Method for design and manufacture of compliant prosthetic foot
A compliant prosthetic foot is designed and fabricated by combining a compliant mechanism optimization technique with a calculation of low leg trajectory error under a reference loading condition. The compliant mechanism optimization technique includes a set of determinants for the compliant prosthetic foot. An optimized set of determinants of the compliant prosthetic foot is formed that minimizes the lower leg trajectory error relative to a target kinematic data set. The compliant prosthetic foot is then fabricated in conformance with the optimized set of determinants.
1. A method for fabricating a compliant prosthetic foot, comprising:
a) combining a compliant mechanism optimization technique that includes a set of determinants for a parametric curve defining a shape of a compliant prosthetic foot with a calculation of lower leg trajectory error under a reference loading condition;
b) forming an optimized set of determinants of the compliant prosthetic foot that minimizes the lower leg trajectory error relative to a target kinematic data set; and
c) fabricating the compliant prosthetic foot in conformance with the optimized set of determinants, the compliant prosthetic foot comprising a singular body configured to elastically deform to achieve a desired output motion.
2. The method of claim 1 , wherein the target kinematic data set includes a physiological data set.
3. The method of claim 1 , wherein the compliant mechanism optimization technique optimizes a set of determinants for a prosthetic foot that is compliant along its entire length.
4. The method of claim 3 , wherein the compliant mechanism optimization technique includes a parameterization step, wherein wide Bezier curve parameters are incorporated into a genetic algorithm to find a set of parameters that creates a foot that minimizes lower leg trajectory error.
5. The method of claim 4 , wherein the compliant mechanism optimization technique employs a cubic curve defined by relative positions of at least two control points.
6. The method of claim 5 , wherein the cubic curve is defined by relative positions of four control points.
7. The method of claim 4 , wherein the compliant mechanism optimization technique employs a width of the Bezier curve as a variable, wherein the width is a function of control circles.
8. The method of claim 7 , wherein the width of the Bezier curve is defined as a function of diameters of four control circles.
9. The method of claim 1 , wherein the compliant mechanism optimization technique is combined with the lower leg trajectory error calculation by setting design parameters of the compliant prosthetic foot to not exceed a predefined design space.
10. The method of claim 9 , further including the step of setting the design parameters to limit the design of the compliant prosthetic foot to configurations that are realizable.
11. The method of claim 10 , wherein the set of determinants of the compliant prosthetic foot is set by finite element analysis.
12. The method of claim 11 , wherein the finite element analysis includes setting time intervals within a gait cycle and conducting the finite element analysis for each time interval.
13. The method of claim 12 , wherein the time intervals extend from foot flat.
14. The method of claim 13 , wherein the compliant mechanism optimization technique includes employing a heel component in combination with a wide Bezier curve.
15. The method of claim 14 , wherein the time intervals extend from early stance plantar flexion.
16. The method of claim 1 , wherein the target kinematic data set is a physiological data set obtained from a subject for whom the compliant prosthetic foot is being fabricated.
17. The method of claim 1 , wherein the target kinematic data set is a physiological data set obtained from an able-bodied subject with the same body size and mass as the subject for whom the compliant prosthetic foot is being fabricated.
18. The method of claim 1 , wherein the target kinematic data set is a physiological data set scaled from an able-bodied subject to adjust for differences in body size and mass compared to the subject for whom the compliant prosthetic foot is being fabricated.
19. The method of claim 1 , wherein the target kinematic data set is obtained by at least one member of the group consisting of simulation, measurement of a subject, measurement from a population of subjects, and scaling in magnitude from a subject(s) of a different body size and weight.
20. The method of claim 1 , wherein the compliant prosthetic foot is fabricated by at least one method selected from the group consisting of: machining; three-dimensional printing; a layup method; a water jet method; additive fabrication;
subtractive fabrication; lamination; composite manufacture; injection molding; carbon fiber fabrication; extrusion; casting; molding; co-molding; carving; and vulcanization.
21. The method of claim 1 , wherein the compliant prosthetic foot is fabricated of at least one member of the group consisting of: nylon 6/6; carbon fiber;
fiber glass; spring steel; titanium; plastic; an alloy of metals; a polymer; a composite; a resin; a thermoplastic; laminate; a rubber; an elastomer; a non-viscoelastic material; a viscoelastic material; and wood.
22. A compliant prosthetic foot fabricated by a process comprising:
a) combining a compliant mechanism optimization technique that includes a set of determinants for a parametric curve defining a shape of a compliant prosthetic foot with a calculation of lower leg trajectory error under a reference loading condition;
b) forming an optimized set of determinants of the compliant prosthetic foot that minimizes the lower leg trajectory error relative to a target kinematic data set; and
c) fabricating the compliant prosthetic foot in conformance with the optimized set of determinants, the compliant prosthetic foot comprising a singular body configured to elastically deform to achieve a desired output motion.