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This review summarizes the important properties required for applying soft grippers to agricultural harvesting, focusing on their actuation methods and structural types. The purpose of the review is to address the challenges of limited load capacity and stiffness, which significantly hinder the broader application of soft grippers in agriculture. This paper examines the research progress on variable stiffness methods for soft grippers over the past five years. We categorize various variable stiffness techniques and analyze their advantages and disadvantages in enhancing load capacity, stiffness, dexterity, degree of integration, responsiveness, and energy consumption of soft grippers. The applicability and limitations of these techniques in the context of agricultural harvesting are also discussed. This paper concludes that combined material variable stiffness technology with a motor actuation claw structure in soft grippers is better suited for agricultural harvesting operations of woody crops (e.g., apples, citrus) and herbaceous crops (e.g., tomatoes, cucumbers) in unstructured environments. [ABSTRACT FROM AUTHOR]

In this work, the design and the experimental characterization of a soft gripper which takes inspiration from the octopus tentacle is presented. The system is a single silicone–based pneumatic soft actuator which is able to perform bending motion thanks to its particular geometry and, due to the presence of an embedded suction cup, it can provide enhanced adhesion to the object surface of the goods to be grasped. Firstly, the design aspects as well as the fabrication process of the single-tentacle soft gripper are described. Then, its performances in terms of bending behavior, static deflection, shape variation under applied load and detachment force of the suction cup are evaluated. The experiments include grasping tests of spherical payloads with di ff erent weights. This gripper might have impact in the grasping and manipulation of delicate products like mozzarella in the agrifood field. [ABSTRACT FROM AUTHOR]

Rapid deployment of automation in today's world has opened up exciting possibilities in the realm of design and fabrication of soft robotic grippers endowed with sensing capabilities. Herein, a novel design and rapid fabrication by 3D printing of a mechano‐optic force sensor with a large dynamic range, sensitivity, and linear response, enabled by metamaterials‐based structures, is presented. A simple approach for programming the metamaterial's behavior based on mathematical modeling of the sensor under dynamic loading is proposed. Machine learning models are utilized to predict the complete force–deformation profile, encompassing the linear range, the onset of nonlinear behavior, and the slope of profiles in both bending and compression‐dominated regions. The design supports seamless integration of the sensor into soft grippers, enabling 3D printing of the soft gripper with an embedded sensor in a single step, thus overcoming the tedious and complex and multiple fabrication steps commonly applied in conventional processes. The sensor boasts a fine resolution of 0.015 N, a measurement range up to 16 N, linearity (adj. R2–0.991), and delivers consistent performance beyond 100 000 cycles. The sensitivity and range of the embedded mechano‐optic force sensor can be easily programmed by both the metamaterial structure and the material's properties. [ABSTRACT FROM AUTHOR]

In the realm of underwater exploration and operations, soft robots exhibit considerable application potential due to their capacity for agile and complex deformations as well as their inherent compliance. These characteristics grant them excellent environmental adaptability and reduce damage to delicate samples and organisms. Nonetheless, existing underwater soft robots are primarily designed to mimic the movements of marine organisms or for specific functions, and little attention is paid to the camouflage ability. To address these challenges, in this study, a reconfigurable transparent soft robot with variable stiffness for underwater operations is presented. The design and fabrication methodology of the robot module is presented, followed by the kinematic analysis and stiffness characterization. Leveraging the proposed robot module, a soft manipulator and a soft gripper are designed for underwater operations. The soft manipulator excels in underwater pipeline detection and obstacle avoidance, while the soft gripper showcases considerable load‐bearing capacity (about 71 times its weight), making it suitable for tasks such as retrieving aquatic biological samples or garbage fishing. The proposed reconfigurable soft robot demonstrates robust camouflage capabilities, high environmental adaptability, and notable versatility, suggesting potential solutions to existing challenges in the field of underwater exploration. [ABSTRACT FROM AUTHOR]

Soft grippers, a rapidly growing subfield of soft robotics, utilize compliant and flexible materials capable of conforming to various shapes. This feature enables them to exert gentle yet, if required, strong gripping forces. In this study, we elaborate on the material selection and fabrication process of gripping fingers based on the dielectric elastomer actuation technique. We study the effects of mixing the silicone elastomer with a silicone thinner on the performance of the actuators. Inspired by nature, where the motion of end-effectors such as soft limbs or fingers is, in many cases, directed by a stiff skeleton, we utilize backbones for translating the planar actuation into a bending motion. Thus, the finger does not need any rigid frame or pre-stretch, as in many other DEA approaches. The idea and function of the backbone strategy are demonstrated by finite element method simulations with COMSOL Multiphysics® 6.5. The paper describes the full methodology from material choice and characterization, design, and simulation to characterization to enable future developments based on our approach. Finally, we present the performance of these actuators in a gripper demonstrator setup. The developed actuators bend up to 68.3° against gravity, and the gripper fingers hold up to 10.3 g against gravity under an actuation voltage of 8 kV. [ABSTRACT FROM AUTHOR]

In the realm of underwater exploration and operations, soft robots exhibit considerable application potential due to their capacity for agile and complex deformations as well as their inherent compliance. These characteristics grant them excellent environmental adaptability and reduce damage to delicate samples and organisms. Nonetheless, existing underwater soft robots are primarily designed to mimic the movements of marine organisms or for specific functions, and little attention is paid to the camouflage ability. To address these challenges, in this study, a reconfigurable transparent soft robot with variable stiffness for underwater operations is presented. The design and fabrication methodology of the robot module is presented, followed by the kinematic analysis and stiffness characterization. Leveraging the proposed robot module, a soft manipulator and a soft gripper are designed for underwater operations. The soft manipulator excels in underwater pipeline detection and obstacle avoidance, while the soft gripper showcases considerable load‐bearing capacity (about 71 times its weight), making it suitable for tasks such as retrieving aquatic biological samples or garbage fishing. The proposed reconfigurable soft robot demonstrates robust camouflage capabilities, high environmental adaptability, and notable versatility, suggesting potential solutions to existing challenges in the field of underwater exploration.

Rapid deployment of automation in today's world has opened up exciting possibilities in the realm of design and fabrication of soft robotic grippers endowed with sensing capabilities. Herein, a novel design and rapid fabrication by 3D printing of a mechano‐optic force sensor with a large dynamic range, sensitivity, and linear response, enabled by metamaterials‐based structures, is presented. A simple approach for programming the metamaterial's behavior based on mathematical modeling of the sensor under dynamic loading is proposed. Machine learning models are utilized to predict the complete force–deformation profile, encompassing the linear range, the onset of nonlinear behavior, and the slope of profiles in both bending and compression‐dominated regions. The design supports seamless integration of the sensor into soft grippers, enabling 3D printing of the soft gripper with an embedded sensor in a single step, thus overcoming the tedious and complex and multiple fabrication steps commonly applied in conventional processes. The sensor boasts a fine resolution of 0.015 N, a measurement range up to 16 N, linearity (adj. R2–0.991), and delivers consistent performance beyond 100 000 cycles. The sensitivity and range of the embedded mechano‐optic force sensor can be easily programmed by both the metamaterial structure and the material's properties.

This review summarizes the important properties required for applying soft grippers to agricultural harvesting, focusing on their actuation methods and structural types. The purpose of the review is to address the challenges of limited load capacity and stiffness, which significantly hinder the broader application of soft grippers in agriculture. This paper examines the research progress on variable stiffness methods for soft grippers over the past five years. We categorize various variable stiffness techniques and analyze their advantages and disadvantages in enhancing load capacity, stiffness, dexterity, degree of integration, responsiveness, and energy consumption of soft grippers. The applicability and limitations of these techniques in the context of agricultural harvesting are also discussed. This paper concludes that combined material variable stiffness technology with a motor actuation claw structure in soft grippers is better suited for agricultural harvesting operations of woody crops (e.g., apples, citrus) and herbaceous crops (e.g., tomatoes, cucumbers) in unstructured environments.

The manufacturing industry has witnessed advancements in soft robotics, specifically in robotic grippers for handling fragile or irregular objects. However, challenges remain in balancing shape compliance, structural rigidity, weight, and sensor integration. To address these limitations, a 3D‐printed multimaterial gripper design is proposed. This approach utilizes a single, nearly fully automated 3D printing process to create a universal gripper with almost no assembly work. By processing functional polymer, polymer nanocomposite, and metal wire simultaneously, this technique enables multifunctionality. The gripper achieves different gripping configurations by adjusting joint stiffness through Joule heating of conductive polylactic acid material, ensuring shape conformance. Embedded metal wires, created using an in‐house wire embedding technique, form reliable high‐current‐loading interconnections for the conductive joints acting as the heater. Additionally, an integrated soft sensor printed in thermoplastic polyurethane (TPU) and conductive TPU detects compression levels and discerns handled samples. This study showcases the potential of 3D multimaterial printing for on‐demand fabrication of a smart universal gripper with variable stiffness and integrated sensors, benefiting the automation industry. Overall, this work presents an effective strategy for designing and fabricating integrated multifunctional structures using soft, rigid, and conductive materials, such as polymer, polymer nanocomposite, and metal through multimaterial 3D printing. [ABSTRACT FROM AUTHOR]

Tactile sensing technology is crucial for soft grippers. Soft grippers equipped with intelligent tactile sensing systems based on various sensors can interact safely with the unstructured environments and obtain precise properties of objects (e.g., size and shape). It is essential to develop state‐of‐the‐art sensing technologies for soft grippers to handle different grasping tasks. In this review, the development of tactile sensing techniques for robotic hands is first introduced. Then, the principles and structures of different types of sensors normally adopted in soft grippers, including capacitive tactile sensors, piezoresistive tactile sensors, piezoelectric tactile sensors, fiber Bragg grating (FBG) sensors, vision‐based tactile sensors, triboelectric tactile sensors, and other advanced sensors developed recently are briefly presented. Furthermore, sensing modalities and methodologies for soft grippers are also described in aspects of force measurement, perception of object properties, slip detection, and fusion of perception. The application scenarios of soft grippers are also summarized based on these advanced sensing technologies. Finally, the challenges of tactile sensing technologies for soft grippers that need to be tackled are discussed and perspectives in addressing these challenges are pointed out. [ABSTRACT FROM AUTHOR]

The monitoring of the grasping behavior of variable stiffness grippers has emerged as a challenge due to the increasing use of soft grippers in logistics sorting applications. In this research, a flexible multifunctional sensor is developed by combining a liquid metal microchannel structure with a granular single electrode which detects the bending angle and stiffness of the flexible gripper in real‐time. The novel works by integrating triboelectric nanogenerator with particle interference variable stiffness and detects the stiffness of the soft finger. It is found that increasing the loading force on the gripper by a factor of 2.39 does not affect the kinematic characteristics. The size of the grasped object is determined with 96% accuracy by detecting the resistance offered to the stretched liquid metal during the bending of the soft finger. A soft grasping system is built with multifunctional flexible sensors and the real‐time signal feedback during the grasp‐move‐release process of objects of different diameters and weights is demonstrated. Besides providing a theoretical and experimental foundation of variable stiffness and nondestructive grasping of the soft gripper, the anthropomorphism of the soft grasping gripper is implemented by employing a novel sensor. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in the development of universal soft grippers that can handle objects of varying form factors (including flat objects), surface conditions (including moistened or oily objects), and mechanical properties (deformable and fragile). Yet, there is no single gripper that can gently grip objects with such a wide range of properties. Herein, a soft gripper that combines granular jamming (GJ) and electroadhesion (EA) to gently grasp and release a large set of diverse objects is presented. The gripper can operate in GJ mode only, in EA mode only, or in a combination mode that simultaneously activates GJ and EA. In GJ mode, the gripper can grasp objects with different surface properties, lift objects 38 times its own weight using negative pressure, and release objects by applying positive pressure, but has difficulty in handling flat and fragile objects. In EA mode, the gripper can manipulate flat and fragile objects but encounters difficulties with different surface properties such as oily or moisture. In the combination mode, the gripper can generate grasping forces up to 35% higher than in the GJ mode for all object sizes and certain shapes such as a cylinder. An interactive preprint version of the article can be found here: https://doi.org/10.22541/au.166937296.61200374/v1. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in the development of universal soft grippers that can handle objects of varying form factors (including flat objects), surface conditions (including moistened or oily objects), and mechanical properties (deformable and fragile). Yet, there is no single gripper that can gently grip objects with such a wide range of properties. Herein, a soft gripper that combines granular jamming (GJ) and electroadhesion (EA) to gently grasp and release a large set of diverse objects is presented. The gripper can operate in GJ mode only, in EA mode only, or in a combination mode that simultaneously activates GJ and EA. In GJ mode, the gripper can grasp objects with different surface properties, lift objects 38 times its own weight using negative pressure, and release objects by applying positive pressure, but has difficulty in handling flat and fragile objects. In EA mode, the gripper can manipulate flat and fragile objects but encounters difficulties with different surface properties such as oily or moisture. In the combination mode, the gripper can generate grasping forces up to 35% higher than in the GJ mode for all object sizes and certain shapes such as a cylinder. An interactive preprint version of the article can be found here: https://doi.org/10.22541/au.166937296.61200374/v1.

The rapid development of electronic material and sensing technology has enabled research to be conducted on liquid metal-based soft sensors. The application of soft sensors is widespread and has many applications in soft robotics, smart prosthetics, and human-machine interfaces, where these sensors can be integrated for precise and sensitive monitoring. Soft sensors can be easily integrated for soft robotic applications, where traditional sensors are incompatible with robotic applications as these types of sensors show large deformation and very flexible. These liquid-metal-based sensors have been widely used for biomedical, agricultural and underwater applications. In this research, we have designed and fabricated a novel soft sensor that yields microfluidic channel arrays embedded with liquid metal Galinstan alloy. First of all, the article presents different fabrication steps such as 3D modeling, printing, and liquid metal injection. Different sensing performances such as stretchability, linearity, and durability results are measured and characterized. The fabricated soft sensor demonstrated excellent stability and reliability and exhibited promising sensitivity with respect to different pressures and conditions. [ABSTRACT FROM AUTHOR]

In recent years, many researchers have aimed to construct robotic soft grippers that can handle fragile or unusually shaped objects without causing damage. This study proposes a smart textile-composite actuator and its application to a soft robotic gripper. An active fiber and an inactive fiber are combined together using knitting techniques to manufacture a textile actuator. The active fiber is a shape memory alloy (SMA) that is wire-wrapped with conventional fibers, and the inactive fiber is a knitting yarn. A knitted textile structure is flexible, with an excellent structure retention ability and high compliance, which is suitable for developing soft grippers. A driving source of the actuator is the SMA wire, which deforms under heating due to the shape memory effect. Through experiments, the course-to-wale ratio, the number of bundling SMA wires, and the driving current value needed to achieve the maximum deformation of the actuator were investigated. Three actuators were stitched together to make up each finger of the gripper, and layer placement research was completed to find the fingers' suitable bending angle for object grasping. Finally, the gripping performance was evaluated through a test of grasping various object shapes, which demonstrated that the gripper could successfully lift flat/spherical/uniquely shaped objects. [ABSTRACT FROM AUTHOR]

Magnetic soft grippers have attracted intensive interest due to their untethered controllability, rapid response, and biological safety. However, manipulating living objects requires a simultaneous increase in shape adaptability and gripping force, which are typically mutually exclusive. Increasing the magnetic particle content enhances the magnetic strength but also increases the elastic modulus, leading to low adaptability and high impact force. Here, a porous magnetic soft gripper (PMSG) is developed by integrating a porous structure into a magnetic silicone elastomer. The design of porous hard magnetic composite is characterized by high magnetization, low modulus, and rough surface. It offers the PMSG good compliance, high gripping force, and low impact force at fast gripping. The PMSG is capable of performing a variety of tasks, including the fast and gentle grasping of delicate living objects. The study provides insight into the design of novel magnetic grippers and may offer a promising outlook for biomedical or scientific applications in the manipulation of delicate organisms., (© 2024 Wiley‐VCH GmbH.)

Nowadays, harvesting delicate and high-value fruits, vegetables, and edible fungi requires a large input of manual human labor. The relatively low wages and many health problems the workforce faces make this profession increasingly unpopular. Meanwhile, robotic systems that selectively harvest crops are being developed. Whilst the moving platform, manipulator, and image recognition systems of such robots have been studied the past few decades, research on the gripping end of such robots is only since recently growing. This study analyzes the state-of-the-art of soft grippers for crop handling and harvesting, reporting on their quantitative and qualitative characteristics. Seventy-eight grippers are retrieved from the academic literature and compared with each other in terms of their design and reported performance, more specifically grasping and detachment methods, materials used, type of actuators and sensors employed, and the control of the gripping procedure. In addition, the identified grippers are classified into 13 distinct soft grasping technology categories. Moreover, the retrieved papers are analyzed with respect to their publication date and country of origin to observe trends in the recent growth in the field. Furthermore, a subset of soft grippers is identified that was tested on the task of selectively harvesting crops, where grip and detachment success rates and plant and crop damage are compared.

Soft fluidic actuators produce continuous and life‐like motions that are intrinsically safe, but current designs are not yet mature enough to enable large deployment with high force and low‐cost fabrication methods. Herein, soft fluidic actuators with two superimposed origami architectures are reported. Driven by a fluid input, the presented dual‐origami soft actuators produce quasisequential deployment and bending motion that is guided by unsymmetric unfolding of low‐stretchable origami components. The dominance between the deployment and bending can be shifted by varying the unfolding behavior, enabling preprogramming of the motion. The proposed origami‐inspired soft actuators are directly fabricated by low‐cost fused deposition modeling 3D printing and subjected to heat treatment postprocessing to enhance the fluid sealing performance. Finally, soft gripper applications are presented and they successfully demonstrate gripping tasks where each requires strength, delicacy, precision, and dexterity. The dual‐origami approach offers a design guidance for soft robots to embody grow‐and‐retract motion with a small initial form factor, promising for applications in next‐generation soft robotic systems. An interactive preprint version of the article can be found here: https://www.authorea.com/doi/full/10.22541/au.163698906.68661340. [ABSTRACT FROM AUTHOR]

Soft fluidic actuators produce continuous and life‐like motions that are intrinsically safe, but current designs are not yet mature enough to enable large deployment with high force and low‐cost fabrication methods. Herein, soft fluidic actuators with two superimposed origami architectures are reported. Driven by a fluid input, the presented dual‐origami soft actuators produce quasisequential deployment and bending motion that is guided by unsymmetric unfolding of low‐stretchable origami components. The dominance between the deployment and bending can be shifted by varying the unfolding behavior, enabling preprogramming of the motion. The proposed origami‐inspired soft actuators are directly fabricated by low‐cost fused deposition modeling 3D printing and subjected to heat treatment postprocessing to enhance the fluid sealing performance. Finally, soft gripper applications are presented and they successfully demonstrate gripping tasks where each requires strength, delicacy, precision, and dexterity. The dual‐origami approach offers a design guidance for soft robots to embody grow‐and‐retract motion with a small initial form factor, promising for applications in next‐generation soft robotic systems. An interactive preprint version of the article can be found here: https://www.authorea.com/doi/full/10.22541/au.163698906.68661340.

Soft robotic grippers and hands offer adaptability, lightweight construction, and enhanced safety in human-robot interactions. In this study, we introduce vacuum-actuated soft robotic finger joints to overcome their limitations in stiffness, response, and load-carrying capability. Our design-optimized through parametric design and three-dimensional (3D) printing-achieves high stiffness using vacuum pressure and a buckling mechanism for large bending angles (>90°) and rapid response times (0.24 s). We develop a theoretical model and nonlinear finite-element simulations to validate the experimental results and provide valuable insights into the underlying mechanics and visualization of the deformation and stress field. We showcase versatile applications of the buckling joints: a three-finger gripper with a large lifting ratio (∼96), a five-finger robotic hand capable of replicating human gestures and adeptly grasping objects of various characteristics in static and dynamic scenarios, and a planar-crawling robot carrying loads 30 times its weight at 0.89 body length per second (BL/s). In addition, a jellyfish-inspired robot crawls in circular pipes at 0.47 BL/s. By enhancing soft robotic grippers' functionality and performance, our study expands their applications and paves the way for innovation through 3D-printed multifunctional buckling joints.

The stress‐response strategy is one of the nature's greatest developments, enabling animals and plants to respond quickly to environmental stimuli. One example is the stress‐response strategy of the Venus flytrap, which enables such a delicate plant to perceive and prey on insects at an imperceptible speed by their soft terminal lobes. Here, inspired by this unique stress‐response strategy, a soft gripper that aims at the challenges of high‐speed dynamic grasping tasks is presented. The gripper, called high‐speed soft gripper (HSG), is based on two basic design concepts. One is a snap‐through instability that enables the HSG to sense the mechanical stimuli and actuating instantly. The other one is the spider‐inspired pneumatic‐powered control system that makes the trigger process repeatable and controllable. Utilizing the stress‐response strategy, the HSG can accomplish high‐speed sensing and grasping and handle a dynamic grasping task like catching a thrown baseball. Whereas soft machines typically exhibit slow locomotion speed and low manipulation strength for the intrinsic limitations of soft materials, the exploration of the stress‐response strategy in this study can help pave the way for designing a new generation of practical high‐speed soft robots. [ABSTRACT FROM AUTHOR]

Nature has evolved to shape morphing to adapt to complex environments while engaging with the surroundings. Inspired by this capability, robots are expected to be endowed with the ability to perform shape‐changing, thus interacting with complex environments. Herein, a soft origami actuator with variable effective length (VEL) is proposed to adapt to different objects. The actuator's VEL is realized by an origami structure and actuated by hybrid actuation of tendons and pneumatic pressure. The soft actuator yields motion combining both elongation and bending generated by the asymmetric Yorshimura origami structure. Then an adaptive gripper composed of four origami actuators with programmable effective length is fabricated and its effect on grasping performance is evaluated through both simulations and experiments. Results show that the gripper can grip objects of different shapes, weights, sizes, and textures. This research may shed light on a new soft gripper design using origami structure for the environment's self‐adaptability.

Abstract While suction cups prevail as common gripping tools for a wide range of real‐world parts and surfaces, they often fail to seal the contact interface when engaging with irregular shapes and textured surfaces. In this work, the authors propose a suction‐based soft robotic gripper where suction is created inside a self‐sealing, highly conformable and thin flat elastic membrane contacting a given part surface. Such soft gripper can self‐adapt the size of its effective suction area with respect to the applied load. The elastomeric membrane covering edge of the soft gripper can develop an air‐tight self‐sealing with parts even smaller than the gripper diameter. Such gripper shows 4 times higher adhesion than the one without the membrane on various textured surfaces. The two major advantages, underactuated self‐adaptability and enhanced suction performance, allow the membrane‐based suction mechanism to grip various three‐dimensional (3D) geometries and delicate parts, such as egg, lime, apple, and even hydrogels without noticeable damage, which can have not been gripped with the previous adhesive microstructures‐based and active suction‐based soft grippers. The structural and material simplicity of the proposed soft gripper design can have a broad use in diverse fields, such as digital manufacturing, robotic manipulation, transfer printing, and medical gripping.

A 3D‐printed pneumatically actuated soft suction gripper with an elastomer film is proposed. Suction in such gripper is actively controlled by applying a negative pressure behind the film. The elastomeric gripper body is 3D‐printed, making it easy to customize and integrate into future robotic gripping systems. The gripper can pick a wide variety of objects, such as delicate fruits, small parts, and parts with uneven loads, with high pull‐off forces (over 7.4 N with ∅ 20 mm/55 kPa). The achieved pull‐off forces are significantly higher than the previously reported suction cup grippers with films and more comparable with commercial vacuum grippers. The pull‐off forces show no significant differences with surfaces of varying roughness (up to root‐mean‐square roughness of 5.66 μm) and the gripper is able to pick and release target objects repeatedly. The gripper is also compared with a commercial vacuum gripper with comparable dimensions. It outperforms the commercial gripper in the case of fragile objects, objects smaller than the gripper diameter, and objects with uneven loads. It can apply high pull‐off forces while having controllable release, and is suitable for gripping a wide variety of real‐world objects, including heavy, rough, small, thin, and fragile ones.

Nature has evolved to shape morphing to adapt to complex environments while engaging with the surroundings. Inspired by this capability, robots are expected to be endowed with the ability to perform shape‐changing, thus interacting with complex environments. Herein, a soft origami actuator with variable effective length (VEL) is proposed to adapt to different objects. The actuator's VEL is realized by an origami structure and actuated by hybrid actuation of tendons and pneumatic pressure. The soft actuator yields motion combining both elongation and bending generated by the asymmetric Yorshimura origami structure. Then an adaptive gripper composed of four origami actuators with programmable effective length is fabricated and its effect on grasping performance is evaluated through both simulations and experiments. Results show that the gripper can grip objects of different shapes, weights, sizes, and textures. This research may shed light on a new soft gripper design using origami structure for the environment's self‐adaptability. [ABSTRACT FROM AUTHOR]

While suction cups prevail as common gripping tools for a wide range of real‐world parts and surfaces, they often fail to seal the contact interface when engaging with irregular shapes and textured surfaces. In this work, the authors propose a suction‐based soft robotic gripper where suction is created inside a self‐sealing, highly conformable and thin flat elastic membrane contacting a given part surface. Such soft gripper can self‐adapt the size of its effective suction area with respect to the applied load. The elastomeric membrane covering edge of the soft gripper can develop an air‐tight self‐sealing with parts even smaller than the gripper diameter. Such gripper shows 4 times higher adhesion than the one without the membrane on various textured surfaces. The two major advantages, underactuated self‐adaptability and enhanced suction performance, allow the membrane‐based suction mechanism to grip various three‐dimensional (3D) geometries and delicate parts, such as egg, lime, apple, and even hydrogels without noticeable damage, which can have not been gripped with the previous adhesive microstructures‐based and active suction‐based soft grippers. The structural and material simplicity of the proposed soft gripper design can have a broad use in diverse fields, such as digital manufacturing, robotic manipulation, transfer printing, and medical gripping. [ABSTRACT FROM AUTHOR]

A 3D‐printed pneumatically actuated soft suction gripper with an elastomer film is proposed. Suction in such gripper is actively controlled by applying a negative pressure behind the film. The elastomeric gripper body is 3D‐printed, making it easy to customize and integrate into future robotic gripping systems. The gripper can pick a wide variety of objects, such as delicate fruits, small parts, and parts with uneven loads, with high pull‐off forces (over 7.4 N with ∅ 20 mm/55 kPa). The achieved pull‐off forces are significantly higher than the previously reported suction cup grippers with films and more comparable with commercial vacuum grippers. The pull‐off forces show no significant differences with surfaces of varying roughness (up to root‐mean‐square roughness of 5.66 μm) and the gripper is able to pick and release target objects repeatedly. The gripper is also compared with a commercial vacuum gripper with comparable dimensions. It outperforms the commercial gripper in the case of fragile objects, objects smaller than the gripper diameter, and objects with uneven loads. It can apply high pull‐off forces while having controllable release, and is suitable for gripping a wide variety of real‐world objects, including heavy, rough, small, thin, and fragile ones. [ABSTRACT FROM AUTHOR]

The growing need for manipulators capable of handling delicate objects with care and coexisting safely with humans has brought soft robots to the forefront as a practical and cost-effective solution. In this context, this paper aims to explore soft grippers, a unique and versatile subset of soft robots. It provides an overview of various soft grasping techniques and materials, highlighting their respective advantages and limitations, along with showcasing several designed and tested models. As medicine and agriculture are acknowledged as pivotal domains required for basic human survival, this paper explores the potential applications of soft robotic grippers in these respective fields. Additionally, it further investigates how soft grippers can contribute to reducing cost and enhancing production efficiency while addressing practical relevant solutions. Considering the escalating environmental threats, particularly in oceans and coral reefs, the paper examines the potential of soft grasping underwater to mitigate these challenges, considered as crucial for conserving the fisheries industry and pertinent economic fields. Lastly, it outlines the current challenges and future prospects of soft grippers, emphasizing the importance of overcoming obstacles through finding solutions such as using bioinspiration to create effective technical solutions and highlighting the importance of commercialization. [Display omitted] [ABSTRACT FROM AUTHOR]

Grasping and manipulation are challenging tasks that are nonetheless critical for many robotic systems and applications. A century ago, robots were conceived as humanoid automata. While conceptual at the time, this viewpoint remains influential today. Many robotic grippers have been inspired by the dexterity and functionality of the prehensile human hand. However, multi-fingered grippers that emulate the hand often integrate many kinematic degrees-of-freedom, and thus complex mechanisms, which must be controlled in order to grasp and manipulate objects. Soft fingers can facilitate grasping through intrinsic compliance, enabling them to conform to diverse objects. However, as with conventional fingered grippers, grasping via soft fingers involves challenges in perception, computation, and control, because fingers must be placed so as to achieve force closure, which depends on the shape and pose of the object. Emerging soft robotics research on non-anthropomorphic grippers has yielded new techniques that can circumvent fundamental challenges associated with grasping via fingered grippers. Common to many non-anthropomorphic soft grippers are mechanisms for morphological deformation or adhesion that simplify the grasping of diverse objects in different poses, without detailed knowledge of the object geometry. These advantages may allow robots to be used in challenging applications, such as logistics or rapid manufacturing, with lower cost and complexity. In this perspective, we examine challenges associated with grasping via anthropomorphic grippers. We describe emerging soft, non-anthropomorphic grasping methods, and how they may reduce grasping complexities. We conclude by proposing several research directions that could expand the capabilities of robotic systems utilizing non-anthropomorphic grippers.

Collaborative robots promise to add flexibility to production cells thanks to the fact that they can work not only close to humans but also with humans. The possibility of a direct physical interaction between humans and robots allows to perform operations that were inconceivable with industrial robots. Collaborative soft grippers have been recently introduced to extend this possibility beyond the robot end-effector, making humans able to directly act on robotic hands. In this work, we propose to exploit collaborative grippers in a novel paradigm in which these devices can be easily attached and detached from the robot arm and used also independently from it. This is possible only with self-powered hands, that are still quite uncommon in the market. In the presented paradigm not only hands can be attached/detached to/from the robot end-effector as if they were simple tools, but they can also remain active and fully functional after detachment. This ensures all the advantages brought in by tool changers, that allow for quick and possibly automatic tool exchange at the robot end-effector, but also gives the possibility of using the hand capabilities and degrees of freedom without the need of an arm or of external power supplies. In this paper, the concept of detachable robotic grippers is introduced and demonstrated through two illustrative tasks conducted with a new tool changer designed for collaborative grippers. The novel tool changer embeds electromagnets that are used to add safety during attach/detach operations. The activation of the electromagnets is controlled through a wearable interface capable of providing tactile feedback. The usability of the system is confirmed by the evaluations of 12 users.

Abstract Grasping and manipulation are fundamental ways for many creatures to interact with their environments. Different morphologies and grasping methods of “grippers” are highly evolved to adapt to harsh survival conditions. For example, human hands and bird feet are composed of rigid frames and soft joints. Compared with human hands, some plants like Drosera do not have rigid frames, so they can bend at arbitrary points of the body to capture their prey. Furthermore, many muscular hydrostat animals and plant tendrils can implement more complex twisting motions in 3D space. Recently, inspired by the flexible grasping methods present in nature, increasingly more bio‐inspired soft grippers have been fabricated with compliant and soft materials. Based on this, the present review focuses on the recent research progress of bio‐inspired soft grippers based on impactive gripping. According to their types of movement and a classification model inspired by biological “grippers”, soft grippers are classified into three types, namely, non‐continuum bending‐type grippers, continuum bending‐type grippers, and continuum twisting‐type grippers. An exhaustive and updated analysis of each type of gripper is provided. Moreover, this review offers an overview of the different stiffness‐controllable strategies developed in recent years.

Grasping and manipulation are fundamental ways for many creatures to interact with their environments. Different morphologies and grasping methods of "grippers" are highly evolved to adapt to harsh survival conditions. For example, human hands and bird feet are composed of rigid frames and soft joints. Compared with human hands, some plants like Drosera do not have rigid frames, so they can bend at arbitrary points of the body to capture their prey. Furthermore, many muscular hydrostat animals and plant tendrils can implement more complex twisting motions in 3D space. Recently, inspired by the flexible grasping methods present in nature, increasingly more bio‐inspired soft grippers have been fabricated with compliant and soft materials. Based on this, the present review focuses on the recent research progress of bio‐inspired soft grippers based on impactive gripping. According to their types of movement and a classification model inspired by biological "grippers", soft grippers are classified into three types, namely, non‐continuum bending‐type grippers, continuum bending‐type grippers, and continuum twisting‐type grippers. An exhaustive and updated analysis of each type of gripper is provided. Moreover, this review offers an overview of the different stiffness‐controllable strategies developed in recent years. [ABSTRACT FROM AUTHOR]

Soft robots are considered to have infinite degrees of freedom based on their structural compliance, providing high adaptability to the environments, and recent study has focused mostly on advancement of their physical designs for increasing the adaptability. However, interaction itself with the environment has not been taken into serious account in previous studies despite the importance in applications. A soft robot as a hybrid system described by both discrete and continuous states is considered and a method of analysis for enhanced manipulation is proposed. The method is tested with a soft gripper composed of a pneumatic bending actuator and an embedded soft sensor for a task of object gripping. The optimum sensor location on the actuator based on the calibration map obtained from the actuator characterization is first determined. Using the sensor information, the interaction with the environment (i.e., object) classified into four discrete states is understood. In addition, a control strategy to find the best position to grip the object based on the estimated states is developed. The gripper is able to successfully complete the task using the proposed method for three test scenarios with different initial conditions and control parameters. Finally, the results are demonstrated with supporting videos.

Soft robots are considered to have infinite degrees of freedom based on their structural compliance, providing high adaptability to the environments, and recent study has focused mostly on advancement of their physical designs for increasing the adaptability. However, interaction itself with the environment has not been taken into serious account in previous studies despite the importance in applications. A soft robot as a hybrid system described by both discrete and continuous states is considered and a method of analysis for enhanced manipulation is proposed. The method is tested with a soft gripper composed of a pneumatic bending actuator and an embedded soft sensor for a task of object gripping. The optimum sensor location on the actuator based on the calibration map obtained from the actuator characterization is first determined. Using the sensor information, the interaction with the environment (i.e., object) classified into four discrete states is understood. In addition, a control strategy to find the best position to grip the object based on the estimated states is developed. The gripper is able to successfully complete the task using the proposed method for three test scenarios with different initial conditions and control parameters. Finally, the results are demonstrated with supporting videos. [ABSTRACT FROM AUTHOR]

Fluidic elastomer actuators (FEAs) are popular actuation ways in soft robotics due to their low cost and simple fabrication process. To realize intelligent soft robotic systems, real‐time monitoring of their deformation and interactions with surrounding objects including shape and proximity is important. Thus, integration of sensors into FEAs while considering cost reduction and mass production is required. Because paper features low cost and recyclability, herein, two paper‐based sensors, resistive strain sensors (RSSs) and capacitive proximity sensors (CPSs), are incorporated into FEAs as the strain‐limiting layers. The RSS exhibits the ability to detect the actuated bending angle with hysteresis ≈0.01% and high repeatability for 30 cycles. The RSS is also able to detect different object sizes being grasped by the FEA. In contrast, the CPS starts detecting object proximity 8 mm away from the sensor surface and functions well at various approaching speeds. The CPS is also capable of distinguishing objects of different materials by their permittivity. Finally, an intelligent soft gripper which carries these two sensors is demonstrated, where bending curvature, object proximity, contact, and release are monitored in real time. The results provide a pathway for the development of low‐cost sensorized soft robotic systems with advanced sensing functionalities.

The bending of slide‐ring materials (SRMs), polymer materials having ring‐shaped cross‐linking points providing deterioration tolerance and low hysteresis, is described. An SRM sheet exhibits a voltage‐controllable, extremely large, fast, and bidirectional bending deformation with shape memory functionality. A 50‐μm‐thick SRM sheet actuator exhibits an electrostatic actuation in two opposite directions and bending angle larger than 180° achieved within 0.4 s due to its shape memory effect. The memory effect remains for more than 250 min. As a potential application utilizing the bending of the SRM, a soft gripper is fabricated, which handles two objects placed opposite each other. This functionality is rarely achieved by a soft gripper composed of a single active material, which shows the characteristics of the SRM promising for the development of soft matter systems with novel functionalities and high performances.

This article investigates some aspects related to the design, modeling, prototyping, and testing of soft–rigid tendon-driven grippers. As a case study, we present the design and development of a two-finger soft gripper and exploit it as an example to demonstrate the application scenario of our mathematical model based on screw theory. A mathematical formulation based on screw theory is then presented to model gripper dynamics. The proposed formulation is the extension of a model previously introduced including the mechanical system dynamics. In this type of gripper, it is possible to achieve different behaviors, e.g., different fingertip trajectories, equivalent fingertip stiffness ellipsoids, etc., while keeping the same kinematic structure of the gripper and varying the properties of its passive deformable joints. These properties can be varied in the prototype by properly regulating some manufacturing parameters, such as percentage of printing infill density in a 3D printing process. We performed experiments with the prototype of the gripper and an optical tracking system to validate the proposed mathematical formulation, and to compare its results with other simplified formulations. We furthermore identified the main performance of the gripper in terms of payload and maximum horizontal resisted force, and verified the capabilities of the gripper to grasp objects with different shapes and weights. [ABSTRACT FROM AUTHOR]

Advances in soft robotics and material science have enabled rapid progress in soft grippers. The ability to 3D print materials with softer, more elastic materials properties is a recent development and a key enabling technology for the rapid development of soft robots. However, obtaining the desired mechanical properties (e.g., stiffness) of the soft joints and information about the parameters to select in 3D printers is often not straightforward. In this article, we propose the use of interpenetrating phase composites (IPCs) materials with mathematically generated topologies based on triply periodic minimal surfaces for the development of soft grippers with desired mechanical properties. The flexible joints of the gripper can be realized through two or more phases that are topologically interconnected such that each phase represents a standalone cellular structure. As a case study, we present the design and development of a two-finger soft gripper as an example to demonstrate the application scenario of our approach. The flexible parts with desired stiffness values are realized by using IPCs materials in which the reinforcement distribution can be regulated on the basis of mathematical models. We characterized the properties of the material through a set of quantitative experiments on IPCs material specimens, and then we realized qualitative grasping tests with the gripper and a set of objects with different shapes and sizes. We showed that by properly regulating the properties of IPCs material it is possible to design modular grippers with the same structure, but different closure motions. Grippers can be customized for different tasks by easily assembling and disassembling fingers. [ABSTRACT FROM AUTHOR]

Fluidic elastomer actuators (FEAs) are popular actuation ways in soft robotics due to their low cost and simple fabrication process. To realize intelligent soft robotic systems, real‐time monitoring of their deformation and interactions with surrounding objects including shape and proximity is important. Thus, integration of sensors into FEAs while considering cost reduction and mass production is required. Because paper features low cost and recyclability, herein, two paper‐based sensors, resistive strain sensors (RSSs) and capacitive proximity sensors (CPSs), are incorporated into FEAs as the strain‐limiting layers. The RSS exhibits the ability to detect the actuated bending angle with hysteresis ≈0.01% and high repeatability for 30 cycles. The RSS is also able to detect different object sizes being grasped by the FEA. In contrast, the CPS starts detecting object proximity 8 mm away from the sensor surface and functions well at various approaching speeds. The CPS is also capable of distinguishing objects of different materials by their permittivity. Finally, an intelligent soft gripper which carries these two sensors is demonstrated, where bending curvature, object proximity, contact, and release are monitored in real time. The results provide a pathway for the development of low‐cost sensorized soft robotic systems with advanced sensing functionalities. [ABSTRACT FROM AUTHOR]

Soft end effectors or grippers capable of grasping objects dexterously and efficiently have attracted increasing attention in a broad range of applications. This article describes a smart soft finger‐like actuator with fast response, accurate control, self‐powered pressure, and bending sensing capability by combing the cable‐driven actuation with soft triboelectric nanogenerators (TENGs). The soft actuator, driven by a miniature DC motor, is designed to have multiple segments of elastomer body split with triangular cuts to facilitate the bending actuation and conformal contact with target objects. Two types of TENGs are integrated with the soft actuator: a single‐electrode‐mode TENG to measure the contact pressure and an inner contact–separation‐mode TENG to detect the bending. With micropyramid structures, the tribo‐skin patches possess high sensitivity and good compatibility with the actuator and can actively detect proximity, contact, and pressure via self‐generated electricity. Based on the modular design approach, a gripper with three fingers is fabricated and tested for its grasping, sensing, and self‐powering performance. This gripper is capable of picking up different kinds of objects, providing sensory feedback, and generating electricity, which shows great potential for use in robot–human and robot–environment interaction applications. [ABSTRACT FROM AUTHOR]

The bending of slide‐ring materials (SRMs), polymer materials having ring‐shaped cross‐linking points providing deterioration tolerance and low hysteresis, is described. An SRM sheet exhibits a voltage‐controllable, extremely large, fast, and bidirectional bending deformation with shape memory functionality. A 50‐μm‐thick SRM sheet actuator exhibits an electrostatic actuation in two opposite directions and bending angle larger than 180° achieved within 0.4 s due to its shape memory effect. The memory effect remains for more than 250 min. As a potential application utilizing the bending of the SRM, a soft gripper is fabricated, which handles two objects placed opposite each other. This functionality is rarely achieved by a soft gripper composed of a single active material, which shows the characteristics of the SRM promising for the development of soft matter systems with novel functionalities and high performances. [ABSTRACT FROM AUTHOR]

The end effector is a major part of a robot system and it defines the task the robot can perform. However, typically, a gripper is suited to grasping only a single or relatively small number of different objects. Dexterous grippers offer greater grasping ability but they are often very expensive, difficult to control and are insufficiently robust for industrial operation. This paper explores the principles of soft robotics and the design of low-cost grippers able to grasp a broad range of objects without the need for complex control schemes. Two different soft end effectors have been designed and built and their physical structure, characteristics, and operational performances have been analyzed. The soft grippers deform and conform to the object being grasped, meaning they are simple to control and minimal grasp planning is required. The soft nature of the grippers also makes them better suited to handling fragile and delicate objects than a traditional rigid gripper.

In pome fruit cultivation, apples and pears need to be handled in various processes such as harvesting and sorting. Currently, most processes require a vast amount of manual labor. Combined with a structural shortage of seasonal workers, innovation in this field is crucial. Automated processes could provide a solution wherein the search for an appropriate manipulation tool is essential. Aside from several grippers, customized for harvesting by various researchers, the industry also provides a wide variety of standardized manipulation tools. This paper benchmarks a wide set of the most relevant gripping principles, primarily based on their ability to successfully handle fruit, without causing damage. In addition, energy consumption and general feasibility are evaluated as well. The performed study showed that the customized foam gripper scores the overall best for all test scenarios at the cost of being the least energy efficient. Furthermore, most other gripping tools excelled at certain specific tasks rather than being generally deployable. Impactive grippers are better suited for harvesting at low energy consumption, while astrictive grippers are more suited for sorting tasks constricted by the available space. The results also showed that commercially available soft grippers are not always capable of handling sensitive fruits such as pears without causing damage.