A novel torsional spring design for knee prostheses and exoskeletons

Abstract

In this thesis, a novel torsion spring design for use in knee prostheses and exoskeletons is presented and analyzed. The planar spring design features an outer hub and an inner hub, which are connected by slender beams and store torsion energy in beam bending. The beams are fixed to the outer hub on one end and attached to the inner hub by a pin and slot on the other. The modeled spring design is capable of deflecting ± [pi]/6 radians, higher than any existing planar torsion spring designs, and is capable of providing 100 N-m of torque. The maraging steel spring is predicted to have a total diameter of 0.112 meters, width of 0.005 meters, and mass of 98 grams. With this form factor, the planar spring design provides a more compact alternative to elastic elements currently used in series elastic actuators. From the presented models, the design dimensions, material, and slot geometry can be parametrized to design springs that meet specific requirements for different applications. In addition to quantifying performance, the models presented provide the foundation for further weight, efficiency, and performance optimization.