Topology optimized multi-material self-healing actuator with reduced out of plane deformation

Recent advances in soft robotics in academia have led to the adoption of soft grippers in industrial settings. Due to their soft bending actuators, these grippers can handle delicate objects with great care. However, due to their flexibility, the actuators are prone to out-of-plane deformations upon asymmetric loading. These undesired deformations lead to reduced grasp performance and may cause instability or failure of the grip. While the state-of-the-art contributions describe complex designs to limit those deformations, this work focuses on a complementary path investigating the material distribution. In this paper, a novel bending actuator is developed with improved out-of-plane deformation resistance by optimizing the material distribution in multi-material designs composed of two polymers with different mechanical properties. This is made possible by the strong interfacial strength of Diels-Alder chemical bonds in the used polymers, which have a self-healing capability. A Solid Isotropic Material with Penalization (SIMP) topology optimization is performed to increase the out-of-plane resistance. The actuator is simulated using FEA COMSOL in which the (hyper) elastic materials are simulated by Mooney-Rivlin models, fitted on experimental uniaxial tensile test data. This multi-material actuator and a reference single material actuator were manufactured and modeled. Via experimental characterization and validation in FEA simulations, it is shown that the actuator out-of-plane stiffness, characterized by the in-plane bending angle and out-of-plane bending angle, can be increased by an optimized multi-material composition, without changing the geometrical shape of the actuator.