Soft Pneumatic Actuators Research Articles

Investigation of uni- and bi-directional soft pneumatic actuators and its implication using rapid prototyping

Abstract In the age of automation and robotics, pneumatic grippers play a crucial role in material handling across diverse industrial sectors. This study explores the design and performance of uni- and bi-directional pneumatic grippers, which provide enhanced versatility and multi-directional gripping capabilities, using a rapid prototyping approach to address modern manufacturing needs. Through finite element analysis and experimental testing, the functionality of the gripper is evaluated, with a focus on hyperelastic materials like thermoplastic polyurethane. Three mesh techniques—automatic, tetrahedral, and hex-dominant—are analyzed, with the hex-dominant mesh proving the most effective for all models. Pressures up to 100 kPa, applied in 25 kPa increments to simulate real-world conditions, assessing deformation in both the uni- and bi-directional gripper mechanisms. Key design optimizations based on FE analysis include: a 1 mm gap between the chambers, which has shown an optimal deformation improvement of 109%, and a wall thickness ranging from 0.5 to 1 mm, which balances flexibility while minimizing deformation. In the bi-directional configuration, a chamber height of 4 mm achieves faster deformation with a maximum of 387.86%. Additionally, a 1 mm mid-layer deforms more rapidly, indicating that a thinner mid-layer enhances deformation and increases flexibility. The optimized Model-5, with refined geometry, successfully resolved issues of air leakage and printing defects, demonstrating effective bi-directional gripping capabilities and improved flexibility. The results validate the effectiveness of the design and analysis approach used in this study. These findings underscore the potential of bi-directional pneumatic grippers to transform material handling into industrial applications, offering significant improvements in adaptability and efficiency.

Design and validation of a programmable dual-tunnel soft pneumatic origami actuator with a large maximum shrinkage rate for reciprocating motion

Abstract. Soft actuators have attracted significant research in various domains owing to their flexible motion characteristics. However, the applications of soft actuators are constrained by their low force-to-weight ratio and maximum shrinkage rate, which is the ratio of the maximum stroke to the extreme length of the actuator, considerably augmenting the driving energy and occupied area. This paper presents a novel dual-tunnel soft pneumatic origami actuator capable of providing a large maximum shrinkage rate for reciprocating motion. The inner tunnel is constructed by the origami mechanism chamber, and the outer tunnel is formed by the origami mechanism in conjunction with the outer soft skin. A programmable design method for the proposed actuator is presented, based on its geometric parameter model and stiffness model. A kinematics model is developed to analyze the motion behavior and characteristics of the actuator's reciprocating motion. The prototype is fabricated using lightweight materials, such as oriented polypropylene and hard cardboard, on which tensile and load experiments are conducted. The results verify the motion characteristics of the soft actuator and the accuracy of the model. Compared to other linear actuators, the soft origami actuator is lightweight (weighing 5 g), has a large maximum shrinkage rate (61 %) and boasts a force-to-weight ratio of 600. The design demonstrates the extensive application potential of soft actuators with the origami mechanism.

Machine Learning Models for Assistance from Soft Robotic Elbow Exoskeleton to Reduce Musculoskeletal Disorders

Musculoskeletal disorders are very common injuries among occupational and healthcare workers. These injuries are preventable in many scenarios using exoskeleton-based assistive technology. Soft robotics initiates an evolution in exoskeleton devices due to their safe human interactions, ergonomic design, and adaptive characteristics. Despite their enormous advantages, it is a challenging task to model and control soft robotic devices due to their inherent nonlinearity and hysteresis. Learning-based approaches are becoming more popular to overcome these limitations. This work proposes an approach to estimate the pressure input for a pneumatically actuated soft robotic elbow exoskeleton to assist occupational workers to avoid musculoskeletal disorders. An elbow exoskeleton design made up of modular pneumatic soft actuators is discussed, which helps to flex/extend an elbow joint. Machine learning (ML) approaches are used to develop a relationship between the air pressure, the bending angle of the elbow, and the percentage of the weight of the arm to be assisted by the exoskeleton. The most popular and widely used regression-based ML approaches are applied and compared in terms of accuracy and computation cost. Further, a modified KNN (K-Nearest Neighbor) approach is proposed, which outperforms the accuracy of other approaches.

Tri-Prism Origami Enabled Soft Modular Actuator for Reconfigurable Robots.

Soft actuators hold great potential for applications in surgical operations, robotic manipulation, and prosthetic devices. However, they are limited by their structures, materials, and actuation methods, resulting in disadvantages in output force and dynamic response. This article introduces a soft pneumatic actuator capable of bending based on triangular prism origami. The origami creases are crafted by utilizing fabrics to gain swift response and fatigue-resistant properties. By connecting two actuators in series, combined motions including extension and diversified compound bending can be achieved, facilitating control in complex scenarios. After modularizing the soft actuator via mortise and tenon structures, several actuators can be programmed to execute a variety of intricate tasks by adjusting the timing sequences of their contraction and expansion. We showcase its applications in reconfigurable robots, and the results confirm that such a design is adequate for flexibly performing tasks such as soft gripping, navigational movement, and obstacle avoidance. These findings highlight the significance of our actuator in developing soft robots for versatile tasks.

Miniaturized Soft Pneumatic Actuator Matrix with Multiplexing Control

Soft robotics has recently attracted increasing attention due to its inherent softness and compliance. However, to fully realize their potential, it often requires numerous soft components and actuators. One major challenge for a large‐scale system is integration and miniaturization. In addition, for pneumatically controlled actuators, multiplexing is essential to reduce the tubing from the control valves. A miniaturized soft pneumatic actuator matrix (SPAM) with multiplexing control of crossing points by only control signals was realized by embedding two layers of interactive channels () in a soft material (PDMS) to form actuators () by cumulating both strokes and forces at the channel crossings, unlike piston‐based serially coupled gas‐springs that yield constant force. A SPAM prototype of actuators with control signals was studied. A SPAM was demonstrated in a tilting matrix and two coupled SPAMs were used in a pneumatic soft conveyor for planar manipulation. Its simplicity and size allow for future large‐scale integration in soft robotics.

Bioinspired Smart Triboelectric Soft Pneumatic Actuator-Enabled Hand Rehabilitation Robot.

Quantitative assessment for post-stroke spasticity remains a significant challenge due to the encountered variable resistance during passive stretching, which can lead to the widely used modified Ashworth scale (MAS) for spasticity assessment depending heavily on rehabilitation physicians. To address these challenges, a high-force-output triboelectric soft pneumatic actuator(TENG-SPA) inspired by a lobster tail is developed. The bioinspired TENG-SPA can generate approximately 20 N at 0.1MPa, providing sufficient stretching force for spastic fingers. The anti-interference, durability, and electrical output characteristics of the TENG-SPA under varying conditions-such as different air pressures, bending frequencies, and simulated spastic finger stretching-are explored, demonstrating TENG-SPA's ability to sense resistance during the stretching process. Furthermore, a TENG-SPA-enabled hand rehabilitation robot system integrated with the convolutional neural network (CNN) is further developed, which is tested in a clinical trial involving 15 stroke patients. The results have demonstrated that a classification accuracy for the levels of finger spasticity reaches 93.3% and the MAS scores predicted by the CNN regression model exhibit a strong linear relationship with the actual MAS (R2 = 0.8451, p <0.01). This study presents promising potential applications in digital rehabilitation medicine, human-machine interaction, biomedicine, and related fields.

A function online learning and prediction method for accelerating structural topology optimization and its application to pneumatic soft actuator

A function online learning and prediction method for accelerating structural topology optimization and its application to pneumatic soft actuator

Reconfigurable Soft Pneumatic Actuators with Metamaterial Reinforcements: Tunable Stiffness and Deformation Modes

Reconfigurable Soft Pneumatic Actuators with Metamaterial Reinforcements: Tunable Stiffness and Deformation Modes

Modeling and Control Experiments of a Fishtail-Like Pneumatic Soft Actuator

As the exploration of deep-sea resources continues, underwater actuators with conventional motors as the main building blocks can no longer meet the increasingly demanding needs. Inspired by bionics, researchers have started to work on underwater actuators with bionic structures. In this study, we designed and implemented a novel Fishtail-like Pneumatic Soft Actuator (FPSA). This innovative actuator configuration is inspired by the tail structure of Body and/or Caudal Fin (BCF) mode fish. The actuator's motion is achieved by controlling the expansion and contraction of the pneumatic soft muscles on both sides. And by constructing an experimental platform, we conducted an in-depth performance characterization, revealing the existence of a frequency-dependent nonlinear hysteresis characteristic of the FPSA. In order to accurately characterize this property, we built a dynamic model of the FPSA and successfully identified the uncertain parameters in the model by applying the nonlinear least squares method. The validation results show that the constructed model can accurately describe the nonlinear hysteresis characteristics of the FPSA. Finally, we successfully realized the high-precision trajectory tracking control of the endpoint of the FPSA using a PID controller. This result provides relevant ideas for the research of novel underwater bionic actuators.

Advanced vat photopolymerization 3D printing of silicone rubber with high precision and superior stability

Abstract Silicone rubber (SR) is a versatile material widely used across various advanced functional applications, such as soft actuators and robots, flexible electronics, and medical devices. However, most SR molding methods rely on traditional thermal processing or direct ink writing three-dimensional (3D) printing. These methods are not conducive to manufacturing complex structures and present challenges such as time inefficiency, poor accuracy, and the necessity of multiple steps, significantly limiting SR applications. In this study, we developed an SR-based ink suitable for vat photopolymerization 3D printing using a multi-thiol monomer. This ink enables the one-step fabrication of complex architectures with high printing resolution at the micrometer scale, providing excellent mechanical strength and superior chemical stability. Specifically, the optimized 3D printing SR-20 exhibits a tensile stress of 1.96 MPa, an elongation at break of 487.9%, and an elastic modulus of 225.4 kPa. Additionally, the 3D-printed SR samples can withstand various solvents (acetone, toluene, and tetrahydrofuran) and endure temperatures ranging from −50 °C to 180 °C, demonstrating superior stability. As a demonstration of the application, we successfully fabricated a series of SR-based soft pneumatic actuators and grippers in a single step with this technology, allowing for free assembly for the first time. This ultraviolet-curable SR, with high printing resolution and exceptional stability performance, has significant potential to enhance the capabilities of 3D printing for applications in soft actuators, robotics, flexible electronics, and medical devices.

A New Three-Dimensional Deformation Pneumatic Soft Actuator With Mutually Vertical PneuNets

A New Three-Dimensional Deformation Pneumatic Soft Actuator With Mutually Vertical PneuNets

Development of Rehabilitation Glove: Soft Robot Approach

This study describes the design, simulation, and development process of a rehabilitation glove driven by soft pneumatic actuators. A new, innovative finger soft actuator design has been developed through detailed kinematic and workspace analysis of anatomical fingers and their actuators. The actuator design combines cylindrical and ribbed geometries with a reinforcing element—a thicker, less extensible structure—resulting in an asymmetric cylindrical bellow actuator driven by positive pressure. The performance of the newly designed actuator for the rehabilitation glove was validated through numerical simulation in open-source software. The simulation results indicate actuators’ compatibility with human finger trajectories. Additionally, a rehabilitation glove was 3D-printed from soft materials, and the actuator’s flexibility and airtightness were analyzed across different wall thicknesses. The 0.8 mm wall thickness and thermoplastic polyurethane (TPU) material were chosen for the final design. Experiments confirmed a strong linear relationship between bending angle and pressure variations, as well as joint elongation and pressure changes. Next, pseudo-rigid kinematic models were developed for the index and little finger soft actuators, based solely on pressure and link lengths. The workspace of the soft actuator, derived through forward kinematics, was visually compared to that of the anatomical finger and experimentally recorded data. Finally, an ergonomic assessment of the complete rehabilitation glove in interaction with the human hand was conducted.

3D Printed Biodegradable Soft Actuators from Nanocellulose Reinforced Gelatin Composites

AbstractEco‐friendly materials are increasingly important for several applications due to growing environmental concerns, including in robotics and medicine. Within robotics, silicone‐based soft grippers are recently developed owing to their high adaptability and versatility allowing to deal with various objects. However, the soft grippers are difficult to recycle and may cause increased environmental impact. Here biodegradable soft pneumatic actuators reinforced by cellulose nanofibrils (CNF) distributed in a matrix of gelatin are presented. The results show that adding CNF enables 3D printability and provides tunable mechanical properties for the actuators. The actuator performance, with a bending angle of 80° and a blocked force of 0.1 N at 15 kPa, is comparable to state‐of‐the‐art mold‐casted pneumatic actuators from conventional silicone materials while being exclusively composed of non‐toxic, biodegradable materials and fabricated by additive manufacturing techniques. Moreover, the actuators exhibit self‐healing ability and enable object manipulation when formed in a gripper configuration. The mold‐free approach and achieved functionalities establish new opportunities for soft‐robotics, across various fields including healthcare, packaging, or even environmental monitoring. The performance of the gripper shows that CNF can be used in the creation of eco‐friendly high‐performance soft robots and contribute to the advancement of sustainable and green robotics.

Mechanical Design, Manufacturing, and Testing of a Soft Pneumatic Actuator with a Reconfigurable Modular Reinforcement

Soft actuators have enabled the growth of soft robotics, overcoming several drawbacks of rigid robotics by providing devices with many degrees of freedom and the ability to grasp, bend, move, jump, and more. The reconfiguration of the workspace is still a limitation of these actuators. Indeed, once the actuator is designed and developed, it is used for a specific task. This work presents a reconfigurable soft pneumatic actuator with a novel reconfigurable modular reinforcement. The latter is wrapped around an inner tube in silicone rubber and is made of components whose assembly can be configured based on the task. A formulation is identified by a hybrid approach based on finite element analysis and response surface methodology for predicting and designing the behavior of the actuator. The prototyping revealed the ease of fabrication and reconfigurability as the strength of this new actuator. The experimental tests demonstrated the feasibility of adopting the actuator as a finger in a gripper for handling and moving objects of different shapes, masses, and stiffness. Furthermore, the evaluated performance shows a good trade-off between mass, developed force, implementation time, easy reconfigurability, and cost-effectiveness.

Modeling and precise tracking control of spatial bending pneumatic soft actuators

In recent years, a variety of pneumatic soft actuators (PSAs) have been proposed due to the development of soft robots in biomimetic robots, medical devices, etc. At the same time, the modeling and control of PSAs remains an open question. In this paper, a spatial bending pneumatic soft actuator (SBPSA) modeling method based on the Prandtl–Ishlinskii (PI) model is proposed, and the inverse model is designed to compensate for hysteresis nonlinearity. Furthermore, an adaptive feedback controller combined with a hysteresis compensator is proposed for the precise control and tracking of SBPSAs. Finally, an experimental platform is built, and experimental results demonstrate the effectiveness of the proposed method for precise tracking.

Design and Applications of High Force Generation in 3D-Printed Pneumatic Artificial Muscles

Increasing the force generation and scalability of soft pneumatic actuators poses significant challenges in robotics applications, especially where high load capacities and precise control are required. This paper presents UniBPAM, a novel, scalable soft pneumatic actuator optimized through 3D printing to enhance force generation. By analyzing design parameters, such as the number of sides, height, and origami factor, UniBPAM achieved a 21.48% increase in force generation. Scalable across diameters from 36 to 144 mm, the actuator demonstrated the ability to lift up to 57 kg with 84.9% strain at larger scales. Additionally, the BiBPAM variant enables bidirectional actuation in robotic joints via motion control, which is realized through PID systems, making it suitable for various robotic applications.

Bending/force switching control of pneumatic soft actuator based on multi-sensor fusion

Abstract The soft actuator has unlimited freedom, and can realize the grasping of irregular or fragile objects. A pneumatic soft actuator is designed in this paper, which consists of a series of symmetrically distributed pneumatic chambers. The soft actuator consists of a top expansion layer composed of 20 chambers and a bottom restraint layer. The Yeoh model and the finite element method (FEM) were employed to analyze the bending of the soft actuator. To improve the tracking performance, a PID strategy of the endocrine system (ES-PID) based on the neuroendocrine thyroid hormone regulation mechanism was constructed to tune the bending deformation. To achieve steady and precise force control, a bending/force switching control algorithm based on multi-sensor fusion is designed to realize high control accuracy. The bending/force switching control strategy mainly consists of two feedback loops for bending control, a force control, and a switching control. In the experimental process, the bending control is the primary control, and the force control is the primary control when the switching condition is satisfied. In order to prevent the occurrence of a false switching action, a switching factor is constructed using the method of successive comparison of neighboring values. Finally, several experiments are carried out to verify the effectiveness and feasibility of the control algorithm.

Pump-Free Pneumatic Actuator Driven by the Vapor Pressure at the Gas-Liquid Equilibrium of Aqua Ammonia.

Currently, pneumatic soft actuators are widely used due to their impressive adaptability, but they still face challenges for more extensive practical applications. One of the primary issues is the bulky and noisy air compressors required to generate air pressure. To circumvent this critical problem, this work proposes a new type of air pressure source, based on the vapor pressure at the gas-liquid equilibrium to replace conventional air pumps. Compared with the previous phase transition method, this approach gains advantages such as generating gas even at low temperatures (instead of boiling point), more controllable gas output, and higher force density (since both ammonia and water contribute to the gas pressure). This work built mathematical models to explain the mechanism of converting energy to output action force from electrical energy and found the aqua ammonia system is one of the optimal choices. Multiple prototypes were created to demonstrate the capability of this method, including a pouch actuator that pushed a load 20,555 times heavier than its dead weight. Finally, based on the soft actuator, an untethered crawling robot was implemented with onboard batteries, showing the potentially extensive applications of this methodology.

Characterization of 3D printed multi-material soft pneumatic actuator

Characterization of 3D printed multi-material soft pneumatic actuator

Modular soft pneumatic actuator mimics elephant trunk locomotion

Robots support and facilitate tasks in all life fields. Soft robots specifically have the advantages of inherent compliance, safe interaction and flexible deformability. Soft pneumatic network (Pneu-Net) is a soft pneumatic actuator (SPA) composed of network of chambers that is actuated by pneumatic power. Soft Pneu-Net fits the human interface applications perfectly. In this paper, a bio-inspired modular based design for Pneu-Net actuator is developed. The actuator mimics the elephant trunk curling to be employed for rehabilitation of human hand fingers. The actuator is an integrated four Pneu-Net modules actuator which is attached to hand’s finger. The main introduced advantages in the new developed actuator are: providing four degrees of freedom (DoF) essential for finger’s motion by single compound actuator and developing a methodology for a modular soft Pneu-Net actuator that is efficiently reproducible. The actuator’s design is developed using computer aided design (CAD) software SOLIDWORKS. The design is simulated using finite element modeling (FEM) software ABAQUS. Fabrication process uses 3D printed molds. Soft material is molded in the 3D printed molds, forming actuator’s modules. Actuator’s modules are integrated by adhesion using the soft material. A proposed non-standard hyper-elastic material biaxial tension test is introduced as a quick material properties identification method that can produce a test table used for material identification in the FEM. Enhanced version for the actuator uses reinforcement fibers. Results show advances for the reinforced actuator, as it limits the unwanted actuator’s strain and deformation. The reinforced actuator shows improved energy efficiency reaches to 46%.