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LOADS IN A PROSTHETIC PYLONTharshan Vaithianathan; M Eng Sc. (Monash University)
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This study used strain gauges to find the axial, bending and torsionloads of a prosthetic lower limb pylon . A realistic measurement of the forces transferred to the stump via the prosthetic socket needs to be known. As there are only rigid connections between the socket and the pylon, a method to measure these forces was devised concentrating on strain measurement at the pylon. Using a strain gauge direct connect card (5508BG), which provides the signal conditioning, ten strain gauges were configured on a standard 30mm aluminium prosthetic pylon. |
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The configuration was designed to provide:
A single 30 way ribbon cable connected the strain gauges to the data acquisition card. Real time data analysis was obtained using LabTech Notebook software, which includes software programmable gains and the acquired data was displayed in graphical format. The data can also be stored in ASCII format for further analysis.A data logger would provide a more mobile system, removing the limitations of the cable.
This system was fitted to a 290mm long pylon. It is possible to mount these strain gauges on a shorter pylon where the minimum length is approximately 50mm between the pylon adaptors. After calibration the pylon was fitted onto a trans-tibial endoskeletal prosthesis. Initial results compared well with literature. It was also tested on the REHABTech fatigue machine which mimics normal gait.
The forces measured can be used to obtain the following: shock absorption properties of prosthetic feet component forces in relation to proposed ISO standard forces while running. It will also provide the actual forces at the distal end of the socket, useful for FEA (Finite Element Analysis)of the socket. The advantage of considering strain gauges instead of load cells, is that there is no need to modify the prosthesis, while the properties of the pylon remain unchanged. Load cells will however be investigated.
