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Design of multi-material soft pneumatic modules

Modularized soft pneumatic actuators (SPAs) can flexibly achieve various actuation modes by using a series of modules. However, existing modules are generally composed of single materials, and may perform limited actuation modes. To achieve an enlarged space for desirable and manually-tunable actuation modes, this study creates multi-material soft modules. To incorporate highly nonlinear responses of the soft modular bodies into the design process, a topology optimization method is firstly developed to generate feasible modular configurations by determining the best distribution of the two materials, and then the parameterized models are built, which are inspired by the optimized solutions. Two types of modules are designed. One type acquires target bending curvatures by distributing the two materials in a top-bottom asymmetric form, and the other type attains the maximal twisting capability by embedding helical hard material into the soft base. Furthermore, various modularized SPAs are made by assembling the designed modules in different sequence, and they are able to achieve a variety of actuation modes. By using one of the modularized SPA, a soft gripper is designed to accomplish a complex grasping task. The real samples of the designed modules and SPAs are made by using a multi-step casting approach. Both numerical and experiment results verify the performance of the multi-material soft modules, the modularized SPAs and the soft gripper.