Final Words

Working from a previously-synthesized design concept, my research focused on the optimization of a spark-ignition, internal-combustion actuator, intended to provide direct actuation for ankle plantarflexion in an active ankle-foot orthosis (AAFO). Optimization of the cylinder design was focused on meeting pressure and force loading requirements, through the gas-power cycle. Both, the designable (dynamic design space) and non-designable (fixed) geometries were generated using SolidWorks®, and were then imported into solidThinking Inspire® for optimization. The fixed geometry was used for load applications, and to establish certain necessary design features. Dynamic design space was created around the fixed geometry, within which the software algorithm performed its morphological optimization process, dependent on the connections and setup specified. In order to establish the loads for the setup, it was necessary to correlate the gait cycle to the power cycle, and determine the pressure-volume relationship for the design. The desired result was a combustion-cylinder design optimized for the projected loading during the power cycle required to provide full gait assistance. However, an optimized result was not finalized. This was attributed to difficulties with the optimization software, but it is unclear as to what the exact root cause of the failed optimization attempts was.

   If this project is picked back up in the future, an optimization procedure will need to be validated. Additionally a real gas cycle could be developed to verify pressure loadings applied, the fixed geometry could be sophisticated, and the running gait cycle could be considered. It was desirable to consider the running gait cycle this summer, but insufficient quantitative data was found in order to do so.  

   A future related project could address the thermal-management requirements in the cylinder optimization. These include, but are not limited to, external surface temperature, as mandated by the Food and Drug Administration (FDA), flame quenching considerations, and further material considerations. 

Research Paper