Design Analysis of Power Harvesting Passive Ankle Foot Orthoses

Abstract

Stroke may cause lots of sequelae Among the sequelae drop foot may influence the gait control gait pattern stability and working performance on people with stroke Ankle-foot orthoses (AFOs) are usually prescribed for people with stroke Currently the commercially available power harvesting AFO could not only help patients solve the drop foot problem but also store and release more energy than traditional AFO This AFO could store and release more energy because of its geometry and material of the footplate This energy restoration could help people with stroke propulsion There are a frontal lift design and the arch design on power harvesting AFO When people used AFO with these two designs during walking the footplate would deform And this deformation would help AFO store energy However there still few of studies discussed the effects on the different frontal lift angles and arch design This study aims to design a AFO based on the commercially available power harvesting AFO with different frontal lift angles and different arch height in the footplate In addition this study changed the geometry of footplate to find the optimal design This study used SolidWorks 2016 to build the power harvesting AFO (PH-AFO) model There are three parameters in this study including frontal lift angle arch height and the materials of footplate There are five different frontal lift angles including 28 2o 22 56o 16 92o 11 28o and 5 64o There are five different arch heights in this study including 9 74mm 8 11mm 6 49mm 4 87mm and 3 25mm Two different material which are titanium and carbon fiber composite were used in this study This study imported the PH-AFO model into ANSYS Workbench to do the finite element analysis (FEA) In the FEA data of stroke patients was used in this study to simulate the stroke patients’ gait PH-AFO with higher frontal lift angle stored more strain energy There was no increased or decreased tendency as the arch height decreased in the strain energy result but maximum strain energy occurred at lowest arch height (3 25mm) The energy stored in arch design might help patients do heel-off PH-AFO with frontal lift angle 28 2o and arch height 3 25mm with the material of titanium stored the maximum strain energy in the simulation result The return energy could assist the patient in push-off PH-AFO with frontal lift angle 28 2o and arch height 3 25mm with the material of titanium also contributed most in ankle moment The more energy released from AFO the less effort patients make Bregman et al made a carbon fiber AFO (CFOs) with carbon fiber spring connecting the calf part and footplate part [51] In their study the percentage of CFOs contribution in ankle moment was 52%; while the percentage of PH-AFO contribution in ankle moment was 43% with the material of titanium and 40% with the material of carbon fiber composite The contribution of CFOs came from the deformation of the carbon fiber spring; while the contribution of PH-AFO came from the deformation of the footplate Patients could choose the AFO with different contribution depended on their own recovery progress Future study might consider combine these two features together to get the higher AFO contribution and stored energy

Date of Award	2019
Original language	English
Supervisor	Fong-chin Su (Supervisor)