Dynamic Finite-Element analysis of a soft bending actuator

Abstract

Compliance is both a blessing and a curse in the soft robotics field. Increased flexibility comes with serious challenges in the dynamic modeling of compliant manipulators. Soft bending actuators, with their widespread application in rehabilitative, locomotive, and manipulative robotics, are no exception. Dynamic modeling of these actuators is specifically important, as it directly affects the design criteria. In other words, the effect of geometrical features on different aspects of dynamic response such as natural frequencies or magnitude and phase responses should be investigated. Since analytical modeling of their dynamic response is extremely challenging due to the high nonlinearity of both their geometrical and material features, the Finite-Element method is regarded as a proper technique to model these actuators and gain more insight into their dynamical behavior. This study presents a Finite-Element model to describe the dynamic behavior of a pneumatically-driven soft bending actuator, including an analysis of its natural frequencies and response shape. Since inflation of the actuator impacts its structural stiffness and geometrical domain, its effect is studied on the first five natural frequencies by modeling it as a prestress. The proposed model has been scripted and analyzed in ABAQUS, regarding its hyperelastic material behavior, and then is verified experimentally by comparing the numerical analysis data with the results obtained from the bending behavior of a fabricated prototype in different frequencies. In addition to a favorable match between model and test data, a design platform is presented regarding the effect of changes in length and different thicknesses on the bending angle and curvature. Moreover, it is discovered that the geometrical features of the actuator do not endanger the assumption that its bending shape has a constant curvature. In fact, this assumption is only valid in low-frequency applications.