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Haptic display transfers the sense of touch by applying forces, vibrations, or motions to the user. This article presents a novel bidirectional haptic display responsive to touch. The device is composed of a flexible tactile sensor and tactile actuator, and the actuator is actuated according to the touch signals from the tactile sensor. The tactile sensor is a thin array of resistive type sensors that covers the top of the soft dielectric elastomer actuator array. The tactile sensor measures the normal forces (0 $-$ 6 $N$ ) and positions of touches and then sends these signals to control the corresponding tactile actuator cells. The tactile actuator works within the frequency range of 0 $-$ 300 Hz, provides up to 520 $\mu \text{m}$ of displacement and, 600 mN of normal force, much greater than the human hand threshold (50 mN). And thus, the device can transfer different feelings to users. In this research, we develop and evaluate a stand-alone bidirectional haptic display. Then, we took the psychophysical test and introduced the master—slave system whereby the master device controls the slave device depending on the master input.

Traditional actuators, such as motors as well as hydraulic or pneumatic artificial muscles, demonstrate excessive noise, a heavy weight, and a large size, which limit their practical application in many areas. Therefore, for many decades, scientists have worked to develop new types of silent, small, and light actuators. In this article, a novel soft actuator (actuator

Soft robots often show a superior power-to-weight ratio using highly compliant, light-weight material, which leverages various bio-inspired body designs to generate desirable deformations for life-like motions. In this letter, given that most material used for soft robots is light-weight in general, we propose a volumetrically enhanced design strategy for soft robots, providing a novel design guideline to govern the form factor of soft robots. We present the design, modeling, and optimization of a volumetrically enhanced soft actuator (VESA) with linear and rotary motions, respectively, achieving superior force and torque output, linear and rotary displacement, and overall extension ratio per unit volume. We further explored VESA's proprioceptive sensing capability by validating the output force and torque through analytical modeling and experimental verification. Our results show that the volumetric metrics hold the potential to be used as a practical design guideline to optimize soft robots’ engineering performance

A colonoscopy is the most typical method to inspect for colorectal cancer; however, inserting colonoscopes in nonfixed sites, such as the sigmoid colon, requires very skilled insertion techniques. Since the sigmoid colon is one of the most difficult nonfixed sites for insertion, straightening it is a major step in colonoscopy. Previous studies have proposed various methods to assist the colonoscopy insertion process, but there are still challenges that must be addressed in clinical environments. The goal of this study was to assist colonoscopy operators to straighten the sigmoid colon using peristaltic motions generated with a soft actuator mounted on a commercial colonoscope. The peristaltic motions of the proposed system were combined with expanding and extending behaviors, and the straightening strategy was defined based on the analysis of the sigmoid colon handling process of colonoscopy. The peristaltic motions of the soft actuator were implemented using two balloons and a tendon-sheath mechanism. The colon shortening speed was measured to be about 80 mm/min, which contributed to the straightening of the sigmoid colon, thereby helping significantly with the process of colonoscopy.

In this work, we fabricated a fiber-stiffened soft actuator with PEDOT/PSS films as electrode. Embedding nylon fibers in the soft actuator successfully suppressed twisting deformations, resulting in a large and persistent actuation displacement. We evaluated the effects of the fiber spacing (1, 2, 3 and 4 mm) on the displacement and assessed the actuation displacement as a function of applied voltage (0.5, 1.0 and 1.5 V) and frequency (0.2 and 1 Hz) with an actuation time of 500 s. We demonstrated that the fiberstiffened actuator with 2 mm fiber spacing exhibited steady actuation cycles (4.2 mm average displacement) in comparison with those with different spacings (1, 3, and 4 mm) and that without the fiber.

Various complex shapes of dielectric electro-active polymer (DEAP) actuator have been promoted for several types of applications. In this study, the actuation and mechanical dynamics characteristics of a new core free flat DEAP soft actuator were investigated. This actuator was developed by Danfoss PolyPower. DC voltage of up to 2000 V was supplied for identifying the actuation characteristics of the actuator and compare with the existing formula. The operational frequency of the actuator was determined by dynamic testing. Then, the soft actuator has been modelled as a uniform bar rigidly fixed at one end and attached to mass at another end. Results from the theoretical model were compared with the experimental results. It was found that the deformation of the current actuator was quadratic proportional to the voltage supplied. It was found that experimental results and theory were not in good agreement for low and high voltage with average percentage error are 104% and 20.7%, respectively. The resonance frequency of the actuator was near 14 Hz. Mass of load added, inhomogeneity and initial tension significantly affected the resonance frequency of the soft actuator. The experimental results were consistent with the theoretical model at zero load. However, due to inhomogeneity, the frequency response function’s plot underlines a poor prediction where the theoretical calculation was far from experimental results as values of load increasing with the average percentage error 15.7%. Hence, it shows the proposed analytical procedure not suitable to provide accurate natural frequency for the DEAP soft actuator.

The sea cucumber evolved to bear mutable collagenous tissue (MCT) that enables its elastic modulus to change by a factor of 10 within a few seconds. It does this by controlling the amount of chemical regulator released, which can subsequently form or break hydrogen bonds within the MCT. Although existing water-driven, self-operating, soft actuators have great potential for soft robotics, they remain fragile and slow; ergo, their range of application remains modest. Inspired by MCT, we introduce a programmable, powerful, and ultra-fast water-driven self-operating soft actuator exerting an actuation force of approximately 2 N with an actuation speed of approximately 3 s−1 in 80 °C water based on the dramatic stiffness alteration of bulk poly(N-isopropylacrylamide) hydrogel. This actuator also exhibits outstanding robustness by preserving its original shape over multiple cycles of highly strained (300%) actuations under harsh environments. A simple modulation of cross-linker concentration with its dimensional adjustment enabled the precise tuning of not only the actuation force but also the actuation speed in a wide range. Thus, the soft robotic gripper was able to perform a myriad of intricate tasks such as capturing a fragile object, acting as a biomedical appliance, and closing a large wound with uniform appropriate forces.

Shape reconfiguration is ubiquitous in nature and widely used in many applications such as soft robotics, metamaterials, energy absorption and tissue engineering. Shape reconfigurable soft actuators, due to their ability to adapt and adjust in complex and unpredictable working environment, have been designed by the use of various delicate structures and active materials. However, soft actuators that exhibit reconfigurable helical deformation have not been proposed; they have the advantage of integrating both bending and twisting actuations in one deformation mode. In this work, we present a thermal-induced shape reconfigurable soft actuator that shows reversible actuations with vastly shape differences under thermal stimulus. It exhibits helical deformation at lower temperature and mainly in-plane bending at relatively higher temperature. The reversible shape transition is controlled by a thermal stimulus that changes the anisotropy of the structure, which consists of shape memory polymer fibers embedded in a homogeneous elastic matrix. A theoretical model is proposed based on the minimum potential energy that incorporates the thermomechanical behavior of the shape memory polymer fibers. Experiments are conducted and the results agree well with the theoretical modeling. Using the theoretical model, we establish design principles for reconfigurable soft actuators whose functional response is programmable given the architecture and external stimulus. A six-handed helical soft actuator, constructed to demonstrate its programmable deformation, is utilized to catch a living fish in water.

This paper presents a frog-inspired swimming robot based on articulated pneumatic soft actuator. To realize the miniaturization of the robot and enhance its environmental adaptability, combined with the advantages and characteristics of soft materials, an articulated pneumatic soft actuator is designed based on analysis of a frog’s propulsion characteristics. A structural model is established to analyse the mechanical properties of the soft actuator. With the goal of making full use of the driving torque of the actuator and enhancing the propulsion efficiency of the robot, the motion trajectories of each joint of the robot are planned. Based on the trajectory planning, the control strategy of the soft actuator is determined to realize the frog-like swimming of the robot. The torso size after assembly is 0.175 m × 0.100 m × 0.060 m, which realizes the miniaturization of the frog-inspired robot. During the movement of the robot, the torso moves stably and flexibly, and can realize continuous linear and turning movements. The rationality of the structure and trajectory planning are verified by prototype experiments.

This paper introduces the modular design and manufacturing method, mechanical model, and test verification of a new type of soft actuator driven by fluid. First, the modular design scheme and driving principle of omnidirectional bending and elongation of the soft actuator are described. Three print-based elastic air cavities constrained by fire lines are distributed radially inside the actuator. The actuator can complete the 3 DOF motions of omnidirectional bending and elongation. From the basic principle of material mechanics, a novel mechanical model of the soft elastomer actuator is established. By numerically solving the nonlinear model, the relationship between actuator elongation/bending angle and driving pressure is obtained. The theoretical prediction and test results show that the deformation of the actuator exhibits a linear relationship with pressure when the chambers are charged. Additionally, the maximum allowable load force on the actuator terminal also exhibits good linearity when the driving pressure increases. Furthermore, the established mechanical model, which considers gravity effects can more accurately describe the features of bend and elongation of the actuator. The results shows that the proposed model is more convenient than the FEM models. This study provides theoretical support for accurate control of a soft actuator.

Soft actuator materials change their shape or size in response to stimuli like electricity, heat, light, chemical or pH. These actuator materials are compliant and well suited for soft mechatronics and robots. This paper introduces the definition of soft materials and the position of soft actuator materials in comparison with conventional actuators and other solid state actuator materials. A thorough review of selected soft actuator materials is carried out, including responsive gels/hydrogels, ionic polymer metal composites, conducting polymers, carbon nanotubues/graphenes, dielectric elastomers, shape memory polymers and biopolymers. This review will give insights for applications of soft actuator materials via better understanding of the materials in terms of their preparation, performance and limitation.

The flexible soft actuators of conducting polymers can directly convert electrical stimulus into mechanical motions, which can be used for robotics and biomimetic applications. Herein, an electro-responsive membrane actuator based on poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), functionalized single-walled carbon nanotube was fabricated using solution casting method with poly(vinyl alcohol) as a base intermediate polymer membrane. The poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) was evenly ornamented onto the single-walled carbon nanotube/poly(vinyl alcohol) membrane (single-walled carbon nanotube/ poly(vinyl alcohol)/ poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)) surfaces through dip coating and verified by scanning electron and transmission electron microscopy analysis. The desirable bending response of the fabricated single-walled carbon nanotube/ poly(vinyl alcohol)/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) membrane with time at different voltages and generated tip force makes it a promising material as a new-generation conductive polymer-based soft actuator. A permutation of the electrical conductivity, more surface area, and admirable electromechanical properties of the single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) components consequences in the composite electrode exhibited excellent actuation performance compared to the ionic polymer-metal composite actuators with Pt electrodes surface. The fabricated actuator membrane can be employed for artificial muscles, robotics, and other bio-mimetic applications.

Soft actuators and robotics have been widely researched in recent years mainly due to their compliance to environments and safe interaction with humans. However, the need of tether and low energy efficiency of such actuators/robots has limited their practical applications. This article presents a novel tendon-driven soft actuator concept that has the property of self-pumping, called soft self-pumping actuator (SSPA) in this research. A SSPA is designed by assembling two soft pneumatic actuators (SPAs) face-to-face, whose air chambers are connected by two check valves. Actuation of the SSPA is achieved by tendons that allows precise and untethered control compared with traditional SPAs. The two chambers in the proposed actuators are precharged with air to a desired pressure to enlarge self-stiffness and to facilitate bending. When actuated, one chamber will be compressed and serve as a pump to inject its air into the other chamber, resulting in further bending of the actuator. The airflow involves energy transmission to help the intended actuation, thus improving energy efficiency. In experimental studies, differential chamber air pressure is found to reduce the force in initiating actuator bending. Experimental results have also shown that energy efficiency increase of up to 45% has been achieved compared with the same design but without air transmission. We believe that the proposed concept could lead to more novel designs of controllable and energy saving soft robots.

The expensive nature of currently used materials in the soft robotic industry demands the consideration of alternative materials for fabrication. This work investigates the performance of RTV-2 grade silicone rubber for fabrication of a soft actuator. Initially, a cylindrical actuator is fabricated using this material and its performance is experimentally assessed for different pressures. Further, parametric variations of the effect of wall thickness and inflation pressure are studied by numerical methods. Results show that, both wall thickness and inflation pressure are influential parameters which affect the elongation behaviour of the actuator. Thin (1.5 mm) sectioned actuators produced 76.97% more elongation compared to thick sectioned, but the stress induced is 89.61 % higher. Whereas, the thick sectioned actuator (6 mm) showed a higher load transmitting capability. With change in wall thickness from 1.5 mm to 6 mm, the elongation is reduced by 76.97 %, 38.35 %, 21.05 % and 11.43 % at pressure 100 kPa, 75 kPa, 50 kPa and 25 kPa respectively. The induced stress is also found reduced by 89.61 %, 86.66 %, 84.46 % and 68.68 % at these pressures. The average load carrying capacity of the actuator is found to be directly proportional to its wall thickness and inflation pressure.

Soft actuators have demonstrated great potential for utilization in many industrial applications due to their ability to be produced in unusual shapes, their capacity to conform within a containing envelope and their large power to displacement ratios. A great majority of these flexible structures are produced by casting processes, since they are generally composed of silicone materials due to their high elasticity and flexibility. Innovative 3-D printing techniques and flexible materials have been explored and utilized to produce soft actuators to overcome this limitation in production. This paper presents a 3-D printed soft actuator with embedded sensing capabilities and the ability to produce a signal based on its actuation position. Computational simulations were done to evaluate the performance of the actuator with embedded sensing to determine the resistance change in the embedded conductive element based on the deformation of the soft actuator. This work demonstrates control to actuate the soft actuator while sensing its deformation using a resistance-based sensor. The entire structure was produced using fused deposition modeling (FDM) techniques, in one continuous process without support material.

Today, tunable soft elastomeric actuators due to their remotely-controllability, fast-response and stiffening have gained great attention. This article aims to develop analytical and numerical tool...

Exoskeletons are poised to provide motion assistance to aid in rehabilitation and compensate for muscle weaknesses, augment human performance, and reduce repetitive stress injuries in healthcare, industry, and occupation settings, respectively. Soft actuator enabled systems are gaining widespread attention due to their mechanical simplicity, low weight, and compliance to the human body. Regardless of promises shown, the progress for these systems is slow due to a wide variety of actuator types and geometries, which complicate designs and model predictive performance to create application-specific systems. Learning from conventional hard robotic actuator approaches, this paper investigates a modular actuator concept that can be used for creating many exoskeletons and is easily customized for fitting different sized humans, joint types, and application scenarios. The preliminary investigation details the development of an elbow exoskeleton by implementing a modular corrugated diaphragm actuator arranged in a serial configuration. Numerical simulation and experimental evaluations were carried out to investigate the torque, load-bearing, and motion characteristics of the exoskeleton. Results confirmed the viability of the concept by showing that the exoskeleton can provide assistive motion to a forearm and hand of average weight. Additionally, the exoskeleton is able to apply continuous passive motion to an elbow joint, which can be used in rehabilitation settings.

This paper presents a method for determining material constants of hyperelastic material used for building the soft robotic actuators. Sixty testpieces were made of silicone rubber with a shore A hardness from 20 A to 45 A. Each of them was then subjected to the uniaxial tensile test to obtain the stress–strain relationship, which is a key factor to evaluate the compatibility of the common six forms of strain energy density function for hyperelastic material. The sum of square error was used to determine the most relevant constitutive models, which are Ogden third order, Polynomial second order, and Yeoh, as well as parameter values of the corresponding materials. To analyze the appropriateness of these models for computation, six pneumatic soft actuators were built from materials with different hardness and tested for various pressures. From the simulation and experimental results, the model Yeoh has yielded the highest accuracy. This outcome forms a firm basis for the determination of suitable material in the computation and simulation of the pneumatic soft actuator. Besides, the obtained experimental results in this paper could be included in the database of hyperelastic material with different hardness for further simulation in the related field.

In order to improve the bearing capacity of soft actuators, this article presents the development of the rigid-hoop-reinforced (spring or steel hoop) multi-DOF soft actuator. The actuator is composed of a rotary module with spring reinforcement on the silicone rubber-based body and a bending module with steel hoop reinforcement on the body. Compared with fiber-reinforced actuators, the bearing capacities of rigid-hoop-reinforced actuators made of 65Mn spring steel are improved. The radial and the axial bearing capacity for the bending module and the rotary module is raised by 29.6%, 28.2%, 30.6%, 49.6% respectively; under the same pressure, the spring-reinforced interval increases the maximum rotary angle of the rotary module, the steel hoop-reinforced interval increases the maximum bending angle of the bending module; with the same reinforcement type, the bending module with reinforcement interval of 10 mm has good bending characteristics that the bending angle changes with the pressure gently; the lower the hardness of silicone rubber base body, the better the adaptability and flexibility of the actuator, and the higher the hardness, the greater the bearing capacity of the actuator. Due to the above advantages, the rigid-hoop-reinforced multi-DOF soft actuator can be applied to medical devices which need high load-carrying capacity.

Soft robots exhibit many exciting properties due to their softness and body compliance. However, to interact with the environment safely and to perform a task effectively, a soft robot faces a series of challenges such as dexterous motion, proprioceptive sensing, and robust control of its deformable bodies. To address these issues, this article presents a method for fabrication and dynamic modeling of a novel bidirectional bending soft pneumatic actuator that embeds a curvature proprioceptive sensor. The bidirectional bending deformation was generated by two similar chambers with a sinusoidal shape for reducing the internal dampness during bending deformation. An optical waveguide made from flexible poly (methyl methacrylate) material that is immune to the inlet pressure was embedded into the actuator body to measure its bending angle. A dynamic modeling framework based on step response and parameter fitting was proposed to establish a simple differential equation that can describe the nonlinear behavior of the soft actuator. Hence, a sliding mode controller is designed based on this differential equation and the Taylor expansion. The proposed dynamical model and the sliding mode controller were validated by trajectory tracking experiments. The performance of the bidirectional bending soft actuator, such as the linear output of the curvature sensor in different inflating patterns, the proprioceptive sensitiveness to the external environment, the output force, and large bending range under relatively small pressure, was evaluated by relevant experimental paradigms. Prototypes from the novel design and fabrication process demonstrated the soft actuator's potential applications in industrial grasping and hand rehabilitation.

Polymeric materials with compliant inner structures have brought great development to soft actuators, which have characters of low cost, high adaptability and operability, and being competent for complex motions simultaneously. From the viewpoint of muscle physiology, contraction is not limited to the shortening of muscle length but also means that a force can be produced in isometric condition without shortening. Generation of both force and stroke under a given stimulus are two fundamental functions. Accordingly, isometric and isotonic contraction are two main categories. In this work, a semi-crystal-based polyurethane soft actuator (PSA) was fabricated with abilities to perform two basic contractions. Effect of structures and thermodynamic properties on muscle contraction capability were investigated. The degree of contraction can be easily manipulated and memorized by changing crystallinity, chain orientation through preloaded and stimulated conditions. Due to the high sensitivity of crystal phase to temperature, sensing ability are reported here and energy source from enthalpy change are unprecedentedly explored. This work expands mechanism of thermal-stimulated muscle to a new direction and realizes the multi-functions of muscle in one single polymer without any complicated structure design and control system.

A smart soft actuator with multiple capabilities of humidity-driven actuating, humidity energy harvesting, self-powered humidity sensing, and real-time motion tracking is reported. It is designed on the basis of an MXene/cellulose/polystyrene sulfonic acid (PSSA) composite membrane. This actuator is driven by asymmetric expansion under a moisture gradient during capture of the chemical potential of humidity to mechanical power. Meanwhile, the gradient moisture chemistry also induces directional proton diffusion to generate electricity with high power density and open-circuit voltage. A good linear correlation between the humidity sensitivity, electrical signal, and bending state of this actuator allows real-time tracking of motion modes with humidity change without an external power supply. This multifunctional soft actuator can be used for engineering smart switches, artificial fingers, and soft robots with trackable and distinguishable motion patterns, as well as sensitive noncontacting humidity sensor and breathing monitors.

The flexible manipulators and related robotic systems have been widely used in minimally invasive surgery (MIS) for enhancing the intraoperative inspection and surgical operation. Although a variety of flexible manipulators using different mechanisms have been developed, most of them are rigid mechanical structures or single function, which lack softness, robustness or in-situ diagnosis and surgical treatment. To enrich the flexibility and therapeutic function of manipulators, we developed a laser endoscopic manipulator with a soft bendable tip. The soft bendable tip is composed of a spring-reinforced soft actuator with multiple channels, which are designed for placing diagnosis and therapy probes to enrich the integrated diagnosis and therapeutic function. Pilot results show that the actuator can bend and elongate in the three-dimensional space and the spring-reinforced structure increases the linearity and consistency of the soft actuator. Experimental outcomes demonstrate that the proposed robotic system has extended bending capability and integrated diagnosis and therapeutic function. The multiple functions with surgical tools and laser fiber realize in-situ therapy. Therefore, it would be an enhancement for future clinical applications such as single-port laparoscopic surgery (SPL) or neurosurgery.

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection.

Chopsticks are a popular tool used every day by 1.5 billion people to pick up pieces of food of different sizes and shapes. Given that the use of chopsticks requires sophisticated muscle control, they are difficult to use for unskilled people. In this study, a chopstick robot that uses a new soft actuator was developed. Firstly, we developed an X-shaped soft actuator and tested its performance. When a voltage was applied to the actuator, the gap in the X shape was reduced by the resulting electrostatic force. Conversely, when the power was turned off, the actuator recovered its original shape owing to the elasticity of its material. We attached the X-shaped soft actuator between the chopsticks. The chopstick robot, controlled by the input voltage, can pick up various objects in the switched-on state and is able to release them when switched off. We tested the performance of the chopstick robot and analyzed the forces acting on the chopsticks. The robot can be used for picking up various objects. Moreover, the X-shaped actuator can be adapted for use in various studies, through different shapes and configurations.

Carbon polymer composites (CPC) are kind of soft actuators belonging to the category of ionic electroactive polymer transducers. In this work, we present design, modeling, fabrication, and characterization of a novel parallel manipulation system actuated by the CPC actuators. In this system, four actuators are operated in parallel to manipulate an end effector or a platform to generate motion along the different axis. The major advantage of the current system is that the platform and the actuators are fabricated as a single structure using the simple layer-by-layer spray-deposition method with selective masking. The proposed system is highly dexterous and is capable of generating three degrees of motions, namely, roll, pitch, and piston. The initial structural design and its deformation are optimized by modeling and simulating using finite element method and followed by fabrication and characterization to examine its workspace. The experimental results have demonstrated high levels of manipulability from the CPC actuators that are outstanding in the class of soft ionic actuators while keeping the fabrication method simple, scalable and cost-effective. The proposed configuration has potential application in micromanipulation systems that require large deformation in a confined space.

The multi-cavity soft actuator is assembled from single-cavity soft actuator through a reasonable geometric distribution. It has the characteristic that the pneumatic soft actuator is driven by its own deformation and has more degrees of freedom. Pneumatic soft actuator is widely used as an emerging discipline and its strong compliance has been greatly developed and applied. However, as the most application potential type of soft actuators, there is still a lack of simple and effective deformation prediction methods for studying the spatial deformation of multi-cavity soft actuators. To solve this problem, a vector equation method is proposed based on the analysis of the principle of the space deformation of the two-cavity, three-cavity and four-cavity soft actuators. Furthermore, a nonlinear mathematical model of the air pressure, space position and deformation trajectory of the soft actuator end is established by combining the vector equation method. Finally, the three-channel soft actuator is verified through experiments. The results show that the mathematical model can better predict the space deformation trajectory of the soft actuator, which provides a new research method for studying the space deformation of the multi-channel soft actuator.

Soft grippers can be used to grasp objects with various geometric surface structures or stiffness but typically encounter difficulty in providing high grasping force. Although the combination of soft grippers with adhesive technology can increase their load capacity, this approach has disadvantages of compatibility and limited application range. This article has reported a bioinspired design of a soft gripper that integrates flat dry adhesive, soft actuator, and microspine to improve the comprehensive grasping ability of the soft gripper on smooth or rough surfaces. The adhesive strength of flat dry adhesives with different thickness or cross-linking ratios was investigated to ensure that a large grasping force can be provided. Soft actuators with uniform and nonuniform cross-sectional heights were compared, and results indicated that the soft actuator with a nonuniform cross-sectional height exhibited remarkable advantages for designing the integrated gripper. A microspine–spring–shape memory alloy coil structure was designed to control the retraction and protrusion of microspine and distribute the load on rough surfaces evenly. The proposed integrated gripper with the aforementioned design can lift regularly or irregularly shaped objects with smooth or rough surfaces and provide a higher adhesive force than the nonadhesive gripper. After inserting a flexible pressure film sensor into the soft gripper, the surface property of the grasped object can be measured, which is beneficial for the selection of a suitable grasping strategy in unknown environments. The designed gripper can be used in many applications, such as in unmanned aerial vehicles, industrial manipulators, and climbing robots.

In the landscape of Industry 4.0, advanced robotics awaits a growing use of bioinspired adaptive and flexible robots. Collaborative robotics meets this demand. Due to human&ndash, robot coexistence and interaction, the safety, the first requirement to be satisfied, also depends on the end effectors. End effectors made of soft actuators satisfy this requirement. A novel pneumatic bending soft actuator with high compliance, low cost, high versatility and easy production is here proposed. Conceived to be used as a finger of a collaborative robot, it is made of a hyper-elastic inner tube wrapped in a gauze. The bending is controlled by cuts in the gauze: the length and the angular extension of them, the pressure value and the dimensions of the inner tube determine the bending amplitude and avoid axial elongation. A design methodology, oriented to kinematically mirror the shape of the object to be grasped, was defined. Firstly, it consists of the development of a non-linear parametric numerical model of a bioinspired finger, then, the construction of a prototype for the experimental validation of the numerical model was performed. Hence, a campaign of simulations led to the definition of a qualitatively predictive formula, the basis for the design methodology. The effectiveness of the latter was evaluated for a real case: an actuator for the grasping of a light bulb was designed and experimentally tested.

This work describes the control of a pneumatic soft robotic actuator via eye movements. The soft robot is actuated using two supply sources: a vacuum pump and an air supply pump for both negative and positive air supply sources respectively. Two controlled states are presented: the actuation of the vacuum and air pump. Through eye positioning and tracking on the graphical user interface to actuate either pump, a control command is directed to inflate or deflate the pneumatic actuator. The potential of this application is in rehabilitation, whereby eye movements are used to control a rehabilitation-based assistive soft actuator rather than ON/OFF electronics. This is demonstrated in this work using an elbow based rehabilitation soft actuator., Biomedical Engineering; Electrical Engineering; Data Visualization; Computer Engineering; Robotics; Materials Characterization; Structural Analysis; pneumatic actuator; soft robot; pleated network design; corrugated actuator; eye tracker controlled actuator; eye gaze system for control; tobii tracker 4c with soft actuator

International audience; In this paper, we describe the use of calibration techniques to help improving prediction accuracy of models for soft actuators. A finite-difference model considering anisotropy of soft actuator flexible chamber is combined with experimental identification to assess actuator motion. Identifiability conditions are exploited to determine suitable experimental conditions, taking into account the manufacturing process capabilities, multimaterial additive manufacturing in this context. As a second contribution, a soft actuator with Wren mechanism for reinforcement is being developed. It is considered for rotary actuation, with the description of a proof of concept. The interest of the calibration technique and the actuator design are finally discussed.

In this paper, one of the most common and inexpensive additive manufacturing, or 3D printing, technology named fused filament fabrication (FFF) has been used to manufacture a sensing soft actuator which in future could be used for hands and fingers rehabilitation. The innovative element of the proposed soft actuator consists of an embedded strain sensor which, as shown during the characterization phase, provides an electrical resistance change when the actuator is actuated by compressed air. The strain sensor has been embedded into the soft actuator during the manufacturing process: the printing process has been stopped, a 3D printed channel has been filled by means of a silver paste and after its solidification, the manufacturing process has been resumed. In this way a smart soft actuator has been fabricated in a single-step printing cycle by taking advantage from the stop-and-go method.

As soft robots have been popular, interest in soft actuators is also increasing. In particular, new types of actuators have been proposed through bio mimetic. An actuator that we proposed in this study was inspired by a motor cell which enables plants to move. This actuator is an electrostatic actuator utilizing electrostatic attraction and elastic force, and can be used repeatedly. In addition, this actuator, which can produce large and diverse movements by collecting individual movements like a cell, has a wide application field. As one of them, this actuator is stacked to construct a layer structure and propose an application example. In addition, a piezo sensor was built inside the actuator and real - time motion monitoring was attempted. As a result, the point laser sensor value and the piezo sensor value coincided with each other, which means that it is possible to detect motion in real time with the built-in sensor.

Compliant devices are used in a wide variety of applications like soft robots. Although soft robotics have played an important role in providing the desired compliance and reducing the safety concerns on robot–human interactions, the research community soon realized that for a soft robot, not only is the compliance quite important, but also the change in the compliance and its controllability is paramount. In this regard, this research proposes a novel bio-inspired variable stiffness fiber-reinforced dielectric elastomer actuator that performs similar to the tissues of the California two-spot octopus, scientifically known as Octopus bimaculoides. It is shown that by using an initially curved dielectric elastomer strip and by properly incorporating fibers, an interesting variable stiffness actuator can be created that lays the foundation for future bionic fingers and grippers. Using an experimentally validated numerical framework, different geometries of the proposed variable stiffness dielectric elastomer actuator (VSDEA) are simulated by the means of the finite element method. The main outputs of the simulations are the force–displacement curves for different configurations of the proposed VSDEA activated by different voltages ranging from 0 to 7.5 kV. The bending stiffness of the actuators that is the initial slope of the force–displacement curves is calculated and compared for different configurations. By analyzing the outcomes of the simulations, the paper introduces an optimum configuration that is capable of varying the stiffness of the structure up to 99.3% which is a good improvement compared with previous studies.

Textiles are ubiquitous materials and no man-made class of material offers such a proximity to the body and as such ever-presence in human life as textiles. Part of this is due to textiles having the rather unique property of drapability and pliability which is used in clothing. Soft actuators are flexible and typically lightweight and silent and are, therefore, well suited to be integrated in fabrics and textiles, resulting in textile actuators for wearables such as exoskeletons. In this chapter, we address various yarn and fabric actuators and describe two examples of textile actuators, thermal-driven textile actuators, and electrochemical textile actuators, in more detail.

Recently, various types of soft actuators and their applications have been studied in the search for alternatives to conventional robots. In particular, pneumatic soft actuators have the advantages of a light weight and high power. One of the applications of such soft actuators is fusion with flexible structures. However, because these actuatable flexible structures consist of rubber, silicone, or flexible resin, it is difficult for them to support their own weight, owing to the effect of the square-cube law in the case of an increasing size. We have developed actuatable flexible structures. LayerCAKE is a laminated open-cell and closed-cell foam structure, where cell foam is a lightweight and flexible material that can be used to realize large actuatable flexible structures. LayerCAKE is actuated using the concept that open- and closed-cell foams contract differently when they are vacuumed. In this paper, the design of a large LayerCAKE mechanism is described and tested. A large actuatable flexible structure of size approximately 1250 mm that bends in a vertical direction was realized.

Hydrogen production by water splitting is expected to be a significant power source in future because of its cleanness and environment-friendliness. In this study, an actuator driven by hydrogen produced by water splitting is studied and a hydrogen-induced stress model for a bimorph-type hydrogen actuator is developed. From the examination of the soft actuator having electrodes made of polyvinyl chloride with palladium electrode (Pd-PVC), the stress and bending moment induced by hydrogen absorption during water splitting are quantitatively evaluated. The results show that the thickness of the palladium electrode affects the mechanical performance of the Pd-PVC actuator, with the thinner palladium electrode showing a larger bending moment and tip displacement. A simple mechano-electro-chemical coupling equation is proposed to describe the relationship between bending moment, stress, and the electric charge used for water splitting. A palladium electrode soft actuator can work as a hydrogen generator/storage mechanism and as a mechanical actuator, and it can be useful for the power source of small systems or micro- or nano-devices.

Electromagnetic (EM) microwave stealth soft robots are in urgent need in military application. Photothermal soft actuators with photomechanical energy conversion have attracted significant interest owing to their remote control, flexibility, and contactless operation. The innovative combination of an electromagnetic microwave absorption (EMA) function with a photothermal actuator paves the way for this aspect. Here, a composite with unique dual three-dimensional foam is fabricated based on graphene and hollow carbon spheres (HCSs). When exposed to 1 sun illumination, the temperature could increase to 50 °C within 1 min and plateaus at 80 °C for hollow carbon spheres-graphene foam-polydimethylsiloxane (HCSs-GF-PDMS), which shows great photothermal performance. A wormlike crawling robot has been constructed based on this composite material, which could move forward under only 1 sun illumination. Remarkably, the EM stealth could be successfully realized because the composite material exhibits great EMA performance with a minimum reflection loss of -56.99 dB at a thickness of 2.5 mm, and the maximum effective absorption bandwidth is 8.65 GHz. In addition, the HCSs-GF exhibits hydrophobic and lightweight functions as well, which lighten the weight of soft robots and lead to self-cleaning and energy saving. This work provides a promising direction of multifunctional EM stealth soft robots.

The unique functional properties of nickel-titanium Shape Memory Alloys (SMA) enable them to be used as actuators. This research paper demonstrates theoretically and experimentally the feasibility of using SMA in smart tires for a mobile robot. The design procedure for SMA as a coil spring actuator for a soft deformable wheel is described. The primary focus is the mechanical modeling, manufacturing, and system dynamics of a soft deformable wheel. The 3D printed soft tire exploits the capabilities of the SMA actuation using a voltage signal. The printed components are activated and integrated with electromechanical circuit for wireless communication system. The performance of the force feedback control system is evaluated at different operating conditions to demonstrate the shape-changing characteristic of the smart tire. The developed prototype is designed to propel forward and backward on flat and uneven surface. The experimental results obtained demonstrate the potential of SMA as soft actuators, its benefits and limitations as flexible systems.

The application of soft pneumatic actuators is typically hindered by the low strength and slow response speed caused by their intrinsic material limitation and unstressed stable form. In this work, we present a design strategy for improving the performance and response speed for Pneu-Nets actuators by incorporating adjustable elastic components to form the elastic composite pneumatic actuator (ECPA). The elastic energy storage of the elastic component is implemented to enhance the capability and speed up the response of ECPA and pre-bend the actuator. Due to the design principle, the fully-flexible ECPA is easy to manufacture and regulate. Theoretical modeling and experiments are implemented to reveal the fast response characteristics and adjustable mechanical characteristics of ECPA. Experimental results show that the deflation response speed of ECPA is increased by at least 3.1 times with the action of elastic components, what is more, the stiffness of ECPA is increased by 22 times. Based on the ECPA, two kinds of locomotion robots including a running robot (runs at an average locomotion speed of 6.3 BL/s (body lengths, BL)) and an underwater swimming robot (achieves an average speed of 1.1 BL/s) are designed. The fast-moving robots both demonstrate high-speed mobility because of the rapid response and high strength of ECPA.

The cooperation of torsion and bending can improve the flexibility in the motion process especially in complex and narrow space. There is few research about torsion in soft actuators until now, most of them focus on bending and elongation. Moreover, motion form is often single so that it is hard to imply complex tasks. In this paper, inspired by the structure features of parallel robot, we propose a new cable-driven soft actuator whose driven cable is arranged imitating the supporting rod of parallel robot. This actuator can implement clockwise and anti-clockwise torsion and two modes bending motion respectively. The maximum torsion angle can realize 45° and the maximum bending angle is 90°. First, we introduce the design principle and fabrication process. After that, we utilize conservation of energy method and force decomposition analysis to establish the kinematics of actuator, in addition, based on that, we conduct the parameters optimization. Finally, we design an experiment platform to conduct experiments and make the contrast with theory. This soft actuator can highly improve the flexibility in soft robotics, especially in wrist joint imitation.

There are two corresponding authors who have contributed to this letter, yet only one of them has been mentioned as the corresponding author in the original letter. As a result, “Ki-Uk Kyung” was added to footnote as a co-corresponding author. The changes have been reflected as follows.

A physical prototype of a human esophagus has been developed for reproducing the human swallowing process with the aim of studying various disorders that impair its function as well as for the development of new foods and technologies for their treatment. Several studies related to the peristalsis phenomena have been conducted in recent years by studying the effect of different parameters defining the peristaltic wave. Mathematical models have been developed to investigate the impact of an integral and a non-integral number of waves during the swallowing of food stuff such as jelly, tomato puree, among others. Swallowing through the esophagus has not only been studied numerically but also reported by using a pneumatic soft actuators. In the present work, the development of a soft actuator mechanism to reproduce the peristaltic wave as the one reported by F.J. Chen et. al. 2014 is described. Such a mechanism consists of a rubber structure that contains an array of chambers actuated by pressurized air to generate the peristaltic wave. The final chamber shape was determined after an iterative process, which involves the elastomer properties, different chamber shapes, finite element analysis and image processing. The characterization of the developed peristaltic mechanism was made by correlating a theoretical study of swallowing peristaltic model and the waveform obtained from the X-ray radiography analysis as the mechanism is actuated. As result, the soft actuator mechanism can reproduce a peristaltic waveform with a correlation coefficient near to 0.9 with respect to the mathematical model reported in literature. In addition, the manufacturing process based on additive manufacturing technologies is also presented.