Date of Award


Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

Committee Member

Suyi Li, Committee Chair

Committee Member

Lonny Thompson

Committee Member

Ian Walker


Plants have unorthodox motion. The seed appendage of Stork's Bill plant (Erodium Gruinum) moves in such a way due to two physiological features. Plant cells are reinforced by cellulose fibers distributed in a tilted helix pattern — helixes that are tilted at a certain angle with respect to the longitudinal axis of the cell. Another feature is dehydration of cell tissue which causes volumetric shrinking. Due to the cellulose-fibers and dehydration of cell tissue, the seed appendage can coil and uncoil via a combination of twisting and bending. Coiling motion can be quite useful for robotic manipulation and locomotion purposes. This research proposes and investigates a novel actuator that is inspired and derived from the unique cell wall architecture in the seed appendage of Stork's Bill plant (Erodium Gruinum). This study aims to examine the coiling and uncoiling motion of a soft pneumatic actuator reinforced with tilted helix fibers. Detailed design and fabrication processes are developed to create a fully functional soft actuator which represents the experimental model. Since the material is "soft", hyperelastic models are used and compared to the nominal stress-strain data from the uniaxial test to determine which material model best represents the material and used for the FEA model. With both FEA and experimental models created, the setup of both models is developed to gather data for results. From the results, the standard and tilted helix fiber reinforcements show different actuator motion as a tilted helix actuator primarily produce bending in addition to twisting, thus producing coiling. Quantitatively, the FEA and experimental are not in agreement. However, qualitatively, both models show similar coiling motion. Parametric studies are performed by changing the tilt angle of the fiber to show the effectiveness of coiling. The FEA models are validated qualitatively by the experimental models. In conclusion, larger tilt angles produce more bending motion, thus less twisting motion is shown which causes the actuator to primarily coil outward than produce coils. Lower tilt angles produce less bending motion, thus more twisting motion is shown which causes the actuator to primarily coil more frequently and coil outward to a lesser extent. The results coincide with the study, as soft actuators with a tilted helix fiber reinforcement can primarily produce bending in addition to twisting which results in the coiling motion. With these results, a new family of soft actuators with unique motion can be explored and developed, which is appealing for soft robot application.