Zero‐Power Shape Retention in Soft Pneumatic Actuators with Extensional and Bending Multistability

The soft robotics field investigates biological bodies’ movements to develop soft actuation with similar behavior seen in nature. The skeletal muscles’ movements are vastly mimicked in soft actuators; however, the contractions of smooth muscles are overlooked in soft robotics. Smooth muscles provide peristaltic contractions to the digestive system, such as the stomach, and their design challenges the limits of soft robot development that simulates digestive organs. In this article, we present a novel, bellows-driven soft pneumatic actuator (SPA) with a self-sensing capability that generates linear displacement to simulate a smooth muscle segment in a stomach. This SPA is proposed as a solution for applications such as stomach simulators. The SPA concept, design, fabrication, creep model, and experimental validation are presented in this article. A lumped viscoelastic model presents the actuator's modeling to predict the SPA's displacement from a known applied pressure. The model is successfully validated, which resulted in a maximum displacement of 20.0 mm with a displacement error of 3%. A sensory system embedded in the SPA measures the displacement, and it is found that a force of 0–8.0 N is produced. A polynomial equation calibrates the sensor readings, with a displacement error of 5%. The results show the SPA's capability as a linear soft actuator that can generate a deformation like a smooth muscle segment. To simulate a circular contraction from a stomach with the SPA, we install multi-SPAs in a ring frame that performs contractions. Although the proposed SPA is specifically designed to mimic the smooth muscle, the ring actuator's contractions can be used for other applications such as gripping soft objects.

Drawing on the driving mechanism of biological muscles and combining the nonlinear hyperelastic characteristics of silicone rubber, a multi-degree-of-freedom pneumatic soft bionic actuator is designed, which can be used as the executing mechanism for soft robots and robotic arms. Using response surface analysis and numerical simulation algorithms, the optimal combination of structural dimensions parameters is determined with the maximum bending and torsion angles output by the actuator as the optimization objectives. Based on the idea of flexible mechanism Piecewise Constant Curvature (PCC) modeling, the kinematics equation of the actuator is derived. Analyze the equivalent motion structure of the actuator and establish a dynamic model of the actuator based on the Lagrange method. The physical model of the actuator is manufactured using rapid prototyping technology. Finally, experimental testing and analysis are conducted on the physical model to obtain the motion and dynamic characteristics curves and empirical formulas of the actuator, which are compared with theoretical and simulation results to verify that the pneumatic soft bionic actuator is feasible and effective. The above research methods, processes, and results can provide reference and inspiration for the research and implementation of pneumatic and hydraulic soft robots and gripping actuators for soft robotic arms.

Design and implementation of variable inclined air pillow soft pneumatic actuator suitable for bioimpedance applications

With the development of advance materials, soft robotics is being widely applied in various industrial manufacturing chains. One of the prominent applications of soft robotics is soft pneumatic actuator (SPA) gripper which is an essential part in the food industry due to their advantages like high compliance and human-friendly interaction. This study presents a systematic approach to analyze a SPA gripper used in the food industry. The behaviors of SPA gripper are analyzed by using image processing technology. Firstly, the structural geometry of soft gripper model controlled by pneumatic actuators is suggested. Moreover, the geometrical parameters like chamber thickness of the soft gripper is optimized by the combination of finite element method (FEM) modeling and experiment. The working characteristics of the chosen concept based on the chamber parameter of this soft SPA gripper are analyzed.

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.

Soft pneumatic actuator with strain-limiting layers has played an important role in soft robotics in the last decades. However, limited by their pre-designed and permanent strain-limiting layers, their motion pattern is usually single. Here, we proposed a soft pneumatic actuator with multiple motion patterns based on length-tuning strain-limiting layers. We integrated 4 cable-based strain-limiting layers into a 3D printed soft pneumatic actuator. A cable locking system is proposed to lock the cables as strain-limiting layers. The system is actuated by a small fabric balloon and can provide up to 79 N blocking force. With a rotatory sensor, it can also monitor the actual length of the cable. The soft pneumatic actuator can achieve omnidirectional bending and extension by regulating the state of the 4 cable locking systems. By experiments, we verify the work principle of cable locking system. The actuator here can also vary its stiffness from 6 N/m to 97 N/m by antagonism.

Printed silicone pneumatic actuators for soft robotics

The modeling and design of soft pneumatic actuators is a key direction in soft robotics research, aiming to develop flexible and efficient actuators to adapt to complex applications. However, theoretical modeling studies for multi-degree-of-freedom actuators are less frequent and still challenging. In this paper, a multi-degree-of-freedom soft pneumatic actuator (MDoF SPA) composed of multiple oblique chamber actuator units and a hollow cylinder structure is designed and fabricated. It could realize bending motion in the same module, especially twisting motion in both directions. Based on the Yeoh model, not only the elastic strain energy density function of the inflated actuator unit but also the elastic strain energy density function of an equivalent bow tie hollow column has been considered. The theoretical model of the MDoF SPA is established using the virtual work principle. The effectiveness of the theoretical model is verified by comparing it with the finite element analysis and experimental results. The effects of the angle of the oblique chamber and pressure on the deformability, bending force, and torque of the MDoF SPA are discussed. Finally, the MDoF SPA is applied to the bionic turtle shoulder joint and soft robotic arm manipulation scenes. This study provides theoretical support for the design of soft robots and expands the application potential of soft pneumatic actuators.

Emerging classes of soft robotics with flexible actuation, intelligent sensibility, and biomimetic functionality are driving significant advances in academic researches and commercial applications. Such new generation robotics relies heavily on important breakthroughs in soft matter engineering and flexible actuation systems. Unlike conventional rigid robots, soft robots generally have unique sporting styles and manufacturing strategies. Recently, a series of newly developed soft materials—gallium‐based liquid metals (LMs) are found to display dramatical roles in making soft machines and robotics with their unusual properties in soft robotic actuation and self‐driven field. With superior merits of both high stretchability and electroconductivity over conventional soft materials, LM is increasingly innovated as flexible sensors and actuators in constructing intelligent soft robots. Typical advances in LM enabled soft machines and robotics are summarized and interpreted, herein, with special focus on the driving principles of the LM objects, the preparation methods of LM flexible electronics for making soft robots, and the applications of LM in biomedicines and intelligent robots, together with the consideration of key challenges facing LM‐based soft robotics and its future prospects.

Soft robotics technology creates new ways for legged robots to interact with and adapt to their environment. In this paper we develop i) a new 2-degree-of-freedom soft pneumatic actuator, and ii) a novel soft robotic hexapedal robot called SoRX that leverages the new actuators. Simulation and physical testing confirm that the proposed actuator can generate cyclic foot trajectories that are appropriate for legged locomotion. Consistent with other hexapedal robots (and animals), SoRX employs an alternating tripod gait to propel itself forward. Experiments reveal that SoRX can reach forward speeds of up to 0.44 body lengths per second, or equivalently 101 mm/s. With a size of 230 mm length, 140 mm width and 100 mm height, and weight of 650 grams, SoRX is among the fastest tethered soft pneumatically-actuated legged robots to date. The motion capabilities of SoRX are evaluated through five experiments: running, step climbing, and traversing rough terrain, steep terrain, and unstable terrain. Experimental results show that SoRX is able to operate over challenging terrains in open-loop control and by following the same alternating tripod gait across all experimental cases.

The field of soft robotics has a wide array of applications, particularly in human-robotic interaction, from medical devices to assembly technology. In this paper, we introduce a novel design for a soft bi-directional pneumatic actuator inspired by the principles of origami. The actuator integrates a variable stiffness application using a layer jamming mechanism (LJM). LJM utilizes the effects of negative pressure on thin layers of material, providing rigidity. Incorporated into an origami bellows structure, the negative pressure causes both contractile action and stiffness, while extensive action is caused by an internal pneumatic chamber, allowing for contractile and extensive force application. Furthermore, the variable stiffness integration improved tensile force application threefold, resistance to outside linear force tenfold, and doubled sheer force resistance. The proposed origami-inspired bi-directional soft pneumatic soft actuator has immense potential to be implemented in complex biomedical applications in the near future.

Silicone rubber is widely used in various soft robots, sensors, and actuators. One of the most popular fabrication processes for silicone rubber is molding, which can easily duplicate three-dimensional (3D) shapes using a mold. Among the molding techniques, vacuum molding is a useful approach for preventing defects in molded parts. However, during the vacuum molding process, handling objects in a vacuum is challenging, requiring the mold to be carefully designed to prevent air bubble entrapment without manipulating the silicone rubber pouring point or the mold. In this study, to address these challenges, we propose an in-vacuum silicone rubber forming process. This process allows the silicone rubber pouring point to be controlled in a vacuum using a five-bar parallel link manipulator. This manipulator can be easily installed with only two rotational rods, typically employed as mixing rods within the chamber, facilitating efficient molding processes such as multi-part fabrication with minimal silicone rubber waste without the need for special mold designs. We validate the effectiveness of this process by molding cylindrical structures with diameters ranging from 1.2 to 5 mm and three types of liquid silicone rubbers with viscosities from 3 to 20 Pa·s. Compared to conventional methods—standard molding and vacuum molding, our proposed approach could successfully mold all cylinders without voids or air bubbles. Additionally, the applicability of this method to soft robotics was demonstrated through two applications using major soft actuators, pneumatic actuator and dielectric elastomer actuator (Non-standard abbreviation: DEA—Dielectric Elastomer Actuator), for soft robotics.

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.

Three-dimensional cellular tissue reproduces the structure and function similar to the tissues in the body. So far, as a means for the formation and maturation of three-dimensional cellular tissues, various mechanical stimuli have been applied to cells. Compression by mechanical actuators is a popular method for applying mechanical stimulation to cells. However, the use of linear or rotary actuators limits the direction of compressive stimulation to one axis and requires the cell to be adhered to a scaffold for fixation. Here, we propose a method to form three-dimensional cellular tissue cultured by a hydrogel microwell in a pneumatic soft actuator as a hybrid soft actuator. The hydrogel microwell deformed by the pneumatic soft actuator envelopes and three-dimensionally compresses the cells in the hydrogel microwell even shortly after cell seeding due to no need to fix the cells on the scaffold. In this study, ATDC5 cells, which are a mouse chondrogenic progenitor cell line having high activity to compressive stimuli, were cultured to apply enveloping compressive stimulation to the cells. By applying compressive stimulation to the cells in the hydrogel microwell using the pneumatic soft actuator, the formation of cellular tissue was promoted at an early stage before the cells began to adhere to each other. Moreover, the cellular tissue compressed by the pneumatic soft actuator expressed Sox9 and collagen II as well as the control without compressive stimuli. This proposed culture with the pneumatic soft actuator is a promising three-dimensional culture method capable of compressing cells, which can be applied for regenerative medicine and drug screening.

Conventional robots are constructed with rigid parts and materials, restricting their ability to deform freely and adapt to the external environment. Performing tasks such as handling delicate materials and navigating narrow pathways is challenging for these typical robots made of stiff materials. However, there is a growing demand for such functions in various industries. Recent advances in soft robotics have garnered considerable attention as solutions to these challenges. Soft robotic systems in various forms present a systematic solution for performing unique tasks. The goal of soft robotics research is to develop advanced technologies, incorporating innovative robotic mechanisms based on soft materials and structures to enhance adaptability. Soft robots find broad applications in diverse fields, including industry, healthcare, and field exploration. Soft component technology plays a crucial role in configuring soft robots. Soft actuators introduce new types of motion and operation mechanisms, while soft sensors measure the deformation of the actuators with a tiny stiffness change. These advancements in soft actuators and sensors encourage researchers to explore new robotic designs and applications. Additionally, the component technology enables the integration of soft and typical robots into hybrid B Youngsu Cha