Deformable high energy storage tension spring
AssigneeEcole Polythechnique
InventorsRoland Dore, Gilbert Drouin
Life of this patent
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Abstract
A tension spring capable of large elastic deformation and having a high resistance to breakage and particularly, but not exclusively, for use as an artificial prosthetic ligament. The spring comprises an elongate elastic core having a low modulus of elasticity and defining opposed ends. A tensionable wrapping of thread having a high resistance to breakage is disposed in contact about the core to compress the core and to cause it to elongate axially upon opposite relative axial displacement of opposed ends of the wrapping secured to traction means.
Claims14
An artificial prosthetic ligament capable of large elastic deformation and high resistance to breakage comprising an elongate elastic core having a low modulus of elasticity and opposed ends, a tensionable wrapping formed of threads having a large resistance to breakage is provided in contact about said core, said wrapping being constituted by at least two windings of helically wound thread having large resistance to breakage and a high modulus of elasticity as compared to that of the core, said windings being disposed in alternate opposed directions to one another and having substantially the same helix angle, said core being elongated axially by compression force applied by said wrapping caused by opposite relative axial displacement of opposed ends of said wrapping secured to traction means, said elongation being determined by the mathematical expression:
- ##EQU8## where .nu. is the Poisson ratio of the material, .DELTA.L is the elongation of the prosthesis, E.sub.f is the Young's modulus of the fiber material, D is the external diameter of the core, D.sub.i is the internal diameter of the core, .alpha. is the helix angle, L is the length of the prosthesis, E(p) is the elastic modulus function of the core, n is the number of threads, .epsilon. is the axial strain for a given length L, F is the tensile force, and d is the thread diameter.
A method of making an artificial prosthetic ligament comprising the steps of (i) providing an elastic core having a low modulus of elasticity, (ii) helically winding at least two windings of a thread having a large resistance to breakage about said core, said windings extending in opposed directions with their thread windings disposed at substantially the same helix angle, said windings constituting a wrapping having opposed ends, (iii) displacing said opposed ends in opposite axial directions by traction means for compressing said core to cause it to elongate, the elongation being determined by the mathematical expression:
- ##EQU9## where .nu. is the Poisson ratio of the material, .DELTA.L is the elongation of the prosthesis, E.sub.f is the Young's modulus of the fiber material, D is the external diameter of the core, D.sub.i is the internal diameter of the core, .alpha. is the helix angle, L is the length of the prosthesis, E(p) is the elastic modulus function of the core, n is the number of threads, .epsilon. is the axial strain for a given length L, F is the tensile force, and d is the thread diameter.
A tension spring capable of large elastic deformation and high resistance to breakage comprising an elastic core having a low modulus of elasticity and opposed ends, a tensionable wrapping formed of threads having a large resistance to breakage is provided in contact about said core to compress said core between its opposed ends and to cause it to elongate axially upon opposite relative axial displacement of opposed ends of said wrapping secured to traction means, said wrapping is constituted by at least two windings of helically wound thread having a large resistance to breakage and a high modulus of elasticity as compared to that of the core, said windings being disposed in alternate opposed directions to one another and having substantially the same helix angle, said helix angle being selected to achieve a predetermined axial deformation of said core when said relative displacement occurs, said axial elongation of said core being determined by the mathematical expression:
- ##EQU10## where .nu. is the Poisson ratio of the material, .DELTA.L is the elongation of the prosthesis, E.sub.f is the Young's modulus of the fiber material, D is the external diameter of the core, D.sub.i is the internal diameter of the core, .alpha. is the helix angle, L is the length of the prosthesis, E(p) is the elastic modulus function of the core, n is the number of threads, .epsilon. is the axial strain for a given length L, F is the tensile force, and d is the thread diameter.
Dependencies are inferred from the claim text.