Fish Cells as a new metamaterial with zero Poisson’s ratio in two planar directions is introduced with application in morphing aircraft skin. In order to tailor the design of this metamaterial for arbitrary loadings, equivalent elastic properties of the Fish Cells metamaterial are derived and analyzed using analytical and numerical methods. The admissible range of geometric parameters is presented and variation of elastic properties with parameters is studied. The effective elastic modulus of the metamaterial is derived analytically and verified with finite element models. The in-plane and transverse shear modulus of the metamaterial are evaluated using finite element analysis where accurate periodic boundary conditions for in-plane shear loading are investigated. The lower and upper bounds of the transverse shear modulus are derived based on strain and complementary energy relations which are verified with finite element results. As zero Poisson’s ratio behavior of the Fish Cells topology is proved, derivative geometries from this topology with zero Poisson’s ratio behavior are also presented.
Widespread adoption of soft robotic technologies is held back by the limitations of existing soft robotic actuators. One cause of the limited performance of soft actuators is their uni-polar stroke, which means only part of the workcycle is powered. In this work, we introduce RoboHeart, a bi-directional compliant smart actuator. RoboHeart consists of two spring-steel strips covered with PVC insulation, pre-bent into a heart shape and is driven by dielectrophoretic zipping. Here, we perform isotonic and isometric characterisation of RoboHeart performance, demonstrating work output of 17 mJ (expansion) and 18 mJ (contraction) and power of 1.5 mW (expansion) and 2 mW (contraction). We then confirm the practical application of RoboHeart by demonstrating a 10-RoboHeart ring configuration capable of gripping a range of objects as they are lifted. We also demonstrate bidirectional control of actuation using three separate control channels. We believe that RoboHeart represents a step towards highperformance soft actuators and technologies.
The high potential impact of soft robotics is hampered by a lack of actuators that combine high-force, high-work and high-power capabilities, limiting application in real-world problems. Typically, soft actuators are tuned to an application by gearing -for example, trading power for strain. An example of a recently developed soft-actuator which exploits such gearing is the dielectrophoretic liquid zipping (DLZ) actuator. DLZs can produce large strains (>99%) and power densities comparable to biological muscles, but cannot achieve both in a single actuator. In this work, we introduce a muscle-mimetic DLZ ratcheting actuator (DLZ-R) that allows multiple DLZ-R heads to operate in parallel, thereby increasing force output without sacrificing stroke or power. We first characterise the effect of geometry on the performance of a 1-head DLZ-R, before demonstrating that the force, work, and power output of the DLZ-R scale linearly with the number of active DLZ heads. Next, we investigate the relationship between driving frequency and power output. Finally, we demonstrate a 12-head DLZ ratchet. We believe the DLZ-R represents a step towards soft actuators that can provide both high-work and high-power and the widespread use of soft technologies.
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