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This article presents a study on a new high torque asymmetric dual chamber soft actuator (ADCSA), aimed to discover the bending performance of ADCSA as an actuator on the human knee for assistance. First, a novel ADCSA design concept for lower limb is proposed, which can be used as an actuating module in an assistance exoskeleton. An ADCSA is composed of two single soft actuators (SSAs) in different sizes. Secondly, multiscale models are established to describe mechanical characteristics of SSAs and ADCSAs. The models are used to optimize the optimal solution for ADCSA. Thirdly, the length of the small SSA in the ADCSA is optimized to get a better actuating effect (i.e., bending torque, hindering torque, bending angle and stiffness) and wear comfort. In the end, we selected a length of 78 mm for the small SSA in ADCSA. The bending torque can reach 33.89 N m (400 kPa), the hindering torque can reach 11.75 N m (400 kPa), the bending angle can reach 1.57 rad and the stiffness can reach 21.72 N m/rad. The proposed ADCSA has potential applications in bionic and assistance robots. [Display omitted] • A novel high torque asymmetric dual chamber soft actuator design concept for lower limb is proposed. • Multiscale models are established to describe mechanical characteristics of SSAs and ADCSAs. The models are used to optimize the optimal solution for ADCSA. • The bending torque can reach 33.89 Nm (400 kPa), the hindering torque can reach 11.75 Nm (400 kPa), the bending angle can reach 1.57 rad and the stiffness can reach 21.72 Nm/rad. [ABSTRACT FROM AUTHOR]

Matching the rich multimodality of natural organisms, i.e., the ability to transition between crawling and swimming, walking and jumping, etc., represents a grand challenge in the fields of soft and bio‐inspired robotics. Here, a multimodal soft robot locomotion using highly compact and dynamic bistable soft actuators is achieved. These actuators are composed of a prestretched membrane sandwiched between two 3D printed frames with embedded shape memory alloy (SMA) coils. The actuator can swiftly transform between two oppositely curved states and generate a force of 0.3 N through a snap‐through instability that is triggered after 0.2 s of electrical activation with an input power of 21.1 ± 0.32 W (i.e., electrical energy input of 4.22 ± 0.06 J. The consistency and robustness of the snap‐through actuator response is experimentally validated through cyclical testing (580 cycles). The compact and fast‐responding properties of the soft bistable actuator allow it to be used as an artificial muscle for shape‐reconfigurable soft robots capable of multiple modes of SMA‐powered locomotion. This is demonstrated by creating three soft robots, including a reconfigurable amphibious robot that can walk on land and swim in water, a jumping robot (multimodal crawler) that can crawl and jump, and a caterpillar‐inspired rolling robot that can crawl and roll. [ABSTRACT FROM AUTHOR]

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Despite smart actuators and sensors have attracted tremendous attention and experienced a very rapid growth in the past few years, the integration of sensing elements in actuators and the simultaneous realization of actuating and sensing tasks remain great challenges. To address this issue, we developed a multi-responsive actuation composite film with integrated resistance sensing capabilities. The actuator which was fabricated by combing MXene–graphene oxide (MGO) and commercial biaxially oriented polypropylene tape (BOPP) showed a large bending range, a fast-bending rate, and highly repeatability under humidity, near-infrared light, and applied voltage stimuli. More importantly, the MGO/BOPP film also exhibited a strain-sensitive resistance, and could be used to monitor human motion parameters and its actuation response. The actuation process of an artificial gripper with self-sensing capabilities based on the MGO/BOPP film could be monitored and recorded in real time to achieve simultaneous actuation and sensing; therefore, the present system holds great promise for soft smart robotics, flexible wearable devices, and other integrated multifunctional systems. [Display omitted] • A multiresponsive soft actuator with integrated self-sensing capabilities is proposed. • Sensor is capable of detecting various physiological human motion with high repeatability and sensitivity. • The resulting actuators showed excellent actuating performances under humidity, NIR irradiation, or voltage stimuli. • The actuator can be used as bionic robotics with real-time motion perception. [ABSTRACT FROM AUTHOR]

In nature, some animals, such as snakes and octopuses, use their limited body structure to conduct various complicated tasks not only for locomotion but also for hunting. Their body segments seem to possess the intelligence to adapt to environments and tasks. Inspired by nature, a modular soft robot with integrated locomotion and manipulation abilities is presented in this paper. A soft modular robot is assembled using several homogeneous cubic pneumatic soft actuator units made of silicone rubber. Both a mathematical model and backpropagation neural network are established to describe the nonlinear deformation of the soft actuator unit. The locomotion process of the chain-type soft robot is analyzed to provide a general rhythmic control principle for modular soft robots. A vision sensor is adopted to control the locomotion and manipulation processes of the modular soft robot in a closed loop. The experimental results indicate that the modular soft robot put forward in this paper has both locomotion and manipulation abilities. [ABSTRACT FROM AUTHOR]

This paper presents an innovative nonlinear model of a self-sensing soft actuator and a switching extended Kalman filter, which is used as an observer for health monitoring such as a virtual sensor. Hardware-in-the-loop simulations and measurements justify the observation strategy. An adaptive position control structure based on the discrete wavelet packets transform method is proposed. Stimulus-responsive polymers are relevant for the realization of smart systems (capable of both sensing and actuating) in the context of soft actuators, for example, in bioinspired robotics, orthotic, and prosthetic technology. A real-time implementation of health monitoring techniques is important to guarantee a gentle, fault-free operation of the soft actuator in the presence of loads. The presented case shows a microrobotic application and measured results show the effectiveness of the developed observer regarding the soft actuator temperature to guarantee its longevity. The latter is necessary for normal operation without a test bench, because the states cannot be measured, but they need to be known for the implementation of the proposed health monitoring algorithms. [ABSTRACT FROM AUTHOR]

Currently, soft robots alone cannot obtain the same operating speed as rigid robots, while rigid robots are not safe enough for human-robot interaction. To address this problem, this paper describes a hybrid robot system that combines both rigid and flexible systems for unknown domain exploration. The system consists of a four-wheeled robot chassis and a cylindrical pneumatic soft actuator, and finally, a computer is used to coordinate and control both. The hardware of the robot system is designed, a bending motion model is proposed, and SOFA framework is used to carry out finite element simulation (FEM) to verify the reasonableness of the design; linear motion speeds of up to 0.5 m/s, higher than the existing soft robots investigated, were verified experimentally separately after carrying the new module, and steering ability was retained; and the robot carrying the navigation module is verified to have a certain map building and localization function through the construction of the simultaneous localization and mapping (SLAM) experimental platform. The hybrid robot introduced in this paper can move quickly on flat terrain and can use its soft part to avoid wear and tear. [ABSTRACT FROM AUTHOR]

Soft robots are intrinsically capable of adapting to different environments by changing their shape in response to interaction forces. However, sensory feedback is still required for higher level decisions. Most sensing technologies integrate separate sensing elements in soft actuators, which presents a considerable challenge for both the fabrication and robustness of soft robots. Here we present a versatile sensing strategy that can be retrofitted to existing soft fluidic devices without the need for design changes. We achieve this by measuring the fluidic input that is required to activate a soft actuator during interaction with the environment, and relating this input to its deformed state. We demonstrate the versatility of our strategy by tactile sensing of the size, shape, surface roughness and stiffness of objects. We furthermore retrofit sensing to a range of existing pneumatic soft actuators and grippers. Finally, we show the robustness of our fluidic sensing strategy in closed-loop control of a soft gripper for sorting, fruit picking and ripeness detection. We conclude that as long as the interaction of the actuator with the environment results in a shape change of the interval volume, soft fluidic actuators require no embedded sensors and design modifications to implement useful sensing. In existing soft robotic sensing strategies, additional components and design changes are often required to sense the environment. Zou et al. introduce a retrofit self-sensing strategy for soft pneumatic actuators, utilizing internal pressure variations arising from interactions. [ABSTRACT FROM AUTHOR]

Provision of modified foods and drinks is one of the approaches for dysphagia management, which is based on the assumption that food with proper texture and rheological properties will allow dysphagia patients to swallow safely and maintain adequate nutrition. However, lack of information about the in vivo swallowing process and its interaction with food flow has obstructed the effective management of dysphagia. In the esophageal swallowing stage, masticated food is transported through the esophagus to the stomach by a peristaltic mechanism, which is generated by sequential contraction and relaxation of esophageal muscles. Inspired by this behavior, a soft actuator is proposed to provide a nonrisk environment aiming to facilitate investigations of the most effective properties of food for the management of the swallowing disorders. The wave-like motion is first specified according to the in vivo measurement of human esophageal peristalsis. Finite-element analysis simulations are carried out to aid the structure design before prototype manufacture. Constructed by casting silicon rubber in a three-dimensional (3-D) printed customized mold, the novel actuator has soft structure resembling its human counterpart, which has a flexible muscular structure. Multiple layers of inflatable chambers are embedded and distributed along the axis of a food passage regularly, which locates at the center of the actuator. The actuator is capable of generating a peristaltic wave and pushing a bolus along the passage. The closure of the tube and the velocity of the propagation wave are going to be adjusted to achieve the trajectories recorded experimentally, by regulating the compressed air pressure pumped into chambers actively. [ABSTRACT FROM PUBLISHER]

A modular soft actuator with snakeskin-inspired scales that generates an anisotropic friction force is designed and evaluated in this study. The actuator makes it possible to fabricate soft robots that can move on various surfaces in the natural environment. For existing modulus soft robots, additional connectors and several independent pneumatic pumps are required. However, we designed precise connection and snake-scale structures integrated with a single pneumatic modular actuator unit. The precise structure was printed using a DLP 3D printer. The movement characteristics of the soft robot changed according to the angle of the scale structure, and the movement distance increased as the number of modular soft actuator units increased. Soft robots that can move in operating environments such as flat land, tubes, inclined paths, and water have been realized. Furthermore, soft robots with modularization strategies can easily add modular units. We demonstrate the ability to deliver objects 2.5 times heavier than the full weight of the soft robot by adding tong-like structure to the soft robot. The development of a soft robot inspired by snakeskin suggests an easy approach to soft robots that enables various tasks even in environments where existing robots have limited activity. [ABSTRACT FROM AUTHOR]

In article number 1806698, Guoying Gu, Qi Ge, and co‐workers develop a paradigm to design and manufacture fast‐response, stiffness‐tunable (FRST) soft actuators via hybrid multimaterial 3D printing. The robotic gripper with three FRST actuators demonstrates a high load capacity and shape adaptivity by lifting objects with arbitrary shapes and various weights spanning from less than 10 g to 1.5 kg. [ABSTRACT FROM AUTHOR]

This article presents a novel tetrahedral soft-legged robot for multigait locomotion, including steering, crawling, and rolling along three different directions. The proposed robot has a compact structure with four active soft legs plugged together onto a rigid pivot. Each active soft leg is made of a novel pneumatic omnidirectional bending soft actuator. Locomotion is achieved by the sequential bending actuation of soft legs. Different inflation sequences are used to drive the soft legs to bend and realize multigait locomotion. Multiple gaits are analyzed with dynamic simulation methods. By discretizing the continuous soft leg into rigid links hinged end-to-end, a multibody dynamics model is built to simulate the robot dynamics and verify the feasibility of multigait locomotion. The crawling speed can reach 3.7 mm· $\text{s}^{-1}$ , the steering speed can reach 1.1 $^\circ \text{s}^{-1}$ , and the rolling speed can reach 5.5 $^\circ \text{s}^{-1}$ and 20.6 mm· $\text{s}^{-1}$. Experimental and simulation results show the capability of multigait locomotion of the proposed robot. The proposed robot has potential applications in search and rescue. [ABSTRACT FROM AUTHOR]

In order to understand fluid transport throughout esophageal swallowing in man, a biologically inspired soft-robotic peristaltic actuator has been designed and manufactured to perform biomimetic swallowing. To achieve congruence with current mathematical modeling techniques for esophageal peristalsis, this paper examines the capability of the device (empirical) towards achieving sinusoidal transport waves with variations of clinically significant parameters such as amplitude and wavelength. The performance of the device to fit the commanded trajectory, by minimization of mean squared error, is tested over the range of wavefront length 30 $\le \lambda /2 \le$ 60 mm and amplitude 6–8 mm in a two-dimensional capability analysis. It is found that the device is capable of achieving propagation of families of wave shapes with less than 5% full scale mean error, which improves for increasing wavefront length and reducing amplitude. The aim for the device in the future is to inspire a novel rheometric technique in the physical domain which characterizes fluid formulations based on intrabolus pressure signatures. This analysis expresses the trajectory generation technique and performance of the novel device to produce continuous peristaltic waves towards biomimetic swallowing. [ABSTRACT FROM PUBLISHER]

Plants can autonomously adjust their growth direction based on the gravitropic response to maximize energy acquisition, despite lacking nerves and muscles. Endowing soft robots with gravitropism may facilitate the development of self‐regulating systems free of electronics, but remains elusive. Herein, acceleration‐regulated soft actuators are described that can respond to the gravitational field by leveraging the unique fluidity of liquid metal in its self‐limiting oxide skin. The soft actuator is obtained by magnetic printing of the fluidic liquid metal heater circuit on a thermoresponsive liquid crystal elastomer. The Joule heat of the liquid metal circuit with gravity‐regulated resistance can be programmed by changing the actuator's pose to induce the flow of liquid metal. The actuator can autonomously adjust its bending degree by the dynamic interaction between its thermomechanical response and gravity. A gravity‐interactive soft gripper is also created with controllable grasping and releasing by rotating the actuator. Moreover, it is demonstrated that self‐regulated oscillation motion can be achieved by interfacing the actuator with a monostable tape spring, allowing the electronics‐free control of a bionic walker. This work paves the avenue for the development of liquid metal‐based reconfigurable electronics and electronics‐free soft robots that can perceive gravity or acceleration. [ABSTRACT FROM AUTHOR]

Soft robots are interesting examples of hyper-redundancy in robotics. However, the nonlinear continuous dynamics of these robots and the use of hyper-elastic and visco-elastic materials make modeling these robots more complicated. This study presents a geometric inverse kinematics (IK) model for trajectory tracking of multi-segment extensible soft robots, where each segment of the soft actuator is geometrically approximated with a rigid links model to reduce the complexity. In this model, the links are connected with rotary and prismatic joints, which enable both the extension and rotation of the robot. Using optimization methods, the desired configuration variables of the soft actuator for the desired end-effector positions were obtained. Furthermore, the redundancy of the robot is applied for second task applications, such as tip angle control. The model's performance was investigated through kinematics and dynamics simulations and numerical benchmarks on multi-segment soft robots. The results showed lower computational costs and higher accuracy compared to most existing models. The method is easy to apply to multi-segment soft robots in both 2D and 3D, and it was experimentally validated on 3D-printed soft robotic manipulators. The results demonstrated the high accuracy in path following using this technique. [ABSTRACT FROM AUTHOR]

A new biomimetic linear actuator named Antagonistically Driven Linear Actuator (ANTLA) that could be directly employed in both macro and microscale of robotic applications is introduced in the present work. The presented actuator provides cost effectiveness and simple fabrication process thanks to its plain construction. In addition to producing basic bidirectional rectilinear motions, the actuator is able to modulate its compliance that might be one of the critical elements of the actuator functionality for the biomimetic applications. For the test, the proposed actuator concept is fabricated and assembled in a microscale robot that generates annelid motion. [ABSTRACT FROM PUBLISHER]

Soft robotics are attractive to researchers and developers due to their potential for biomimicry applications across a myriad of fields, including biomedicine (e.g., surgery), the film industry (e.g., animatronics), ecology (e.g., physical 'animats'), human–robot interactions (e.g., social robots), and others. In contrast to their rigid counterparts, soft robotics offer obvious actuation benefits, including their many degrees of freedom in motion and their potential to mimic living organisms. Many material systems have been proposed and used for soft robotic applications, involving soft actuators, sensors, and generators. This review focuses on dielectric elastomer (DE)-based actuators, which are more general electro-active polymer (EAP) smart materials. EAP-based soft robots are very attractive for various reasons: (a) energy can be efficiently (and readily) stored in electrical form; (b) both power and information can be transferred rapidly via electrical phenomena; (c) computations using electronic means are readily available. Due to their potential and benefits, DE-based actuators are attractive to researchers and developers from multiple fields. This review aims to (1) provide non-experts with an "easy-to-follow" survey of the most important aspects and challenges to consider when implementing DE-based soft actuators, and (2) emphasize current solutions and challenges related to the materials, controls, and portability of DE-based soft-actuator systems. First, we start with some fundamental functions, applications, and configurations; then, we review the material models and their selection. After, we outline material limitations and challenges along with some thermo-mechano-chemical treatments to overcome some of those limitations. Finally, we outline some of the control schemes, including modern techniques, and suggest using rewritable hardware for faster and more adaptive controls. [ABSTRACT FROM AUTHOR]

This paper presents the design, development, and testing of a robot that combines soft-body grasping and crawling locomotion to navigate tubular objects. Inspired by the natural snakes' climbing locomotion of tubular objects, the soft robot includes proximal and distal modules with radial expansion/contraction for grasping around the objects and a longitudinal contractile–expandable driving module in-between for providing a bi-directional crawling movement along the length of the object. The robot's grasping modules are made of fabrics, and the crawling module is made of an extensible pneumatic soft actuator (ePSA). Conceptual designs and CAD models of the robot parts, textile-based inflatable structures, and pneumatic driving mechanisms were developed. The mechanical parts were fabricated using advanced and conventional manufacturing techniques. An Arduino-based electro-pneumatic control board was developed for generating cyclic patterns of grasping and locomotion. Different reinforcing patterns and materials characterize the locomotor actuators' dynamical responses to the varying input pressures. The robot was tested in a laboratory setting to navigate a cable, and the collected data were used to modify the designs and control software and hardware. The capability of the soft robot for navigating cables in vertical, horizontal, and curved path scenarios was successfully demonstrated. Compared to the initial design, the forward speed is improved three-fold. [ABSTRACT FROM AUTHOR]

To date, injection molding has not been a practical manufacturing method for soft robots due to machine costs, large volumes of liquid silicones required, and the inability to change materials quickly between shots. Injection molds are typically machined from metals to allow for high pressure and clamping forces, which further limits the ability to rapidly prototype soft robots when molds could cost thousands of dollars. To circumvent these issues, a low‐cost injection molding system and process are pioneered. In this article, the apparatus, design process, economics, and workflow are described using standard stereolithography and polyjet 3D printers to rapidly iterate on soft robot designs. The mold design process is further detailed to allow for proper material flow, clamping, alignment, and rapid curing times. Static mixing nozzle efficacy is characterized with common silicone materials compared to manual mixing and centrifugal planetary mixing. Lastly, a number of applications that could only be achieved through injection molding due to geometry, embedded components, or cure times are presented. [ABSTRACT FROM AUTHOR]

More recently, soft actuators have evoked great interest in the next generation of soft robots. Despite significant progress, the majority of current soft actuators suffer from the lack of real‐time sensory feedback and self‐control functions, prohibiting their effective sensing and multitasking functions. Therefore, in this work, a near‐infrared‐driven bimorph membrane, with self‐sensing and feedback loop control functions, is produced by layer by layer (LBL) assembling MXene/PDDA (PM) onto liquid crystal elastomer (LCE) film. The versatile integration strategy successfully prevents the separation issues that arise from moduli mismatch between the sensing and the actuating layers, ultimately resulting in a stable and tightly bonded interface adhesion. As a result, the resultant membrane exhibited excellent mechanical toughness (tensile strengths equal to 16.3 MPa (||)), strong actuation properties (actuation stress equal to 1.56 MPa), and stable self‐sensing (gauge factor equal to 4.72) capabilities. When applying the near‐infrared (NIR) laser control, the system can perform grasping, traction, and crawling movements. Furthermore, the wing actuation and the closed‐loop controlled motion are demonstrated in combination with the insect microcontroller unit (MCU) models. The remote precision control and the self‐sensing capabilities of the soft actuator pave a way for complex and precise task modulation in the future. [ABSTRACT FROM AUTHOR]

Pneumatic soft actuators possess relatively fast response, inherent high flexibility, and achieve extraordinary shape morphing under large deformations. Conventionally, the entire body of soft pneumatic robots needs to be designed for specific applications. Herein, a soft pneumatic actuator design with structured fabrics as actuator skins, which has high bending stiffness variation that can accomplish multiple tasks and different deformation modes in a single body, is proposed. By adjusting the structured skin, the developed soft actuator can be tailored to achieve various deformations. It is experimentally shown that the bending stiffness of the actuator can be adjusted from 108 to 5654 N m−1. The blocking force of the actuator in bending is comparable with that of conventional fabric‐reinforced pneumatic actuators, while the actuator skins are reusable and programmable. In application, the actuators are used to construct a bionic soft gripper with multiple degrees of freedom. By switching between three grasping modes, the gripper successfully fulfills a series of tasks including lifting weights up to 1 kg and grasping objects ranging from a grain of grape to a large iron basin. This work opens up an avenue for designing structured skins for pneumatic robots with programmable deformation modes and versatile functions. [ABSTRACT FROM AUTHOR]

Pneumatic soft robotic systems show remarkable potentials in producing versatile locomotion and manipulations, owing to their flexibility in structural design and material selections. However, fabrication of pneumatic soft robotic systems with complex 3D structures and material distribution still remains elusive. Herein, a mode‐free fabrication approach, called planar laser cutting and stacking fabrication (PLCSF), is proposed to create pneumatic soft robotic systems with multi‐material and complex structure, which involves the following steps: 1) slicing the 3D model of desired pneumatic soft robotic systems into 2D layers; 2) fabricating each layer via laser cutting corresponding 2D membrane; 3) stacking all layers together to finish the fabrication. With the PLCSF approach, various prevalent pneumatic soft actuators are fabricated with complex structures (including fiber‐reinforced and pneu‐net) and different actuation modes (such as bending, elongation, twisting, abduction, contraction, and grabbing). The scalability of the PLCSF approach to fabricate multiple degrees‐of‐freedom (DOFs) pneumatic soft actuators with integrated structures, such as twisting‐bending pneumatic soft actuators for delivering and bending‐elongation‐bending pneumatic soft actuators for crawling, is also demonstrated. It is further demonstrated that the PLCSF approach also enables creating a bio‐inspired soft hand with nine DOFs, capable of various dexterous motions and manipulations. [ABSTRACT FROM AUTHOR]

Soft actuator is the main technology that drives the development of soft robotics as it defines the capabilities of soft machines. One of the key challenges in soft actuator research is to simultaneously produce complex morphing (e.g., surface morphing) and high force. Therefore, a soft robotic pad (SRP) was developed as a new soft actuator that can potentially tackle this challenge. This article demonstrates the highly flexible customization process of the SRP regarding fabrication, morphing design, and force scaling for a challenging application: a giant manta ray robot with the Mobuliform swimming mode. Soft robotic pectoral fins (SRPFs) are customized using the SRP technology for the robot. Detailed characterization results show that the SRPFs can generate almost 100 N force or 25 Nm torque with a dual curving motion to mimic the manta ray fin kinematics. The SRPFs are able to propel the manta ray robot to a decent swimming speed with biomimetic fin motions. As a new member of the soft actuator family, SRPs exhibit strong capabilities through this manta ray robot, and they can potentially become unique tools for many engineers and researchers to tackle challenging applications requiring high force and surface morphing. [ABSTRACT FROM AUTHOR]

Soft robots can create complicated structures and functions for rehabilitation. The posture perception of soft actuators is critical for performing closed-loop control for a precise location. It is essential to have a sensor with both soft and flexible characteristics that does not affect the movement of a soft actuator. This paper presents a novel end-to-end posture perception method that employs flexible sensors with kirigami-inspired structures and long short-term memory (LSTM) neural networks. The sensors were developed with conductive sponge materials. With one-step calibration from the sensor output, the posture of the soft actuator could be calculated by the LSTM network. The method was validated by attaching the developed sensors to a soft fiber-reinforced bending actuator. The results showed the accuracy of posture prediction of sponge sensors with three kirigami-inspired structures ranged from 0.91 to 0.97 in terms of R 2 . The sponge sensors only generated a resistive torque value of 0.96 mNm at the maximum bending position when attached to a soft actuator, which would minimize the effect on actuator movement. The kirigami-inspired flexible sponge sensor could in future enhance soft robotic development. [ABSTRACT FROM AUTHOR]

In recent times, the soft robotics field has been attracting significant research focus owing to its high level of manipulation capabilities unlike traditional rigid robots, which gives room for increasing use in other areas. However, compared to traditional rigid gripper robots, being capable of controlling/obtaining overall body stiffness when required is yet to be further explored since soft gripper robots have inherently less-rigid properties. Unlike previous designs with very complex variable-stiffness systems, this paper demonstrates a soft gripper design with minimum system complexity while being capable of varying the stiffness of a continuum soft robotic actuator and proves to have potential applications in gripping objects of various shapes, weights, and sizes. The soft gripper actuator comprises two separate mechanisms: the pneumatic mechanism for bending control and the mechanical structure for stiffness variation by pulling tendons using stepper motors which compresses the actuator, thereby changing the overall stiffness. The pneumatic mechanism was first fabricated and then embedded into another silicon layer during which it was also merged with the mechanical structure for stiffness control. By first pneumatically actuating the actuator which causes bending and then pulling the tendons, we found out that the actuator stiffness value can be increased up to 145% its initial value, and the gripper can grasp and lift a weight of up to 2.075 kg. [ABSTRACT FROM AUTHOR]

Origami has become an optimal methodological choice for creating complex three-dimensional (3D) structures and soft robots. The simple and low-cost origami-inspired folding assembly provides a new method for developing 3D soft robots, which is ideal for future intelligent robotic systems. Here, we present a series of materials, structural designs, and fabrication methods for developing independent, electrically controlled origami 3D soft robots for walking and soft manipulators. The 3D soft robots are based on soft actuators, which are multilayer structures with a dielectric elastomer (DE) film as the deformation layer and a laser-cut PET film as the supporting flexible frame. The triangular and rectangular design of the soft actuators allows them to be easily assembled into crawling soft robots and pyramidal- and square-shaped 3D structures. The crawling robot exhibits very stable crawling behaviors and can carry loads while walking. Inspired by origami folding, the pyramidal and square-shaped 3D soft robots exhibit programmable out-of-plane deformations and easy switching between two-dimensional (2D) and 3D structures. The electrically controllable origami deformation allows the 3D soft robots to be used as soft manipulators for grasping and precisely locking 3D objects. This work proves that origami-inspired fold-based assembly of DE actuators is a good reference for the development of soft actuators and future intelligent multifunctional soft robots. [ABSTRACT FROM AUTHOR]

• Multi-stimuli-responsive hydrogel is synthesized with liquid metal as an additive. • The influence of NIPAM/AM ratios on mechanical properties of hydrogel is investigated. • The double-layer-structured actuator possesses stimulated deformation performance. • A novel soft robot with double layer structure is designed. • It could realize multi-gait behaviors in multiple environments. PNIPAm thermosensitive hydrogel (TSH) has attracted a lot of attention from academic scholars due to its smart volumetric phase transition response to external weak stimuli. However, it cannot simultaneously balance and optimize its tensile properties and response speed. Then, we developed LM-TSH with liquid metal (LM) as an additive, and its elongation at break can reach 768%. In this work, LM-TSH and magnetic TSH are combined to develop a double-layer TSH actuator with multi-field response behavior, which realizes the dual actuation response to near-infrared (NIR) light and high-frequency alternating magnetic field. In addition, a TSH soft robot with two-layer structure is designed, which can realize multi-gait behaviors such as jumping, transporting cargos, and crossing the height obstacle in multiple environments. [ABSTRACT FROM AUTHOR]

Soft actuators synergic color and shape change behaviors are highly interesting and have a great potential to enable biomimetic robotic devices. However, it remains a grand challenge to achieve color and shape change behaviors on demand for emulating complicated activities of living creatures adjusting to surrounding environments. Herein, photo‐responsive bilayer actuators synergic fluorescence and shape change behaviors are fabricated based on silica carbon dots (Si‐CDs) and liquid crystal elastomers (LCEs). In the design, Si‐CDs/polydimethylsiloxane composite film acting as a photochromic layer provides tunable fluorescence performance under ultraviolet while graphene/LCE composite film functioning as a photo‐actuation layer affords reversible deformation under near‐infrared. Thanks to stable fluorescence and photo‐actuation behaviors of bilayer soft actuators, desired camouflage, and locomotion features are realized in untethered bio‐inspired soft robots such as artificial flytrap and inchworm‐inspired walkers by morphology engineering and driven manner manipulation. This work offers a toolbox for designing multifunctional photo‐responsive soft actuators and promotes them towards untethered bio‐inspired intelligent robotic devices. [ABSTRACT FROM AUTHOR]

The McKibben pneumatic actuator (MPA) is a soft actuator used for performing various practical functions in robots. Particularly, many dynamic robots have been realized using MPAs. However, there is a trade-off between torque generated by MPA and the range of motion of the joint. In this study, we focus on the jumping motion of a leg-type robot and use an elliptical pulley whose moment arm changes depending on the robot's posture. To confirm the effectiveness of the elliptical pulley, the relationship between the knee joint pulley (patella) shape and jumping height was analyzed by simulation, and the shape of the patella maximizing jumping height was determined. It was shown that an elongated elliptical patella shape is more effective for the jumping motion than a circular one. Furthermore, the effectiveness of the analytically determined patella shape was confirmed by experiments using an actual robot. [ABSTRACT FROM AUTHOR]

Advancements in smart manufacturing have embraced the adoption of soft robots for improved productivity, flexibility, and automation as well as safety in smart factories. Hence, soft robotics is seeing a significant surge in popularity by garnering considerable attention from researchers and practitioners. Bionic soft robots, which are composed of compliant materials like silicones, offer compelling solutions to manipulating delicate objects, operating in unstructured environments, and facilitating safe human–robot interactions. However, despite their numerous advantages, there are some fundamental challenges to overcome, which particularly concern motion precision and stiffness compliance in performing physical tasks that involve external forces. In this regard, enhancing the operation performance of soft robots necessitates intricate, complex structural designs, compliant multifunctional materials, and proper manufacturing methods. The objective of this literature review is to chronicle a comprehensive overview of soft robot design, manufacturing, and operation challenges in conjunction with recent advancements and future research directions for addressing these technical challenges. [ABSTRACT FROM AUTHOR]

Robotic locomotion in subterranean environments is still unsolved, and it requires innovative designs and strategies to overcome the challenges of burrowing and moving in unstructured conditions with high pressure and friction at depths of a few centimeters. Inspired by antagonistic muscle contractions and constant volume coelomic chambers observed in earthworms, we designed and developed a modular soft robot based on a peristaltic soft actuator (PSA). The PSA demonstrates two active configurations from a neutral state by switching the input source between positive and negative pressure. PSA generates a longitudinal force for axial penetration and a radial force for anchorage, through bidirectional deformation of the central bellows-like structure, which demonstrates its versatility and ease of control. The performance of PSA depends on the amount and type of fluid confined in an elastomer chamber, generating different forces and displacements. The assembled robot with five PSA modules enabled to perform peristaltic locomotion in different media. The role of friction was also investigated during experimental locomotion tests by attaching passive scales like earthworm setae to the ventral side of the robot. This study proposes a new method for developing a peristaltic earthworm-like soft robot and provides a better understanding of locomotion in different environments. [ABSTRACT FROM AUTHOR]

Bio‐inspired soft robots provide a promising solution for robots working in human‐centered scenarios and interacting with unstructured environments. However, the functional versatility and multimodal sensing of soft robots still need improvements. On one hand, the configuration of a soft robot is predefined during manufacturing; on the other hand, the multimodal perception of the deformable soft actuator is challenging. In this work, a reconfigurable and proprioceptive soft origami module is presented, where two kinds of basic actuation modes (i.e., extension and bending) are realized, and multimodal perception is enabled using a novel foldable self‐inductance sensor. As a result, the origami module can be reconfigured to assemble multifunctional robots that can measure interaction force, body configuration, and other environmental information. Dedicated experiments are performed to validate the performance of the proposed origami module. An intelligent gripper assembled using three origami modules is designed with the capabilities of grasping mode adjustment, grasping force measurement, and the grasping target's size measurement. An intelligent jellyfish is assembled using five origami modules, and equipped with buoyancy adjustment and underwater grasping capabilities. The proposed proprioceptive modular soft origami provides an effective solution for versatile and intelligent soft robot design. [ABSTRACT FROM AUTHOR]

Safe and convenient human‐interactive robots are of great interests to support human life. A pneumatic balloon‐type soft robot operated by air or water pressure has potential for soft and gentle interactions with humans. However, the device design often limits the actuation direction. If this motion can be readily tuned, one design can be used in different applications. This study proposes a transformable pneumatic balloon‐type soft robot using attachable shells. The actuating direction can be tuned by the shell structure over a pneumatic balloon‐based tube. The shells can be fabricated via a 3D printer using hard‐ or soft‐materials. After characterizing the bending force and angle of the soft actuator, three robot applications are demonstrated—walking, grabbing a ball, and an octopus‐like motion. Although the mechanical robustness, especially for soft shells, needs to be improved for practical applications, this concept has potential to realize innovative pneumatic balloon‐based robotics. [ABSTRACT FROM AUTHOR]

Nonskeletal animals such as worms achieve locomotion via crawling. We consider them as an inspiration to design robots that help underline the mechanisms of crawling. In this paper, we aim to identify an approach with the simplest structure and actuators. Our robots consist of cut-and-fold bodies equipped with pneumatically-driven soft actuators. We have developed fabrication techniques for coin-sized robots. Experiments showed that our robots can move up to 4.5 mm/s with straight motion (i.e., 0.1 body lengths per second) and perform cornering and U-turns. We have also studied the friction characteristics of our robots with the ground to develop a multistate model with stick–slip contact conversions. Our theoretical analyses depict comparable results to experiments demonstrating that simple and straightforward techniques can illustrate the crawling mechanism. Considering the minimal robots' structure, this result is a critical step towards developing miniature crawling robots successfully. [ABSTRACT FROM AUTHOR]

Soft robots are compliant, impact resistant, and relatively safe in comparison to hard robots. However, the development of untethered soft robots is still a major challenge because soft legs cannot effectively support the power and control systems. Most untethered soft robots apply a crawling or walking gait, which limits their locomotion speed and mobility. This paper presents an untethered soft robot that can move with a bioinspired dynamic trotting gait. The robot is driven by inflatable soft legs designed on the basis of the pre-charged pneumatic (PCP) actuation principle. Experimental results demonstrate that the developed robot can trot stably with the fastest speed of 23 cm/s (0.97 body length per second) and can trot over different terrains (slope, step, rough terrain, and natural terrains). The robotic dog can hold up to a 5.5 kg load in the static state and can carry up to 1.5 kg in the trotting state. Without any rigid components inside the legs, the developed robotic dog exhibits resistance to large impacts, i.e., after withstanding a 73 kg adult (46 times its body mass), the robotic dog can stand up and continue its trotting gait. This innovative robotic system has great potential in equipment inspection, field exploration, and disaster rescue. [ABSTRACT FROM AUTHOR]

Modular soft robots have strong adaptability and versatility in various application contexts. However, the introduction of connection mechanisms will always either reduce the structural compliance or need extra actuation appendages, resulting in the complexity of the structure and system of the robot. To address these issues, herein, a compliant and passive connection strategy is demonstrated, which is accomplished utilizing the reclosable fasteners (RFs), and other varieties including hook‐and‐loop fasteners, as the connection mechanisms to the soft modules for the rapid assembly of various soft machines. The module is a pneumatic soft actuator with both ends designed with a multifaceted structure to attach the RFs in different orientations, resulting in various assembling patterns, including linear connection, orthogonal connection, and oblique connection. Moreover, an alignment mechanism is also designed to improve the alignment precision between two assembled modules. The versatility of the RF enables soft modules capable of assembling not only between identical modules but also with diverse additional accessories for various application scenarios. Different functional assemblies are demonstrated including soft grippers, soft walking robots, and shape‐morphing electrical devices. This approach to the connection mechanisms provides routes to new modular soft robots and devices. [ABSTRACT FROM AUTHOR]

Fluidic actuation in soft robots traditionally requires a complex assemblage of pumps, regulators, valves, and sensors, often resulting in large and bulky support systems. This added bulk can often hinder a robot's ability to be untethered, perform complex tasks, or bring challenges when it comes to maintenance or upgradeability. To address these limitations, herein, a simple and highly modular bidirectional soft robotic appendage is presented that integrates the pump, flow lines, and actuator into a compact, closed hydraulic system, which is driven by an integrated stepper motor, allowing for positional control and fast response times. The actuator can also be swapped in under five seconds, allowing for rapid reconfiguration. Each component has been thoroughly characterized to determine an overall electrical to mechanical efficiency of the system, and from these calculations, it is demonstrated that the actuator utilizes only 1/15th the required energy to achieve a specific bending angle, and is four‐fold more power‐efficient than similar‐sized soft actuators and pumping systems reported in the literature. The integrated actuator and fluidic engine construct presented here thus represents a major departure from previous soft actuator control platforms in that everything is simplified down to a single self‐contained unit, demonstrating unparalleled versatility and modularity. [ABSTRACT FROM AUTHOR]

Flying insects are remarkably agile and robust. As they fly through cluttered natural environments, they can demonstrate aggressive acrobatic maneuvers such as backflip, rapid escape, and in-flight collision recovery. Current state-of-the-art subgram microaerial-vehicles (MAVs) are predominately powered by rigid actuators such as piezoelectric ceramics, but they have low fracture strength (120 MPa) and failure strain (0.3%). Although these existing systems can achieve a high lift-to-weight ratio, they have not demonstrated insect-like maneuvers such as somersault or rapid collision recovery. In this article, we present a 665 mg aerial robot that is powered by novel dielectric elastomer actuators (DEA). The new DEA achieves high power density (1.2 kW/kg) and relatively high transduction efficiency (37%). We further incorporate this soft actuator into an aerial robot to demonstrate novel flight capabilities. This insect-scale aerial robot has a large lift-to-weight ratio (>2.2:1) and it achieves an ascending speed of 70 cm/s. In addition to demonstrating controlled hovering flight, it can recover from an in-flight collision and perform a somersault within 0.16 s. This work demonstrates that soft aerial robots can achieve insect-like flight capabilities absent in rigid-powered MAVs, thus showing the potential of a new class of hybrid soft-rigid 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 FROM AUTHOR]

Abstract: To add more functionalities and overcome the limitation in conventional soft robots, highly anisotropic soft actuators with color shifting function during actuation is demonstrated for the first time. The electrothermally operating soft actuators with installed transparent metal nanowire percolation network heater allow easy programming of their actuation direction and instantaneous visualization of temperature changes through color change. Due to the unique direction dependent coefficient of thermal expansion mismatch, the suggested actuator demonstrates a highly anisotropic and reversible behavior with very large bending curvature (2.5 cm−1) at considerably low temperature (≈40 °C) compared to the previously reported electrothermal soft actuators. The mild operating heat condition required for the maximum curvature enables the superior long‐term stability during more than 10 000 operating cycles. Also, the optical transparency of the polymer bilayer and metal nanowire percolation network heater allow the incorporation of the thermochromic pigments to fabricate color‐shifting actuators. As a proof‐of‐concept, various color‐shifting biomimetic soft robots such as color‐shifting blooming flower, fluttering butterfly, and color‐shifting twining tendril are demonstrated. The developed color‐shifting anisotropic soft actuator is expected to open new application fields and functionalities overcoming the limitation of current soft robots. [ABSTRACT FROM AUTHOR]

In this paper, we propose a forceps grasper using a soft actuator that can estimate grasping force. The grasper consists of a small cylinder and a slider-crank mechanism embedded at the tip of the forceps. A pneumatic soft actuator made of silicone is fabricated and inserted in the cylinder. The grasper is actuated by inflating the soft actuator. It causes no leakage of air, as well it is lightweight and disposable. The developed soft actuator has a built-in strain gauge to measure the displacement of the actuator. By combing the measurements of the strain gauge and the internal pressure, it can estimate the grasping force. We investigated the relationship between the air pressure in the soft actuator and the opening angle of the grasper in order to estimate the force without a force sensor. First, the soft actuator is pressurized from 0kPa to 160kPa at intervals of 10kPa, and the opening angle of the grasper is measured for each pressure without any load on the grasper. The linearity of the soft actuator between the pressure and the opening angle is confirmed. Then, the experiment with the same protocol is conducted while the grasper grasps a force sensor. The estimated force and the output of the force sensor are compared to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Soft actuators with good flexibility, high stability, and excellent controllability have attracted extensive attention. However, dual‐modal smart self‐perception actuator with contact and noncontact actuating mode remains a challenge. Notably, soft actuators with in situ self‐sensing monitoring capabilities have gained increasing attention in smart flexible devices. This work reports a smart actuator composed of polydimethylsiloxane (PDMS)/magnetorheological elastomer (MRE)/Ag/ polyimide (PI) (PMAP), which can not only well respond to bending stimuli but also be actuated by electromagnetic dual‐modal actuation. Benefiting from the nanowire–nanoflake coupling structure of conductive Ag layer, the PMAP film exhibits excellent electrical sensing and electro‐heat generation behavior. The ΔR/R0 of PMAP film increases from 5.1% to 24.7% during the bending test. Moreover, the PMAP film realizes contact electrothermal actuation due to the mismatch of thermal expansion coefficient between PDMS matrix and PI tape. Under applying a 16 s of 2 V electrothermal actuation, the bending angle of PMAP film can increase from 31.1° to 219.3°. Moreover, MRE matrix endows the PMAP film with noncontact magnetic deformation characteristic. This multifunctional smart flexible device integrated with in situ sensing perception and contact and noncontact dual‐modal actuation performances possess high potential in electronic devices and robots. [ABSTRACT FROM AUTHOR]

The unique drive principle and strong manipulation ability of spider legs have led to several bionic robot designs. However, some parameters of bionic actuators still need to be improved, such as torque. Inspired by the hydraulic drive principle of spider legs, this paper describes the design of a bionic actuator characterized by the use of air pressure on each surface and its transmittance in the direction of movement, achieving a torque amplification effect. The produced torque is as high as 4.78 N m. In addition, its torque characteristics during folding motions are similar to those during unfolding motions, showing that the bionic actuator has stable bidirectional drive capability. [ABSTRACT FROM AUTHOR]

This study aims to develop three-dimensional soft robots for special situations that cannot be easily resolved by normal hard-metal robots. We use an ion polymer–metal composite actuator, which is a soft actuator, moved using 1–10 V. The objective of our study is twofold: first, to develop a method to create 3D soft robots; and second, to develop a novel material to increase the performance of soft robots. The actuator fabricated using the proposed material exhibits a performance 113% higher than that of conventional actuators. [ABSTRACT FROM AUTHOR]

Soft robots are considered intrinsically safe with regard to human–robot interaction. This has motivated the development and investigation of soft medical robots, such as soft robotic gloves for stroke rehabilitation. However, the output force of conventional purely soft actuators is usually limited. This restricts their application in stroke rehabilitation, which requires a large force and bidirectional movement. In addition, accurate control of soft actuators is difficult owing to the nonlinearity of purely soft actuators. In this study, a soft robotic glove is designed based on a soft-elastic composite actuator (SECA) that integrates an elastic torque compensating layer to increase the output force as well as achieving bidirectional movement. Such a hybrid design also significantly reduces the degree of nonlinearity compared with a purely soft actuator. A model-based online learning and adaptive control algorithm is proposed for the wearable soft robotic glove, taking its interaction environment into account, namely, the human hand/finger. The designed hybrid controller enables the soft robotic glove to adapt to different hand conditions for reference tracking. Experimental results show that satisfactory tracking performance can be achieved on both healthy subjects and stroke subjects (with the tracking root mean square error (RMSE) < 0.05 rad). Meanwhile, the controller can output an actuator–finger model for each individual subject (with the learning error RMSE < 0.06 rad), which provides information on the condition of the finger and, thus, has further potential clinical application. [ABSTRACT FROM AUTHOR]

With the increasing requirements of underwater missions and the rapid development of soft robotics technologies, soft underwater swimming robots have become a hot topic of research due to their low noise, high flexibility, and high environmental adaptability. In the past 10 years, research into soft underwater robots based on artificial muscle actuation has made considerable progress. Herein, a comprehensive survey on recent advances in soft underwater swimming robots based on different actuation methods is reviewed systematically, including pressure actuation, intelligent material actuation, and biomaterial actuation. First, for each type of actuation, the actuating principle, structural design, and swimming performance of soft underwater robots are introduced in detail. Then, according to the different swimming modes of underwater organisms, the aforementioned soft underwater robots are classified and compared. The results show that for different swimming tasks and application scenarios, the robot needs to realize the optimal design by reasonably selecting the actuating method and the swimming mode. This review summarizes the advanced information and critical technology in designing high‐performance soft underwater robots in the aspect of structural design, actuating methods, and swimming modes and offers an insightful outlook for the future development of soft robots. [ABSTRACT FROM AUTHOR]