Soft Pneumatic Actuators Research Articles

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%.

Structural optimization and parameter investigation of trapezoidal shape soft pneumatic actuator

Abstract This study investigates the effects of actuator design parameters on the performance of developed trapezoidal shaped soft pneumatic actuator, optimizes its geometric structure using the finite element method and validates its performance experimentally. To optimize the soft pneumatic actuator, the effects of structural parameters such as wall thickness, gap between the adjacent chambers, passive layer thickness, width of inside chamber and the bending angle of the actuator were evaluated. Finite Element Analysis is used to determine the displacement variation of actuator with different levels of applied pressures. A Global Analysis of Variance was conducted to determine the influence of variables affecting the displacements of soft pneumatic actuator was determined. The ANOVA results, a geometric actuator with a wall thickness of 1.5 mm, gap between chambers of 4 mm, passive layer thickness of 2 mm and the width of inside chamber of 4 mm is recommended for the actuator to be achieve maximum bending angle. The proposed actuator model can be used to select the suitable actuator for grasping soft objects without deformation. In addition, experiment was conducted to correlate the results with finite element analysis data.

Directional soft jumper by harnessing asymmetric snapping of a semi-open shell

Precise control of the jumping direction and trajectory of soft robotics poses a challenge due to their large deformation and low stiffness. In this paper, we propose a pneumatic soft actuator consisting of an inward semi-spherical shell with a pre-existing T-shaped incision, which exhibits asymmetric snapping-through buckling under an increasing internal pressure. During the dynamic snapping, the shell deforms rapidly, resulting in an asymmetric, inclined impact with the ground. The impact force drives the soft actuator to jump in a controllable direction, and the adopted semi-open pneumatic system greatly improves the efficient utilization of air ejection energy. This design not only enhances the jumping performance, but also allows the control of the trajectory through adjusting the air pressure. Our experiments demonstrate that the actuator can achieve various jumping functions, for examples, to jump over obstacles of varying heights and depths, to execute rapid and continuous locomotion, and even to escape from a deep bottle. This work offers a paradigmatic idea for designing highly maneuverable and controllable soft robots.

Multistable Composite Laminate Grids as a Design Tool for Soft Reconfigurable Multirotors

Adaptive‐morphology multirotors exhibit superior versatility and task‐specific performance compared to traditional multirotors owing to their functional morphological adaptability. However, a notable challenge lies in the contrasting requirements of locking each morphology for flight controllability and efficiency while permitting low‐energy reconfiguration. A novel design approach is proposed for reconfigurable multirotors utilizing soft multistable composite laminate airframes. These airframes show kinematically determinate morphologies corresponding to multiple minima in their elastic potential energy landscape. By varying design parameters, the methodology allows for tuning the energy landscape characteristics governing each morphology's structural stability and reconfiguration energetics. The airframe, composed of multistable composite laminate grids, is optimized to maximize rigidity under flight loads and minimize reconfiguration work. The 130‐g reconfigurable multirotor design demonstrates self‐locking properties in an open and a folded configuration, enabling a 48% reduction in width‐span without compromising stability during flight. Soft pneumatic actuators, actuated using a tethered compressed air supply, enable reversible reconfiguration on the ground between open and folded configurations. The design resolves the conflicting requirements of high‐stiffness to lock each flight configuration and low‐actuation work for reconfigurability. By exploiting soft yet multistable structures, the approach combines the stability observed in rigid‐linked reconfigurable multirotors with the low‐effort reconfigurability of soft multirotors, offering new methods for designing adaptive‐morphology multirotors.

Soft-Rigid Hybrid Revolute and Prismatic Joints Using Multilayered Bellow-Type Soft Pneumatic Actuators: Design, Characterization, and Its Application as Soft-Rigid Hybrid Gripper

Soft-Rigid Hybrid Revolute and Prismatic Joints Using Multilayered Bellow-Type Soft Pneumatic Actuators: Design, Characterization, and Its Application as Soft-Rigid Hybrid Gripper

A new design and analysis of low-profile soft rotary pneumatic actuator for enhanced rotation and torque

Soft actuators producing bending motions have gained significant attention for their advantages in mimicking the properties and movements of human muscles. However, the research on soft rotary actuators has yet to keep pace with other soft actuators. This paper makes two key contributions to the design and modeling of these actuators. First, we introduce a novel design for a soft rotary pneumatic actuator. This design outperforms existing cylindrical shaped soft actuators, especially in terms of torque. Second, we present an analytical model based on finite deformation. This model accurately describes the relationship between rotational movement and corresponding torque. The accuracy of this model is validated through Finite Element Method (FEM) simulations and corresponding tests. By providing a mechanically efficient design and a highly accurate analytical model, this work offers a comprehensive solution for the development of new soft pneumatic actuators.

Reconfigurable, Transformable Soft Pneumatic Actuator with Tunable Three-Dimensional Deformations for Dexterous Soft Robotics Applications.

Numerous soft actuators based on pneumatic network (PneuNet) design have already been proposed and extensively employed across various soft robotics applications in recent years. Despite their widespread use, a common limitation of most existing designs is that their action is predetermined during the fabrication process, thereby restricting the ability to modify or alter their function during operation. To address this shortcoming, in this article the design of a Reconfigurable, Transformable Soft Pneumatic Actuator (RT-SPA) is proposed. The working principle of the RT-SPA is analogous to the conventional PneuNet. The key distinction between the two lies in the ability of the RT-SPA to undergo controlled transformations, allowing for more versatile bending and twisting motions in various directions. Furthermore, the unique reconfigurable design of the RT-SPA enables the selection of actuation units with different sizes to achieve a diverse range of three-dimensional deformations. This versatility enhances the RT-SPA's potential for adaptation to a multitude of tasks and environments, setting it apart from traditional PneuNet. The article begins with a detailed description of the design and fabrication of the RT-SPA. Following this, a series of experiments are conducted to evaluate the performance of the RT-SPA. Finally, the abilities of the RT-SPA for locomotion, gripping, and object manipulation are demonstrated to illustrate the versatility of the RT-SPA across different aspects.

A Methodology for the Mechanical Design of Pneumatic Joints Using Artificial Neural Networks

The advent of collaborative and soft robotics has reduced the mandatory adoption of safety barriers, pushing human–robot interaction to previously unreachable levels. Due to their reciprocal advantages, integrating these technologies can maximize a device’s performance. However, simplifying assumptions or elementary geometries are often required due to non-linear factors that identify analytical models for designing soft pneumatic actuators for collaborative and soft robotics. Over time, various approaches have been employed to overcome these issues, including finite element analysis, response surface methodology (RSM), and machine learning (ML) algorithms. Based on the latter, in this study, the bending behavior of an externally reinforced soft pneumatic actuator was characterized by the changing geometric and functional parameters, realizing a Bend dataset. This was used to train 14 regression algorithms, and the Bilayered neural network (BNN) was the best. Three different external reinforcements, excluded for the realization of the dataset, were tested by comparing the predicted and experimental bending angles. The BNN demonstrated significantly lower error than that obtained by RSM, validating the methodology and highlighting how ML techniques can advance the prediction and mechanical design of soft pneumatic actuators.

Omnidirectional soft pneumatic actuators: a design and optimization framework.

Soft pneumatic actuators (SPAs) play a pivotal role in soft robotics due to their unique characteristics of compliance, flexibility, and adaptability. There are plenty of approaches that examine the modeling parameters of SPAs, aiming to optimize their design and, thus, achieve the most advantageous responses. Current optimization methods applied to SPAs are usually performed individually for each design parameter without considering the simultaneous effect all parameters can have on the output performance. This modeling shortcoming is essential to be addressed since customized SPAs are used in a variety of applications, each with different output requirements. This study provides a generalized design optimization framework for modeling the SPA performance for their motion profiles, the produced strain energy while being deformed, and their stiffness characteristics. Utilizing experimentally validated finite element methods, all geometrical and material parameters of the models are investigated in response surface methodology optimization using the central composite design approach. The results showcase the entire design space of omnidirectional SPAs, along with their output performance, providing guidelines to the end user for design optimization. The offering of this modeling process for SPAs can be adapted to the demands of any potential application and ensure the best performance with respect to the required output responses.

PneumaOCT: Pneumatic optical coherence tomography endoscopy for targeted distortion-free imaging in tortuous and narrow internal lumens.

The complex anatomy of internal luminal organs, like bronchioles, poses challenges for endoscopic optical coherence tomography (OCT). These challenges include limited steerability for targeted imaging and nonuniform rotation distortion (NURD) with proximal scanning. Using rotary micromotors for distal scanning could address NURD but raises concerns about electrical safety and costs. We present pneumaOCT, the first pneumatic OCT endoscope, comprising a steerable catheter with a soft pneumatic actuator and an imaging probe with a miniature pneumatic turbine. With a diameter of 2.8 mm, pneumaOCT allows for a bending angle of up to 237°, facilitating navigation through narrow turns. The pneumatic turbine enables adjustable imaging speeds from 51 to 446 revolutions per second. We demonstrate the pneumaOCT in vivo imaging of mouse esophagus and colon, as well as targeted and distortion-free imaging of peripheral bronchioles in a bronchial phantom and a porcine lung. This advancement substantially improves endoscopic OCT for navigational imaging in curved and narrow lumens.

Soft pneumatic actuators for pushing fingers into extension

BackgroundCompliant pneumatic actuators possess many characteristics that are desirable for wearable robotic systems. These actuators can be lightweight, integrated with clothing, and accommodate uncontrolled degrees of freedom. These attributes are especially desirable for hand exoskeletons, where the soft actuator can conform to the highly variable digit shape. In particular, locating the pneumatic actuator on the palmar side of the digit may have benefits for assisting finger extension and resisting unwanted finger flexion, but this configuration requires suppleness to allow digit flexion while retaining sufficient stiffness to assist extension.MethodsTo meet these needs, we designed an actuator consisting of a hollow chamber long enough to span the joints of each digit while sufficiently narrow not to inhibit finger adduction. We explored the geometrical design parameter space for this chamber in terms of shape, dimensions, and wall thickness. After fabricating an elastomer-based prototype for each actuator design, we measured active extension force and passive resistance to bending for each chamber using a mechanical jig. We also created a finite element model for each chamber to enable estimation of the impact of chamber deformation, caused by joint rotation, on airflow through the chamber. Finally, we created a prototype hand exoskeleton with the chamber parameters yielding the best outcomes.ResultsA rectangular cross-sectional area was preferable to a semi-obround shape for the chamber; wall thickness also impacted performance. Extension joint torque reached 0.33 N-m at a low chamber pressure of 48.3 kPa. The finite element model confirmed that airflow for the rectangular chamber remained high despite deformation resulting from joint rotation. The hand exoskeleton created with the rectangular chambers enabled rapid movement, with a cycle time of 1.1 s for voluntary flexion followed by actuated extension.ConclusionsThe developed soft actuators are feasible for use in promoting finger extension from the palmar side of the hand. This placement utilizes pushing rather than pulling for digit extension, which is more comfortable and safer. The small chamber volumes allow rapid filling and evacuation to facilitate relatively high frequency finger movements.

Human-Hand Inspired Elastomeric Soft Pneumatic Actuators: Mapping the Research Landscape and Prospects

Human-Hand Inspired Elastomeric Soft Pneumatic Actuators: Mapping the Research Landscape and Prospects

Characterization of fatigue behavior of 3D printed pneumatic fluidic elastomer actuators

Soft robots have gained significant interest due to their high flexibility and adaptability to various working conditions. Recent advancements in engineering and innovative materials have enabled the design and production of sophisticated soft robotic systems with enhanced capabilities. This study aims to evaluate the fatigue behavior of bellow-type pneumatic soft actuators fabricated through fused filament fabrication (FFF) using thermoplastic polyurethane (TPU), compared to silicone rubber cast actuators. The actuators were equipped with resistive flex sensors to monitor bending motion, and fatigue tests were performed with cycles of inflation and deflation until failure. Results showed that 3D printed TPU actuators could withstand a significant number of cycles before failure, with an average of 6410 cycles at 3 bar pressure, compared to 3439 cycles at 1 bar pressure for the silicone actuators. The study identified a set of fabrication parameters that positively affect the durability of TPU actuators, providing valuable insights for replicating these results. Additionally, the study established a plausible range of utilization for 3D-printed FFF actuators in terms of the number of cycles they can endure, offering critical data for engineers and designers to make informed decisions about the design and application of these actuators in various practical scenarios. The findings demonstrate the potential of FFF for producing durable, long-lasting pneumatic soft actuators.