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.

Natural organisms have a unique property not yet available in robotics, i.e., a self-healing (SH) ability. This powerful biological healing function has inspired chemists to impart similar properties to synthetic materials to create “SH materials.” Recent developments in SH polymers led us to investigate the potential of using these materials in robotics. This paper presents an innovative approach of using SH polymers, based on the reversible Diels-Alder (DA) reaction, in a compliant actuator. Using DA polymers, a sacrificial SH mechanical fuse (SH-MF) is designed, developed, and validated by placing it in a cable-driven robotic system. The fuse is designed as weakest element and will sacrificially fail if a damaging overload occurs, protecting the compliant element and other components of the system. The experimental results showed that this SH-MF could be healed at a relatively low temperature, recovering the initial mechanical properties. This first working prototype indicates the feasibility to use SH materials in robotics. “SH robotics” will lead to more sustainable and lighter systems, and eventually to more efficient designs.

Last 15 years, a wide range of self-healing (SH) materials has been developed and recently these materials are increasingly used in applications in multiple fields, like the automotive industry and aerospace. However, so far this material technology is not yet explored in robotics. The introduction of these materials in robotics will potentially reduce the over-dimensioning of current robotic systems, leading to lighter systems and eventually to more efficient designs. Compliant elements used in next generation soft robots, can be constructed from available SH-materials, making them able to autonomously heal cuts and perforations caused by sharp objects in unstructured environments. In addition, the use of SH-materials will have a beneficial impact on the life span of robotic components, reducing the required maintenance drastically. This paper presents the innovative concept of implementing a SH-mechanism in compliant actuators, using dynamic covalent polymer network systems based on the reversible Diels-Alder (DA) reaction. For two entirely different compliant actuators, a series elastic actuator (SEA) and a soft pneumatic actuator (SPA), an analysis is presented on the integration of the DA-polymers in the actuator designs. For both actuator types, a prototype was designed, developed and validated.