Fluidic artificial muscles (FAMs) are a form of soft actuator that have been applied to an expanding number of applications, due to their unique characteristics such as low weight, simple construction, inherent compliance, and high specific force and specific work capabilities. With energy sourced from a pressurized fluid, contractile FAMs provide a uniaxial contractile force, while their morphing geometry allows them to contract in length. In a design environment where actuators have tight spatial requirements and must provide precise force and position control, it is becoming more important than ever to have accurate mathematical representations of FAM actuation behavior and geometric characteristics to ensure their successful implementation. However, geometric models and force analyses for FAMs are still relatively crude. Geometric models of FAMs assume a cylindrical geometry, the accuracy of which is suspect because there are no documented methods for effectively measuring FAM shape. Actuation force analyses are also relatively inaccurate unless they are adjusted to fit to experimental response data. Research has continually pursued methods of improving the predictive performance of these analyses by investigating the complex working mechanisms of FAMs.

This research improves these analyses by first, making improvements to the experimental characterization of a FAM's actuation response, and then using the more comprehensive data results to test long-held modeling assumptions. A quantitative method of measuring FAM geometry is developed that provides 0.004 in/pixel resolution measurements throughout a characterization test. These measurements are then used to test common assumptions that serve as sources of uncertainty: the cylindrical approximation of FAM geometry, and assumption that the FAM's braid is inelastic. Once these sources of modeling error are removed, the model's performance is then tested for potential improvements. Results from this research showed that the cylindrical approximation of the FAM's geometry resulted in overestimations of the FAM's average diameter by 4.7%, and underestimations of the FAM's force by as much as 37%. The inelastic braid assumption resulted in a maximum 4% underestimation of average diameter and a subsequent 5% overestimation in force, while the use of softer braid materials was found to have the potential for much larger effects (30% underestimation in diameter, 70% overestimation in force). With subsequent adjustments made to the force model, the model was able to achieve a fit with a mean error of only 2.8 lbf (0.3% of maximum force).

This research demonstrates improvements to the characterization of a FAM's actuation response, and the use of this new data to improve the fidelity of existing FAM models. The demonstrated characterization methods can be used to clearly define a FAM's geometry to aid in the effective design and implementation of a FAM-actuated mechanism, or to serve as a foundation for further investigation into the working mechanisms and development of FAMs.