ZERO STIFFNESS IN BELLOW-TYPE SOFT PNEUMATIC ACTUATORS FOR MODAL ANALYSIS OF FLEXIBLE AIRCRAFT WINGS

Modern aircraft designs with high aspect ratio wings pose challenges in accurately determining vibrational modes due to the increased flexibility of their wings. To accurately represent the large deformations occurring during flight in experimental modal analysis, actuators of low stiffness are needed, leading to the exploration of quasi-zero-stiffness vibration isolators. Such vibration isolators, combining positive and negative stiffness elements, lack the adaptability needed for varying wing load conditions. This study explores bellow-type soft pneumatic actuators, fabricated using 3D printing for iterative design and parameter studies, as a potential solution. Initial experiments and simulations focused on the actuator stiffness for different geometric parameters and pressures. While simulations suggested that the occurrence of zero stiffness was primarily influenced by geometric parameters like the radius-to-height ratio, experimental results did not align with these findings, revealing discrepancies due to unmodeled boundary conditions. This misalignment highlighted the challenges in achieving the desired zero-stiffness characteristic in practical applications. In conclusion, This study reveals that current bellow-type actuators fall short of the near-zero stiffness required for accurate modal analysis in flexible aircraft structures. Despite promising simulation results, experimental discrepancies highlight the need for improved designs and testing methods. Future research, potentially exploring rolling lobe actuators and refining 3D printing techniques, remains crucial in the ongoing quest for an ideal actuator in this domain.