Adaptive Self-Sealing Suction-Based Soft Robotic Gripper

Octopus-Inspired Underwater Soft Robotic Gripper with Crawling and Swimming Capabilities

Can a robotic gripper only operate when attached to a robotic arm? The application space of the traditional gripper is limited by the robotic arm. Giving robot grippers the ability to move will expand their range of applications. Inspired by rich behavioral repertoire observed in octopus, we implement an integrated multifunctional soft robotic gripper with 6 independently controlled Arms. It can execute 8 different gripping actions for different objects, such as irregular rigid/soft objects, elongated objects with arbitrary orientation, and plane/curved objects with larger sizes than the grippers. Moreover, the soft gripper can realize omnidirectional crawling and swimming by itself. The soft gripper can perform highly integrated tasks of releasing, crawling, swimming, grasping, and retrieving objects in a confined underwater environment. Experimental results demonstrate that the integrated capabilities of multimodal adaptive grasping and omnidirectional motions enable dexterous manipulations that traditional robotic arms cannot achieve. The soft gripper may apply to highly integrated and labor-intensive tasks in unstructured underwater environments, including ocean litter collecting, capture fishery, and archeological exploration.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Classification and Evaluation of Octopus-Inspired Suction Cups for Soft Continuum Robots

The emergence of the field of soft robotics has led to an interest in suction cups as auxiliary structures on soft continuum arms to support the execution of manipulation tasks. This application poses demanding requirements on suction cups with respect to sensorization, adhesion under non-ideal contact conditions, and integration into fully soft systems. The octopus can serve as an important source of inspiration for addressing these challenges. This review aims to accelerate research in octopus-inspired suction cups by providing a detailed analysis of the octopus sucker, determining meaningful performance metrics for suction cups on the basis of this analysis, and evaluating the state-of-the-art in suction cups according to these performance metrics. In total, 47 records describing suction cups are found, classified according to the deployed actuation method, and evaluated on performance metrics reflecting the level of sensorization, adhesion, and integration. Despite significant advances in recent years, the octopus sucker outperforms all suction cups on all performance metrics. The realization of high resolution tactile sensing in suction cups and the integration of such sensorized suction cups in soft continuum structures are identified as two major hurdles toward the realization of octopus-inspired manipulation strategies in soft continuum robot arms.

Bioinspired multiscale adaptive suction on complex dry surfaces enhanced by regulated water secretion

Suction is a highly evolved biological adhesion strategy for soft-body organisms to achieve strong grasping on various objects. Biological suckers can adaptively attach to dry complex surfaces such as rocks and shells, which are extremely challenging for current artificial suction cups. Although the adaptive suction of biological suckers is believed to be the result of their soft body's mechanical deformation, some studies imply that in-sucker mucus secretion may be another critical factor in helping attach to complex surfaces, thanks to its high viscosity. Inspired by the combined action of biological suckers' soft bodies and mucus secretion, we propose a multiscale suction mechanism which successfully achieves strong adaptive suction on dry complex surfaces which are both highly curved and rough, such as a stone. The proposed multiscale suction mechanism is an organic combination of mechanical conformation and regulated water seal. Multilayer soft materials first generate a rough mechanical conformation to the substrate, reducing leaking apertures to micrometres (~10 µm). The remaining micron-sized apertures are then sealed by regulated water secretion from an artificial fluidic system based on the physical model, thereby the suction cup achieves long suction longevity on complex surfaces but minimal overflow. We discuss its physical principles and demonstrate its practical application as a robotic gripper on a wide range of complex dry surfaces. We believe the presented multiscale adaptive suction mechanism is a powerful unique adaptive suction strategy which may be instrumental in the development of versatile soft adhesion.

Constrained Origami Artificial Muscle-Driven Robotic Manipulator Capable of Coordinating Twisting and Grasping Motions for Object Manipulation

Grasping and twisting motions are vital when manipulating objects due to their fundamental role in enabling precision, adaptability, and effective interaction. However, few studies in soft robotics exploiting artificial muscles have achieved object manipulation in situ through the coordination of twisting and grasping motions akin to our forearm and hand's capabilities. Especially, when using the same artificial muscle module to achieve these two motions will greatly simplify the manufacturing and control complexity. Here, we introduce identical origami artificial muscle modules (OAMMs) subjected to distinct end constraints into the design of the robotic manipulator, allowing it to achieve independent grasping and twisting motions to achieve effective, precise object manipulation. Applying different end constraints to the identical OAMMs yields distinct motions at their ends, where utilizing a fixed end and a sliding end realizes pure translation, while opting for a fixed end and a rotating end enables pure rotation. The differentially constrained OAMMs then serve as soft actuators for the manipulator's torsional mechanism and grasping mechanism to accomplish independent, controllable twisting and grasping motions. The coordination of twisting and grasping motions finally enables the manipulator to complete various tasks, including installing a light bubble, pouring the water from a lidded bottle into a cup, and sorting and stacking puzzle blocks. Our study pioneers the utilization of OAMMs for precise and versatile object manipulation through the coordination of independent twisting and grasping motions.

Variable stiffness soft robotic gripper: design, development, and prospects

The advent of variable stiffness soft robotic grippers furnishes a conduit for exploration and manipulation within uncharted, non-structured environments. The paper provides a comprehensive review of the necessary technologies for the configuration design of soft robotic grippers with variable stiffness, serving as a reference for innovative gripper design. The design of variable stiffness soft robotic grippers typically encompasses the design of soft robotic grippers and variable stiffness modules. To adapt to unfamiliar environments and grasp unknown objects, a categorization and discussion have been undertaken based on the contact and motion manifestations between the gripper and the things across various dimensions: points contact, lines contact, surfaces contact, and full-bodies contact, elucidating the advantages and characteristics of each gripping type. Furthermore, when designing soft robotic grippers, we must consider the effectiveness of object grasping methods but also the applicability of the actuation in the target environment. The actuation is the propelling force behind the gripping motion, holding utmost significance in shaping the structure of the gripper. Given the challenge of matching the actuation of robotic grippers with the target scenario, we reviewed the actuation of soft robotic grippers. We analyzed the strengths and limitations of various soft actuation, providing insights into the actuation design for soft robotic grippers. As a crucial technique for variable stiffness soft robotic grippers, variable stiffness technology can effectively address issues such as poor load-bearing capacity and instability caused by the softness of materials. Through a retrospective analysis of variable stiffness theory, we comprehensively introduce the development of variable stiffness theory in soft robotic grippers and showcase the application of variable stiffness grasping technology through specific case studies. Finally, we discuss the future prospects of variable stiffness grasping robots from several perspectives of applications and technologies.

Perceptual Soft End-Effectors for Future Unmanned Agriculture

As consumers demand ever-higher quality standards for agricultural products, the inspection of such goods has become an integral component of the agricultural production process. Unfortunately, traditional testing methods necessitate the deployment of numerous bulky machines and cannot accurately determine the quality of produce prior to harvest. In recent years, with the advancement of soft robot technology, stretchable electronic technology, and material science, integrating flexible plant wearable sensors on soft end-effectors has been considered an attractive solution to these problems. This paper critically reviews soft end-effectors, selecting the appropriate drive mode according to the challenges and application scenarios in agriculture: electrically driven, fluid power, and smart material actuators. In addition, a presentation of various sensors installed on soft end-effectors specifically designed for agricultural applications is provided. These sensors include strain, temperature, humidity, and chemical sensors. Lastly, an in-depth analysis is conducted on the significance of implementing soft end-effectors in agriculture as well as the potential opportunities and challenges that will arise in the future.

Angle-programmed tendril-like trajectories enable a multifunctional gripper with ultradelicacy, ultrastrength, and ultraprecision

Achieving multicapability in a single soft gripper for handling ultrasoft, ultrathin, and ultraheavy objects is challenging due to the tradeoff between compliance, strength, and precision. Here, combining experiments, theory, and simulation, we report utilizing angle-programmed tendril-like grasping trajectories for an ultragentle yet ultrastrong and ultraprecise gripper. The single gripper can delicately grasp fragile liquids with minimal contact pressure (0.05 kPa), lift objects 16,000 times its own weight, and precisely grasp ultrathin, flexible objects like 4-μm-thick sheets and 2-μm-diameter microfibers on flat surfaces, all with a high success rate. Its scalable and material-independent design allows for biodegradable noninvasive grippers made from natural leaves. Explicitly controlled trajectories facilitate its integration with robotic arms and prostheses for challenging tasks, including picking grapes, opening zippers, folding clothes, and turning pages. This work showcases soft grippers excelling in extreme scenarios with potential applications in agriculture, food processing, prosthesis, biomedicine, minimally invasive surgeries, and deep-sea exploration.

A bioinspired stiffness tunable sucker for passive adaptation and firm attachment to angular substrates

The ability to adapt and conform to angular and uneven surfaces improves the suction cup's performance in grasping and manipulation. However, in most cases, the adaptation costs lack of required stiffness for manipulation after surface attachment; thus, the ideal scenario is to have compliance during adaptation and stiffness after attachment to the surface. Inspired by the capability of stiffness regulation in octopus suction cup, this article presents a suction cup that adapts to steep angular surfaces due to compliance and has high stiffness after attachment. In this design, the stiffness after attachment is provided by using granular jamming as vacuum driven stiffness modulation. Thus, the design is composed of a conventional active suction pad connected to a granular stalk, emulating a hinge behavior during adaptation and creating high stiffness by jamming granular particles driven by the same vacuum as the suction pad. During the experiment, the suction cup can adapt to angles up to 85° with a force lower than 0.5 N. We also investigated the effect of granular stalk's length on the adaptation and how this design performs compared to passive adaptation without stiffness modulation.

Versatile Adhesion-Based Gripping via an Unstructured Variable Stiffness Membrane

Reversible and variable dry adhesion is a promising approach for versatile robotic grasping. Variable stiffness materials with a modulus that can be tuned using an external stimulus offer a unique approach to realize dynamic control of adhesion. In this study, an unstructured shape memory polymer (SMP) membrane with variable stiffness is used to pick-and-place three-dimensional objects. The variable stiffness of the SMP allows the membrane to conform to and make good contact with objects of various shapes in its soft state and then achieve high adhesive load capacity by switching to the stiff state. Release of objects is realized by switching to the soft state. The ratio between the high-adhesion and low-adhesion state is demonstrated to be >2000 on a curved substrate and ∼115 on a flat substrate. This gripper exhibits no adhesion in the unactivated state and maintains adhesion passively once actuation is complete.

Soft Microdenticles on Artificial Octopus Sucker Enable Extraordinary Adaptability and Wet Adhesion on Diverse Nonflat Surfaces

Bioinspired soft devices, which possess high adaptability to targeted objects, provide promising solutions for a variety of industrial and medical applications. However, achieving stable and switchable attachment to objects with curved, rough, and irregular surfaces remains difficult, particularly in dry and underwater environments. Here, a highly adaptive soft microstructured switchable adhesion device is presented, which is inspired by the geometric and material characteristics of the tiny denticles on the surface of an octopus sucker. The contact interface of the artificial octopus sucker (AOS) is imprinted with soft, microscale denticles that interact adaptably with highly rough or curved surfaces. Robust and controllable attachment of the AOS with soft microdenticles (AOS-sm) to dry and wet surfaces with diverse morphologies is achieved, allowing conformal attachment on curved and soft objects with high roughness. In addition, AOS-sms assembled with an octopus-arm-inspired soft actuator demonstrate reliable grasping and the transport of complex polyhedrons, rough objects, and soft, delicate, slippery biological samples.

Glowing Sucker Octopus (Stauroteuthis syrtensis)-Inspired Soft Robotic Gripper for Underwater Self-Adaptive Grasping and Sensing

A soft gripper inspired by the glowing sucker octopus (Stauroteuthis syrtensis)' highly evolved grasping capability enabled by the umbrella-shaped dorsal and ventral membrane between each arm is presented here, comprising of a 3D-printed linkage mechanism used to actuate a modular mold silicone-casting soft suction disc to deform. The soft gripper grasp can lift objects using the suction generated by the pump in the soft disc. Moreover, the protruded funnel-shaped end of the deformed suctorial mouth can adapt to smooth and rough surfaces. Furthermore, when the gripper contacts the submerged target objects in a turbid environment, local suctorial mouth arrays on the suction disc are locked, causing the variable flow inside them, which can be detected as a tactile perception signal to the target objects instead of visual perception. Aided by the 3D-printed linkage mechanism, the soft gripper can grasp objects of different shapes and dimensions, including flat objects, objects beyond the grasping range, irregular objects, scattered objects, and a moving turtle. The results report the soft gripper's versatility and demonstrate the vast application potentials of self-adaptive grasping and sensing in various environments, including but are not limited to underwater, which is always a key challenge of grasping technology.

Creating three-dimensional magnetic functional microdevices via molding-integrated direct laser writing

Magnetically driven wireless miniature devices have become promising recently in healthcare, information technology, and many other fields. However, they lack advanced fabrication methods to go down to micrometer length scales with heterogeneous functional materials, complex three-dimensional (3D) geometries, and 3D programmable magnetization profiles. To fill this gap, we propose a molding-integrated direct laser writing-based microfabrication approach in this study and showcase its advanced enabling capabilities with various proof-of-concept functional microdevice prototypes. Unique motions and functionalities, such as metachronal coordinated motion, fluid mixing, function reprogramming, geometrical reconfiguring, multiple degrees-of-freedom rotation, and wireless stiffness tuning are exemplary demonstrations of the versatility of this fabrication method. Such facile fabrication strategy can be applied toward building next-generation smart microsystems in healthcare, robotics, metamaterials, microfluidics, and programmable matter.