Variable stiffness system based on rheology properties of shear thickening fluid

The unique rheological properties of discontinuous shear thickening fluids (STF) have been employed in various engineering applications in recent years. In a commercial aspect, this has most notably been body armor and protective equipment, but also specialized smart structures in damping and force-coupling applications. The topic of this work is the application of STF in a translational element for an articulating prosthetic foot. Connected in series and parallel to a spring system, the element can be used to affect the force transfer within the system and thereby influence the stiffness of the prosthetic foot dynamically over the gait cycle. The device described in this work is a STF filled piston/cylinder design. The objective is a velocity dependent force response over the translational motion. Ranging from dampened, compliant deflection at low velocity, to efficient force transfer (coupling) for energy storage and return in the spring system at higher speed. The rapid viscosity increase in the STF at a critical shear rate is used to produce a stepwise force response, thereby enabling adaptive response of the foot for different walking speeds and other various tasks, such as standing up from a seated position. The adaptive response results in a greater range of motion with easier rollover through stance phase for slow movement without sacrificing the energy return needed in faster walking.