Inflatable Snapping Metamaterials for Next Generation Soft Machines

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Soft machines are mechanical devices made of soft materials and perform functions through their bodily deformation. Their benefits over traditional rigid counterparts are typically reported in terms of interaction safety, adaptability and low-cost fabrication. Soft machines can be driven by elastic inflatable actuators, which exhibit a variety of motions according to their design. Similarly, flexible mechanical metamaterials are designed to achieve desired mechanical responses, including complex nonlinear effects such as reversible snap-through instabilities. Indeed, a metamaterial is defined as an artificial material that exhibits special properties beyond the ones of its constituents. This project aims at creating a new family of soft machines by designing and fabricating inflatable snapping actuators that harness the nonlinear response of architected metamaterials. Thanks to the high tunability of the mechanical metamaterial response, novel functionalities will be encoded in the structure, enabling next generation soft machines with simplified control and embodied intelligence. In this proposal, three main objectives are targeted. The first objective is to design and fabricate an inflatable actuator with a nonlinear pressure-volume curve that allows snap-through phenomenon. As a simple inflatable shell has a linear monotonic pressure-volume response (if there are no ballooning effects), the snap-through will be induced solely by the metamaterial architecture. The second objective is to develop a methodology to design simplified control schemes by exploiting the snapping response of the actuators. This approach is named “morphological control”, as it makes use of the physical properties of the system to achieve a control task. An array of interconnected actuators will be modelled as a nonlinear fluidic network. An algorithm will be developed to invert the nonlinear fluidic network equations and obtain the system parameters based on the desired response, e.g., a specific sequenced pattern of actuation. Lastly, the previous concepts will be applied to design and fabricate a bi-modal soft robotic demonstrator that can locomote on land and water. The soft robot envisioned in this project will have a single pressure input for all the actuators and the sequences that create the locomotion patterns will be, therefore, morphologically controlled. The new designs and control principles envisaged in this proposal will be paramount to enable next generation multifunctional soft machines with higher levels of embodied intelligence.