Abstract
Different tasks and conditions in gait call for different stiffness of prosthetic foot devices. The following work presents a case study on design modifications of a prosthetic foot, aimed at variable stiffness of the device. The objective is a proof-of-concept, achieved by simulating the modifications using finite element modeling. Design changes include the addition of a controlled damping element, connected both in parallel and series to a system of springs. The aim is to change the stiffness of the device under dynamic loading, by applying a high damping constant, approaching force coupling for the given boundary conditions. The dynamic modelling simulates mechanical test methods used to measure load response in full roll-over of prosthetic feet. Activation of the element during loading of the foot justifies the damped effect. As damping is in contrast to the main design objectives of energy return in prosthetic feet, it is considered important to quantify the dissipated energy in such an element. Our design case shows that the introduction of a damping element, with a high damping constant, can increase the overall rotational stiffness of the device by 50%. Given a large enough damping coefficient, the energy dissipation in the active element is about 20% of maximum strain energy.
Highlights
Energy storage and return (ESR) prosthetic feet serve as designated spring systems, storing energy in mid-stance of gait, that again is released for propulsion of the foot in late stance [1,2]
Stiffness of the foot contributes to this roll-over, affecting the forces and moments exerted on the residual limb, and users’ whole body kinematics [4]
Mahmoodi et al [19] used finite element analysis (FEA) to optimize design parameters of three types of prosthetic feet to estimate optimal stiffness based on gait analysis data, such as ground reaction forces and roll-over shape
Summary
Energy storage and return (ESR) prosthetic feet serve as designated spring systems, storing energy in mid-stance of gait, that again is released for propulsion of the foot in late stance [1,2]. Published work on the application of FEA in prosthetic foot design has focused on investigating structural characteristics of components, rather than function These works show FEA of individual mechanical components for stress analysis to models of the whole prosthetic, focusing on the force response in the anisotropic carbon fiber material. Mahmoodi et al [19] used FEA to optimize design parameters of three types of prosthetic feet to estimate optimal stiffness based on gait analysis data, such as ground reaction forces and roll-over shape. A new joint, restrained with a spring and damper element, is defined in the modified model This will result in a more compliant force response of the foot, as shown in previous work [29]. The strain energy is analyzed, in order to quantify the dissipation of using damped force coupling for change in stiffness
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