In nature, repeated base units produce handed structures that selectively bond to make rigid or compliant materials. Auxetic tilings are scale-independent frameworks made from repeated unit cells that expand under tension. We discovered how to produce handedness in auxetic unit cells that shear as they expand by changing the symmetries and alignments of auxetic tilings. Using the symmetry and alignment rules that we developed, we made handed shearing auxetics that tile planes, cylinders, and spheres. By compositing the handed shearing auxetics in a manner inspired by keratin and collagen, we produce both compliant structures that expand while twisting and deployable structures that can rigidly lock. This work opens up new possibilities in designing chemical frameworks, medical devices like stents, robotic systems, and deployable engineering structures.
Abstract-In this paper, we explore a new class of electric motor-driven compliant actuators based on handed shearing auxetic cylinders. This technique combines the benefits of compliant bodies from soft robotic actuators with the simplicity of direct coupling to electric motors. We demonstrate the effectiveness of this technique by creating linear actuators, a four degree-of-freedom robotic platform, and a soft robotic gripper. We compare the soft robotic gripper against a state of the art pneumatic soft gripper, finding similar grasping performance in a significantly smaller and more energy-efficient package.
Electrically-mediated actuation schemes offer great promise beyond popular pneumatic and suction based ones in soft robotics. However, they often rely on bespoke materials and manufacturing approaches that constrain design flexibility and widespread adoption. Following the recent introduction of a class of architected materials called handed shearing auxetics (HSAs), we present a 3D printing method for rapidly fabricating HSAs and HSA-based soft robots that can be directly driven by servo motors. To date, HSA fabrication has been limited to the laser cutting of extruded teflon tubes. Our work expands the HSA materials palette to include flexible and elastomeric polyurethanes. Herein, we investigate the influence of material composition and geometry on printed HSAs' mechanical behavior. In addition to individual HSA performance, we evaluate printed HSAs in two soft robotic systems -four degree-of-freedom (DoF) platforms and soft grippers -to confirm that printed HSAs perform similarly to the original teflon HSA designs. Finally, we demonstrate new soft robotic capabilities with 3D printed HSAs, including fully 3D printed HSA fingers, higher force generation in multi-DoF devices, and demonstrations of soft grippers with internal HSA endoskeletons. We anticipate our methods will expedite the design and integration of novel HSAs in electrically-driven soft robots and facilitate broader adoption of HSAs in the field.
Single-stream recycling is currently an extremely labor intensive process due to the need for manual object sorting. Soft robotics offers a natural solution as compliant robots require less computation to plan paths and grasp objects in a cluttered environment. However, most soft robots are not robust enough to handle the many sharp objects present in a recycling facility. In this work, we present a soft sensorized robotic gripper which is fully electrically driven and can detect the difference between paper, metal and plastic. By combining handed shearing auxetics with high deformation capacitive pressure and strain sensors, we present a new puncture resistant soft robotic gripper. Our materials classifier has 85% accuracy with a stationary gripper and 63% accuracy in a simulated recycling pipeline. This classifier works over a variety of objects, including those that would fool a purely vision-based system.
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