screw nut boss. The left screw nut boss  62  and the right screw nut boss  82 , each with sleeve bearings installed are received by the respective proximal element slots  78 ,  84  (not shown), and the outer surface of the bearings are sized to ride in the proximal element slots. 
         [0087]      FIG. 11 e    is an exploded view of the screw nut  76  with the left screw nut boss  62  and the right screw nut boss  82 , each being ready to receive a bushing that is stopped by the edge of an earlier sleeve bearing. 
         [0088]      FIG. 11 f    is a perspective view showing the screw nut assembly ready for assembly, the bushing on each of the bosses  62 ,  82  receiving the respective distal element aperture for screw nut boss left and right side  116 ,  118  (not shown). The sleeves and bearings are added to space the distal element aperture for screw nut boss left and right side from the respective outer surface of the proximal element  24  and add an increase in efficiency between the left screw nut boss  62  and the right screw nut boss  82  and the distal element aperture left and right side  116 ,  118 . 
         [0089]      FIG. 12 a    is a side view of a single elastic or spring element  46 , and  FIG. 12 b    is a perspective view of a pair of elastic or spring elements  46 . 
         [0090]      FIG. 13 a    is a partial perspective view of the distal end of the left proximal element  64 , the right proximal element  72  being partially unseen behind the left side. The left and right sides are assembled together with the screw  74  appearing in  FIG. 13 c   . As shown in  FIG. 13 a   , as the mechanical finger is fully opened, the left screw nut boss  62  is at the distal end of the left proximal element slot  78 . 
         [0091]      FIG. 13 b    is a partial perspective view of the left proximal element  64  and the right proximal element  72  behind the surface, the two being assembled together with the screw  74  and screw nut  76  in the half way closed position. 
         [0092]      FIG. 13 c    a partial perspective view of the left proximal element  64  and the right proximal element  72  assembled together with the screw  74  and screw nut  76  of the mechanical finger being in the fully closed position. 
         [0093]      FIG. 14 a    shows a partial view of the proximal element to distal element joint with the finger in a fully opened configuration. The left screw nut boss  62  is in the lower part of the left distal element aperture  116  to the left of the left proximal element to distal element pivot  94 . 
         [0094]      FIG. 14 b    shows that the left screw nut boss  62  has moved approximately half way through its actuation travel. The left distal element  66  is pulled by the left screw nut boss  62  in a counter clockwise rotation towards the knuckle  12 . As the left screw nut boss  62  moves from the position shown in  FIG. 14 a   , to  FIG. 14 b    and then to  FIG. 14 c    within the left proximal element slot  78  (not shown), the left screw nut boss  62  applies a force to the edge of the left distal element aperture  116  that results in a torque applied to the left distal element  66  forcing it to pivot and rotate in a counter clockwise rotation around the left proximal element to distal element pivot  94 . The left screw nut boss  62  touches the inner surface or perimeter of the left distal element aperture  116  with a sliding or rolling surface on a fixed slot surface only traversing an arc path along the inner surface of the left distal element aperture  116 . The arc movement of the left screw nut boss  62  is accommodated by the left distal element aperture  116  as the left screw nut boss  62  travels upwards in the left distal element aperture  116  towards the left proximal element to distal element pivot  94 . In  FIG. 14 c    the finger is fully closed; the left screw nut boss  62  can be seen sitting in the lower part of the left distal element aperture  116  away from the left proximal element to distal element pivot  94 . 
         [0095]    It will be understood that the right distal element  92  has the same relationship and movement with the right screw nut boss  82  (not shown) as the left distal element  66  has with the left screw nut boss  62 .  FIG. 14 a -14 c    also shows the elastic or spring element  46  which is attached and connects the left proximal element  64  and the right proximal element  72  to the left distal element  66  and the right distal element  92 . The elastic or spring element  46  is in tension, so when the power is interrupted or paused, the elastic or spring element  46  together with the resistance in the force generator  26  and the drive mechanism operate to resist and prevent the mechanical finger from opening. If the mechanical finger is holding an item at the time of the interruption, the item held will remain secured in the grip of the mechanical finger, or fingers as the case may be. 
         [0096]      FIGS. 15 a -15 c    are distinguished from  FIGS. 14 a -14 c    by showing the addition of left rod  68  in the  FIGS. 15 a -15 c    series.  FIG. 15 a    shows a partial view of the left proximal element  64  and the right proximal element  72  receding into the image. The left proximal element  64  is assembled together with the left rod  68 . The left rod  68  is connected to the left screw nut boss  62  (not shown) at the left rod to screw nut boss pivot  114 .  FIG. 15 a    shows the mechanical finger in a fully open position.  15   b  shows the mechanical finger in a partially closed position and  FIG. 15 c    shows the mechanical finger in a fully closed position. 
         [0097]      FIG. 16 a    shows the proximal element to distal element pivot with the distal element having an alternative embodiment—the distal element has a more elongated left distal element aperture  116  and right distal element aperture  118  (not shown). The left screw nut boss  62  and the right screw nut boss  82  (not shown) sit inside a more elongated left distal element aperture  116  and the right distal element aperture  118  (not shown).  FIG. 16 b    shows the left distal element  66  and the right distal element  92  (not shown) receiving an unexpected load and being pushed downwards by the force. Since the left distal element aperture  116  and right distal element aperture  118  (not shown) are more elongated the left distal element  66  and the right distal element  92  (not shown) are able to be pushed downwards, this can be used as a feature to protective the mechanical finger from accidental external shock. 
         [0098]    While certain specific relationships, materials and other parameters have been detailed in the above description of a preferred embodiment, those can be varied, where suitable, with similar results. Other applications and variations of the present invention will occur to those skilled in the art upon reading the present disclosure. Those variations are also intended to be included within the scope of this invention as defined in the appended claims. 
       APPENDIX 
     List of Parts 
       [0000]    
       
           10 —Frame 
           12 —Knuckle 
           14 —First pivot—Proximal element to knuckle pivot 
           16 —Second pivot—Rod to knuckle pivot 
           18 —Rod 
           21 —Third pivot—Screw nut boss pivot 
           22 —Screw nut boss 
           24 —Proximal element 
           26 —Force generator 
           28 —Battery 
           32 —Control sensor 
           34 —Processor 
           36 —Fourth pivot—Proximal element to distal element pivot 
           38 —Distal element 
           42 —Proximal element slot 
           44 —Distal element pivot aperture 
           45 —Distal element follower 
           46 —Elastic or spring element 
           47 —Distal element follower aperture 
           48 —Knuckle to frame mount 
           52 —Left knuckle 
           54 —Right knuckle 
           56 —Left knuckle to left rod pivot 
           58 —Left proximal element to knuckle pivot 
           62 —Left screw nut boss 
           64 —Left proximal element 
           66 —Left distal element 
           68 —Left rod 
           72 —Right proximal element 
           74 —Screw 
           76 —Screw nut 
           78 —Left proximal element slot 
           82 —Right screw nut boss 
           84 —Right proximal element slot 
           86 —Sensor 
           88 —Right knuckle to proximal element pivot 
           92 —Right distal element 
           94 —Left proximal element to distal element pivot 
           96 —Right proximal element to distal element pivot 
           98 —Right rod 
           102 —Right knuckle to rod pivot 
           104 —Microprocessor 
           106 —Bearing for screw knuckle end 
           108 —Bearing for screw distal end 
           112 —Assembly screws 
           114 —Left rod to screw nut boss pivot 
           116 —Left distal element aperture 
           118 —Right distal element aperture 
           120 —Right rod to screw nut boss pivot 
           122 —Left distal element flange 
           124 —Right distal element flange 
           126 —Left distal element to proximal element pivot boss 
           128 —Right distal element to proximal element pivot boss 
           132 —Left distal element to proximal element pivot aperture 
           134 —Right distal element to proximal element pivot aperture 
           136 —Left rod aperture 
           137 —Right rod aperture 
           138 —Left rod boss 
           139 —Right rod boss 
           142 —Rod aperture bearing 
           144 —Rod boss bearing 
           146 —Left knuckle rod aperture 
           148 —Right knuckle rod aperture 
           152 —Left proximal element to knuckle aperture 
           154 —Right proximal element to knuckle aperture 
           156 —Left proximal element to knuckle boss 
           158 —Right proximal element to knuckle boss