Tailoring Stress-Strain Curves of Flexible Snapping Mechanical Metamaterial for On-Demand Mechanical Responses via Data-Driven Inverse Design.

By incorporating soft materials into the architecture, flexible mechanical metamaterials enable promising applications, e.g., energy modulation, and shape morphing, with a well-controllable mechanical response, but suffer from spatial and temporal programmability towards higher-level mechanical intelligence. One feasible solution is to introduce snapping structures and then tune their responses by accurately tailoring the stress-strain curves. However, owing to the strongly coupled nonlinearity of structural deformation and material constitutive model, it is difficult to deduce their stress-strain curves using conventional ways. Here, a machine learning pipeline is trained with the finite element analysis data that considers those strongly coupled nonlinearities to accurately tailor the stress-strain curves of snapping metamaterialfor on-demand mechanical response with an accuracy of 97.41%, conforming well to experiment. Utilizing the established approach, the energy absorption efficiency of the snapping-metamaterial-based device can be tuned within the accessible range to realize different rebound heights of a falling ball, and soft actuators can be spatially and temporally programmed to achieve synchronous and sequential actuation with a single energy input. Purely relying on structure designs, the accurately tailored metamaterials increase the devices' tunability/programmability. Such an approach can potentially extend to similar nonlinear scenarios towards predictable or intelligent mechanical responses.

Synergistical Mechanical Design and Function Integration for Insect-Scale On-Demand Configurable Multifunctional Soft Magnetic Robots.

Meso- or micro-scale(or insect-scale) robots that are capable of realizing flexible locomotion and/or carrying on complex tasks in a remotely controllable manner hold great promise in diverse fields, such as biomedical applications, unknown environment exploration, in situ operation in confined spaces, and so on. However, the existing design and implementation approaches for such multifunctional, on-demand configurable insect-scale robots are often focusing on their actuation or locomotion, while matched design and implementation with synergistic actuation and function modules under large deformation targeting varying task/target demands are rarely investigated. In this study, through systematical investigations on synergistical mechanical design and function integration, we developed a matched design and implementation method for constructing multifunctional, on-demand configurable insect-scale soft magnetic robots. Based on such a method, we report a simple approach to construct soft magnetic robots by assembling various modules from the standard part library together. Moreover, diverse soft magnetic robots with desirable motion and function can be (re)configured. Finally, we demonstrated (re)configurable soft magnetic robots shifting into different modes to adapt and respond to varying scenarios. The customizable physical realization of complex soft robots with desirable actuation and diverse functions can pave a new way for constructing more sophisticated insect-scale soft machines that can be applied to practical applications soon.

A Dual-Modal Hybrid Gripper with Wide Tunable Contact Stiffness Range and High Compliance for Adaptive and Wide-Range Grasping Objects with Diverse Fragilities.

The difficulties of traditional rigid/soft grippers in meeting the increasing performance expectations (e.g., high grasping adaptability and wide graspable objects range) of a single robotic gripper have given birth to numerous soft-rigid coupling grippers with promising performance. However, it is still hard for these hybrid grippers to adaptively grasp various objects with diverse fragilities intact, such as incense ash and orange, due to their limited contact stiffness adjustable range and compliance. To solve these challenging issues, herein, we propose a dual-modal hybrid gripper, whose fingers contain a detachable elastomer-coated flexible sheet that is restrained by a moving frame as a teardrop shape. The gripper's two modes switched by controlling the moving frame position can selectively highlight the low contact stiffness and excellent compliance of the teardrop-shaped flexible sheets and the high contact stiffness of the moving frames. Moreover, the contact stiffness of the teardrop-shaped sheets can be wide-range adjusted by online controlling the moving frame position and offline replacing the sheets with different thicknesses. The compliance of the teardrop-shaped sheets also proves to be excellent compared with an Ecoflex 10 fingertip with the same profile. Such a gripper with wide-range tunable contact stiffness and high compliance demonstrates excellent grasping adaptability (e.g., it can safely grasp several fragile strawberries with a maximum size difference of 18 mm, a strawberry with a left/right offset of 3 cm, and a strawberry in two different lying poses) and wide-range graspable objects (from 0.1 g super fragile cigarette ashes to 5.1 kg dumbbell).

Bioinspired Multimodal Multipose Hybrid Fingers for Wide-Range Force, Compliant, and Stable Grasping.

The increasing demand for grasping diverse objects in unstructured environments poses severe challenges to the existing soft/rigid robotic fingers due to the issues in balancing force, compliance, and stability, and hence has given birth to several hybrid designs. These hybrid designs utilize the advantages of rigid and soft structures and show better performance, but they are still suffering from narrow output force range, limited compliance, and rarely reported stability. Owing to its rigid-soft coupling structure with flexible switched multiple poses, human finger, as an excellent hybrid design, shows wide-range output force, excellent compliance, and stability. Inspired by human finger, we propose a hybrid finger with multiple modes and poses, coupled by a soft actuator (SA) and a rigid actuator (RA) in parallel. The multiple actuation modes formed by a pneumatic-based rigid-soft collaborative strategy can selectively enable the RA's high force and SA's softness, whereas the multiple poses derived from the specially designed underactuated RA skeleton can be flexibly switched with tasks, thus achieving high compliance. Such hybrid fingers also proved to be highly stable under external stimuli or gravity. Furthermore, we modularize and configure these fingers into a series of grippers with excellent grasping performance, for example, wide graspable object range (diverse from 0.1 g potato chips to 27 kg dumbbells for a 420 g two-finger gripper), high compliance (tolerate objects with 94% gripper span size and 4 cm offset), and high stability. Our study highlights the potential of fusing rigid-soft technologies for robot development, and potentially impacts future bionics and high-performance robot development.

Fabrication and Functionality Integration Technologies for Small-Scale Soft Robots.

Small-scale soft robots are attracting increasing interest for visible and potential applications owing to their safety and tolerance resulting from their intrinsic soft bodies or compliant structures. However, it is not sufficient that the soft bodies merely provide support or system protection. More importantly, to meet the increasing demands of controllable operation and real-time feedback in unstructured/complicated scenarios, these robots are required to perform simplex and multimodal functionalities for sensing, communicating, and interacting with external environments during large or dynamic deformation with the risk of mismatch or delamination. Challenges are encountered during fabrication and integration, including the selection and fabrication of composite/materials and structures, integration of active/passive functional modules with robust interfaces, particularly with highly deformable soft/stretchable bodies. Here, methods and strategies of fabricating structural soft bodies and integrating them with functional modules for developing small-scale soft robots are investigated. Utilizing templating, 3D printing, transfer printing, and swelling, small-scale soft robots can be endowed with several perceptual capabilities corresponding to diverse stimulus, such as light, heat, magnetism, and force. The integration of sensing and functionalities effectively enhances the agility, adaptability, and universality of soft robots when applied in various fields, including smart manufacturing, medical surgery, biomimetics, and other interdisciplinary sciences.

Stiffness Preprogrammable Soft Bending Pneumatic Actuators for High-Efficient, Conformal Operation.

Soft pneumatic actuators (SPAs) are extensively investigated due to their simple control strategies for producing sophisticated motions. However, the motions or operations of homogeneous SPAs show obvious limitations in some varying curvature interaction scenarios because of the profile mismatch of homogeneous SPAs and specific interacted objects. Herein, a stiffness preprogrammable soft pneumatic actuator (SPSPA) is proposed by discretely presetting gradient geometrical or materials distributions. Through finite element analysis and experimental validation, a mathematical model of behavior prediction of SPSPA was built to relate the geometrical parameters/materials with its morphing behaviors, making it possible to reversely obtain designed parameters. This design strategy enables conformal and efficient interaction in some curvature varying scenarios. Specifically, higher effective contact area, perimeter utilization ratio, and conformal ability can be obtained while interacting with those inhomogeneous curvature objects, for example, more than 434.7% improvement in contact area rates and 12.5% enhancement in perimeter utilization ratios toward a typical equilateral triangle object. Further, a serial of SPSPAs that have conformal grasping/interactive capability, better contact sensing behaviors were demonstrated. For example, an SPSPA and an SPSP robot were demonstrated, which showed better kinetic, kinematic characterizations and sensing capability compared with the homogeneous one while coming across varying curvature objects. Moreover, underactuated finger rehabilitation SPSPAs were demonstrated with customized profiles and coupled joint motion. This customized scheme can be potentially used in those specific-purposed, single, and repetitive application scenarios where varying curvature, conformal and efficient interaction are needed.

Anisotropic Shear-Sensitive Tactile Sensors with Programmable Elastomers for Robotic Manipulations.

High-performance tactile sensors are urgently demanded in various intensive interactive scenarios, e.g., texture detection, robotic interaction with fragile objects, and motion direction recognition, where dynamic conditions are involved with complex tangential forces or vibrations. Although many microstructured/porous sensors can perceive tangential forces, their isotropic structures that lack programmability lead them to be incapable of sensing the direction of forces and restrain their tunability for complex situations, e.g., a wide sensing range for large forces and high sensitivity for gentle forces. Here, by tuning the programmable microstructures (microcolumns and microfilms) of an elastomeric active layer, we propose a simple principle to flexibly tune the shear sensitivity of an anisotropic porous sensor and bring a 10-fold distinction of anisotropy with a wide range of shear sensitivity (from 0.07 to 0.7 N-1). The fabricated tactile sensors can be used in various robotic manipulations resiliently, for instance, morphology and topology identification of curved surfaces, delicate interactive manipulations, and recognizing the relative motion of two contacting objects. Our work introduces a simple and effective strategy for tailoring flexible shear-sensitive sensors for diverse dexterous robotic manipulations during complex interactions.