Method and apparatus for improved stiffness in the linkage assembly of a flexible arm

Abstract

The invention includes linkage assemblies comprising coupled links with metallic contact surfaces with improved stiffness. The inventors found significant mechanical problems with all previous descriptions of metallic contact links sufficient to preclude their commercial use. These metallic contact links are a significant improvement over existing plastic ball and metal joint, or all plastic beads as found in the prior art. The invention includes methods providing these links and high friction couplings between them, as well as the linkage assemblies and flexible arms resulting from these processes.

1 . A flexible, articulated arm comprising: 
 a first link having a first concave contact surface, a first convex contact surface and a first cable opening passing through said first concave contact surface and said first convex contact surface,    a second link having a second concave contact surface, a second convex contact surface and a second cable opening passing through said second concave contact surface and said second convex contact surface,    a third link having a third concave contact surface, a third convex contact surface and a third cable opening passing through said third concave contact surface and said third convex contact surface,    and a tension cable extending through said first, second and third cable openings,    wherein said first concave contact surface engages said second convex contact surface,    wherein said second concave contact surface engages said third convex contact surface,    wherein said first and third links are formed of a first material and said second link is formed of a second, different material.    
     
     
         2 . The flexible, articulated arm of  claim 1 , wherein said first and third links are formed of a single material.  
     
     
         3 . The flexible, articulated arm of  claim 1 , wherein said second link is formed of a single material.  
     
     
         4 . The flexible, articulated arm of  claim 1 , wherein said first and third links are formed entirely of a first material and said second link is entirely formed of a second, different material.  
     
     
         5 . The flexible, articulated arm of  claim 1 , wherein said first material is a coating on a body of said first and third links.  
     
     
         6 . The flexible, articulated arm of  claim 1 , wherein said second material is a coating on a body of said second link.  
     
     
         7 . The flexible, articulated arm of  claim 6 , wherein said first material is a coating on a body of said first and third links.  
     
     
         8 . The flexible, articulated arm of  claim 1 , wherein said first, second and third links are formed of metallic compounds.  
     
     
         9 . The flexible, articulated arm of  claim 1 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.3.  
     
     
         10 . The flexible, articulated arm of  claim 1 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.35.  
     
     
         11 . The flexible, articulated arm of  claim 1 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.375.  
     
     
         12 . The flexible, articulated arm of  claim 1 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.3875.  
     
     
         13 . The flexible, articulated arm of  claim 1 , further comprising a plurality of additional links having a shape and composition matching said first link and wherein said tension cable extends through said plurality of additional links.  
     
     
         14 . The flexible, articulated arm of  claim 1 , wherein said first material is formed of an alloy containing an element selected from the group of elements consisting of nickel, titanium, iron and copper.  
     
     
         15 . The flexible, articulated arm of  claim 1 , wherein said first material is stainless steel.  
     
     
         16 . The flexible, articulated arm of  claim 15 , wherein said second material is a nickel-titanium alloy.  
     
     
         17 . The flexible, articulated arm of  claim 1 , wherein said first material is a nickel-titanium alloy.  
     
     
         18 . A flexible, articulated arm comprising: 
 a first link having a first contact surface, a second contact surface and a first cable opening passing therethrough,    a second link having a third contact surface, a fourth contact surface and a second cable opening passing therethrough,    a third link having a fifth contact surface, a sixth contact surface and a third cable opening passing therethrough,    wherein said second contact surface engages said third contact surface creating a first contact region,    wherein said second contact surface is formed of a first material and said third contact surface is formed of a second, different material,    wherein said fourth contact surface engages said fifth contact surface creating a second contact region,    wherein one of said fourth contact surface and said fifth contact surface is formed of said first material, and one of said fourth contact surface and said fifth contact surface is formed of said second material,    and wherein a coefficient of friction between said first and second material is at least 0.3,    and a tension cable extending through said first, second and third cable openings.    
     
     
         19 . The flexible, articulated arm of  claim 18 , wherein said coefficient of friction is at least 0.35.  
     
     
         20 . The flexible, articulated arm of  claim 18 , wherein said coefficient of friction is at least 0.375.  
     
     
         21 . The flexible, articulated arm of  claim 18 , wherein said coefficient of friction is at least 0.3875.  
     
     
         22 . A flexible, articulated arm comprising: 
 a first link having a first concave contact surface, a first convex contact surface and a first cable opening passing through said first concave contact surface and said first convex contact surface,    a second link having a second concave contact surface, a second convex contact surface and a second cable opening passing through said second concave contact surface and said second convex contact surface,    a third link having a third concave contact surface, a third convex contact surface and a third cable opening passing through said third concave contact surface and said third convex contact surface,    and a tension cable extending through said first, second and third cable openings,    wherein said first concave contact surface engages said second convex contact surface,    wherein said second concave contact surface engages said third convex contact surface,    and wherein said first, second and third concave contact surfaces are formed of a first material and said first, second and third convex contact surfaces are formed of a second, different material.    
     
     
         23 . The flexible, articulated arm of  claim 22 , wherein each of said first, second and third links have a body and said first, second and third concave contact surfaces are formed by a coating on said body.  
     
     
         24 . The flexible, articulated arm of  claim 22 , wherein each of said first, second and third links have a body and said first, second and third convex contact surfaces are formed by a coating on said body.  
     
     
         25 . The flexible, articulated arm of  claim 24 , wherein said first, second and third concave contact surfaces are formed by a second different coating on said body.  
     
     
         26 . The flexible, articulated arm of  claim 22 , wherein said first, second and third links are formed of metallic compounds.  
     
     
         27 . The flexible, articulated arm of  claim 22 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.3.  
     
     
         28 . The flexible, articulated arm of  claim 22 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.35.  
     
     
         29 . The flexible, articulated arm of  claim 22 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.375.  
     
     
         30 . The flexible, articulated arm of  claim 22 , wherein a coefficient of friction exists between said first material and said second material and said coefficient of friction is at least 0.3875.  
     
     
         31 . The flexible, articulated arm of  claim 22 , further comprising a plurality of additional links having a shape and composition matching said first link and wherein said tension cable extends through said plurality of additional links.  
     
     
         32 . The flexible, articulated arm of  claim 22 , wherein said first material is formed of an alloy containing an element selected from the group of elements consisting of nickel, titanium, iron and copper.  
     
     
         33 . The flexible, articulated arm of  claim 22 , wherein said first material is stainless steel.  
     
     
         34 . The flexible, articulated arm of  claim 33 , wherein said second material is a nickel-titanium alloy.  
     
     
         35 . The flexible, articulated arm of  claim 22 , wherein said first material is a nickel-titanium alloy.  
     
     
         36 . A flexible arm linkage apparatus provided with a tensioning cable, comprising: 
 a first link forming a first contact surface composed of a first contact material and approximating a partial convex surface supporting said tensioning cable passing through said first contact surface;    a second link forming a second contact surface composed of a second contact material and approximating a partial concave surface supporting said tensioning cable passing through said second contact surface; and    a high friction coupling between said first link and said second link is created by said first contact surface contacting said second contact surface when induced by said tensioning cable;    wherein said first contact material is distinct from said second contact material;    wherein each of said first contact material and said second contact material is primarily composed of a respective metallic compound;    wherein said first contact surface composed of said first contact material contacting said second contact surface composed of said second contact material has a friction coefficient greater than each member of the collection comprising: 
 a friction coefficient value of 0.3;  
 said first contact surface composed of said first contact material contacting  
   said second contact surface composed of said first contact material; and said first contact surface composed of said second contact material contacting said second contact surface composed of said second contact material.    
     
     
         37 . A flexible arm linkage apparatus provided with a tensioning cable, comprising: 
 a first link forming a first contact surface composed of a first contact material and approximating a first partial convex surface supporting said tensioning cable passing through said first contact surface;    a second link forming a second contact surface composed of a second contact material and approximating a first partial concave surface supporting said tensioning cable passing through said second contact surface; and    a high friction coupling between said first link and said second link is created by said first contact surface contacting said second contact surface when induced by said tensioning cable;    wherein each of said first contact material and said second contact material is primarily composed of a respective metallic compound;    wherein said first contact surface contacting said second contact surface when induced by said tensioning cable further provides a maximal static friction combined with a maximal kinetic friction between said first link and said second link through a contact region;    wherein said contact region is smaller than a maximal contact region obtained from altering at least one member of the collection comprising said first contact surface and said second contact surface; and    wherein said first contact surface composed of said first contact material contacting said second contact surface composed of said second contact material has a friction coefficient greater than a friction coefficient value of 0.3.