Pneumatic Soft Robots Research Articles

Framing responsive architecture with soft robots—the exploratory practice of soft pneumatic robotic architectural system

Inspired by intelligent skin, this research constructs a soft pneumatic robotic architectural system based on the interaction between inflatable material agents and the human body. It aims to provide flexibly changeable scene modes for dynamic inhabiting through responsive spatial performance. From the idea of the Fun Palace and the structure and performance spatial methodology to the proposal of responsive/soft architecture and relevant examples such as Furl and Robot Soft, the literature review provides the foundation and direction for the establishment of research experiments. The research methodology is based on structure and performance, oriented to explore soft material agents, link input information and output modules to realize the manifestation of human-space interaction and spatial performance and assemble the basic configuration of the system. As a result, a synergistic architectural interaction system like a media center that can provide a variety of adaptive space scenes is built, which can realize real-time perception and responsive control of the interactive process, and at the same time provide richness of scene performance beyond established architectural configurations, confirming the possibility of creating a behaviorally responsive architecture by integrating modularly morphing spaces, AI-sensing systems, and interaction technologies. This study explored responsive human settlements by expanding soft pneumatic robots in architecture. It can expand to fields such as machine cognition at the input level, further realize the real-time feedback system at the output level, and can evolve with the information interconnection of urban landscapes and residential communities in terms of spatial interaction. The work gives a convincing vision of architectural intelligence through soft robotics and is expected to continue to develop and bring more inspiring innovations with its integrated methods and connotations.

Soft Robot for Inspection Tasks Inspired on Annelids to Obtain Peristaltic Locomotion

Soft robotics is a rapidly advancing field that leverages the mechanical properties of flexible materials for applications necessitating safe interaction and exceptional adaptability within the environment. This paper focuses on developing a pneumatic soft robot bio-inspired in annelids or segmented worms. Segmentation, also called metamerism, increases the efficiency in body movement by allowing the effect of muscle contraction to generate peristaltic locomotion. The robot was built using elastomers by the casting technique. A sequence of locomotion based on two stages, relaxation and contraction, was proposed; the contraction stage is actuated by a vacuum pump. The locomotion performances are compared using different elastomers, such as Ecoflex 00-30, Dragon Skin 20, Mold Star 15 Slow, and Mold Star 30. Experimental tests were carried out inside a plexiglass pipe, 1 inch in diameter; a wide range of frequencies was tested for relaxation and contraction stages to evaluate the effect on the speed of the robot.

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

AbstractPower‐free shape retention enables soft pneumatic robots to reduce energy cost and avoid unexpected collapse due to burst or puncture. Existing strategies for pneumatic actuation cannot attain motion locking for trajectories combining extension and bending, one of the most common modes of operation. Here, a design paradigm is introduced for soft pneumatic actuators to enable zero‐power locking for shape retention in both extension and bending. The underpinning mechanism is the integration of a pneumatic transmitter and a multistable guider, which are programmed to interact for balanced load transfer, flexural and extension steering, and progressive snapping leading to state locking. Through theory, simulations, and experiments on proof‐of‐concept actuators, the existence of four distinct regimes of deformation is unveiled, where the constituents first interact during inflation to attain locking in extension and bending, and then cooperate under vacuum to enable fully reversible functionality. Finally, the design paradigm is demonstrated to realize a soft robotic arm capable to lock at desired curvature states at zero‐power, and a gripper that safely operates with puncture resistance to grasp and hold objects of various shapes and consistency. The study promises further development for zero‐power soft robots endowed with multiple deformation modes, sequential deployment, and tunable multistability.

Design, Modeling, and Application of Reinforced-Airbag-Based Pneumatic Actuators with High Load and Cellular Rearrangement.

Although various soft pneumatic actuators have been studied, their performance, including load capacity, has not been satisfied yet. Enhancing their actuation capability and using them to develop soft robots with high performance is still an open and challenging issue. In this study, we developed novel pneumatic actuators based on fiber-reinforced airbags as a solution to this problem, of which the maximum pressure reaches more than 100 kPa. Through cellular rearrangement, the developed actuators could bend uni- or bidirectionally, achieving large driving force, large deformation, and high conformability. Hence, they could be used to develop soft manipulators with relatively large payload (up to 10 kg, about 50 times the body self-weight) and soft climbing robots with high mobility. In this article, we first present the design of the airbag-based actuators and then model the airbag to obtain the relationship between the pneumatic pressure, external force, and deformation. Subsequently, we validate the models by comparing the simulated and measured results and test the load capacity of the bending actuators. Afterward, we present the development of a soft pneumatic robot that can rapidly climb horizontal, inclined, and vertical poles with different cross-sectional shapes and even outdoor natural objects, like bamboos, at a speed of 12.6 mm/s generally. In particular, it can dexterously transition between poles at any angle, which, to the best of our knowledge, has not been achieved before.

Inspired by Physical Intelligence of an Elephant Trunk: Biomimetic Soft Robot With Pre-Programmable Localized Stiffness

Soft robots exhibit promising dexterity and adaptability for manipulation because of their high compliance. However, the existing soft robots with invariant stiffness hardly interact with cluttered environments with varying curvatures. In this study, inspired by the maneuverability of an elephant trunk, we proposed a pneumatic soft robot comprised of soft pneumatic actuators and interference plates. By implementing interference plates in diverse patterns, the localized stiffness of our robot can be pre-programmed. To quantify the availability of localized stiffness regulation, we constructed four typical assembly fashions strengthened by the interference plates, and predicted robot profiles by simulation that was validated via experiments. We demonstrated the application of our soft robot with localized stiffness regulation in a variety of scenarios demanding specific configurations. Our design paradigm not only uncovers the potential methodology for regulating robotic curvature precisely, but may inspire next-generation soft robots integrating specified structural and material characteristics learned from natural intelligence.

Design of squeezing-tube-driven pump for soft pneumatic robotics based on spiral spring winding

Aiming at the demand for high-speed, easy-controllability, and integration of pneumatic soft robots and elastomer actuators, this study presents a squeezing-tube-driven pump (STDP) for soft pneumatic robotics based on spiral spring winding. This concept contains a customized spiral spring and a pneumatic tube with high-elasticity. The spiral spring is driven by an electric motor and coerced into winding deformation. Furthermore, the pneumatic tube is extruded by the spring and then the air in the tube is fast compressed to drive soft pneumatic grippers. The mechanical model and simulation are utilized to explain the operating principle of STDP. The air pressure and rotation angle of the spring under various rotation speeds are in a close linear correlation verified by the experimental results, which provides feasibility for easy controlling and rapid actuation. Finally, fast-gripping tests with an integrated gripper–pump system and a pneumatic muscle actuation test are presented to show the advantages of the proposed pump, respectively.

High‐Speed and Low‐Energy Actuation for Pneumatic Soft Robots with Internal Exhaust Air Recirculation

Multichamber soft pneumatic actuators (m‐SPAs) are widely used in soft robotic systems to achieve versatile grasping and locomotion. However, existing m‐SPAs have slow actuation speed and are either limited by a finite air supply or require energy‐consuming hardware to continuously supply compressed air. Herein, these shortcomings by introducing an internal exhaust air recirculation (IEAR) mechanism for high‐speed and low‐energy actuation of m‐SPAs are addressed. This mechanism recirculates the exhaust compressed air and recovers the energy by harnessing the rhythmic actuation of multiple chambers. A theoretical model to guide the analysis of the IEAR mechanism, which agrees well with the experimental results, is developed. Comparative experimental results of several sets of m‐SPAs show that the IEAR mechanism significantly improves the actuation speed by more than 82.4% and reduces the energy consumption per cycle by more than 47.7% under typical conditions. The promising applications of the IEAR mechanism in various pneumatic soft machines and robots such as a robotic fin, fabric‐based finger, and quadruped robot are further demonstrated. An interactive preprint version of the article can be found at: https://doi.org/10.22541/au.166428178.80668101/v1.

Movement Monitoring System for a Pneumatic Muscle Actuator

Recent advancements in soft pneumatic robot research have demonstrated these robots’ capability to interact with the environment and humans in various ways. Their ability to move over rough terrain and grasp objects of irregular shape, regardless of position, has garnered significant interest in developing new pneumatic soft robots. Integrating industrial design with related technologies holds great promise for the future, potentially bringing about a new lifestyle and revolutionizing the industry. As robots become increasingly practical, there is a growing need for sensitivity, robustness, and efficiency improvements. It is anticipated that the development of these intelligent pneumatic soft robots will play a critical role in serving the needs of society and production shortly. The present article is concerned with developing a system for monitoring a pneumatic robot’s parameters, including a spatial coordinate system. The focus is on utilizing the relationship between the coordinates and pressure to model the movement of the soft robot within the MATLAB simulation environment.

Cascade Control for Robust Tracking of Continuum Soft Robots With Finite-Time Convergence of Pneumatic System

Pneumatic soft robots have become the premier soft robot type among the plethora of soft robot testbeds under research, being the continuum pneumatic soft robot (cPSR) the most compliant, yet challenging due to its hyperelastic behavior of its constitutive elastomer material. In this type of cPSR, embedded pneumatic chambers materialize the pneumatic controller from within, thus, there arises two highly intertwined dynamical systems: the kinetic one due to the cPSR inertia and to the pneumatic system itself. Unfortunately, the embedded pneumatic control for the cPSR has been outlined using pneumatics developed for rigid bodies. In this letter, we study the resultant Lagrangian dynamics of the highly coupled nonlinear cPSR system equipped with 3 embedded pneumatic chambers (thus the system is fully actuated and controllable). Then, a robust feedback cascade tracking controller is proposed so that the cPSR control torque yields the desired pressure for the pneumatic dynamics. Chatterless integral sliding modes are proposed to render semi-global finite-time convergence of pressure tracking errors. Finally, simulations are presented, and concluding remarks are discussed.

Design and Feasibility Study of MRG-Based Variable Stiffness Soft Robot.

The conventional pneumatic soft robot has the problem of insufficient stiffness, while in the magnetorheological soft robot, the magnetic field provided by electromagnet has the disadvantage of oversized structure and poor flexibility. This paper presents a variable stiffness pneumatic soft robot based on magnetorheological grease (MRG) to solve these problems. Its three soft fingers cooperate with the adjustable gripper to adjust the gripping range for the robot hand, and it is used to provide gripping driving force through the bending drive. The MRG layer is designed on the gripping surface to provide adaptivity and rigid support for the gripped objects. A magnetic-air structure consisting of a Halbach array and Halbach array actuator is designed inside the soft fingers to provide a flexible magnetic field for the MRG layer. Theoretical and simulation analysis is carried out, and the results show that the state of the MRG changes and the stiffness of the clamping surface changes under the working pressure of 30 kPa. Finally, the experiment further proves the variable and high adaptivity of the surface stiffness of the gripping surface to reduce the damage to the gripped objects.

A Bionic pipe-crawling soft robot based on the pneumatic silicone actuator

To realize the real-time monitoring of pipelines, this paper designs a pneumatic soft pipeline outer wall-crawling robot composed of OMCA (outer multi-cavity actuator) based on the motion of the inchworm. The robot consists of a torso and two pneumatic grippers. It is controlled by three air pumps and can realize pipeline linear motion. Use ABAQUS to perform finite element analysis on OMCA and measure its key geometric parameters under different pressure levels, and then test the robot’s kinematic performance. The movement speed of the robot on a pipe with a diameter of 10 cm is 0.3 mm/s.

Buckling of Thin-Walled Cylinders from Three Dimensional Nonlinear Elasticity.

The famous bifurcation analysis performed by Flügge on compressed thin-walled cylinders is based on a series of simplifying assumptions, which allow to obtain the bifurcation landscape, together with explicit expressions for limit behaviours: surface instability, wrinkling, and Euler rod buckling. The most severe assumption introduced by Flügge is the use of an incremental constitutive equation, which does not follow from any nonlinear hyperelastic constitutive law. This is a strong limitation for the applicability of the theory, which becomes questionable when is utilized for a material characterized by a different constitutive equation, such as for instance a Mooney-Rivlin material. We re-derive the entire Flügge's formulation, thus obtaining a framework where any constitutive equation fits. The use of two different nonlinear hyperelastic constitutive equations, referred to compressible materials, leads to incremental equations, which reduce to those derived by Flügge under suitable simplifications. His results are confirmed, together with all the limit equations, now rigorously obtained, and his theory is extended. This extension of the theory of buckling of thin shells allows for computationally efficient determination of bifurcation landscapes for nonlinear constitutive laws, which may for instance be used to model biomechanics of arteries, or soft pneumatic robot arms.

Stiffness Adaptation of a Hybrid Soft Surgical Robot for Improved Safety in Interventional Surgery.

Minimally invasive instruments are inserted per-cutaneously and are steered toward the desired anatomy. The low stiffness of instruments is an advantage; however, once the target is reached, the instrument usually is required to transmit force to the environment. The main limitation of the constant stiffness is predetermined maneuverability and cap of force transmission. Whereas, a highly flexible device can be safely steered through the body but is not suitable for payload limit, while a highly stiff device can have relatively high loads but cannot be steered in highly tortuous trajectories. To overcome this limitation, an adaptive stiffness soft robot was proposed, and the effects of the chamber pressure on the stiffness of the soft robot were investigated. To this end, a single-chamber pneumatic soft robot with one tendon was designed and fabricated. Afterward, a continuum mechanics model based on the nonlinear Cosserat rod model with hyperelastic material model and large deformation kinematics of the robot was developed. The shooting method solved the model as a boundary value problem with Dirichlet and Neumann boundary conditions. The results of the model showed stiffness adaptation feasibility with simultaneous tendon-driving and pneumatic actuation. Thus, to validate the theoretical findings, a series of experimental studies were performed with pressure in the range of 33 to 44 kPa and tendon tensions in the range of 0 to 2.7 N. The theoretical and experimental results for tip displacement and stiffness showed similar trends with a maximum error of 8.25%.

Toward the Development of Large-Scale Inflatable Robotic Arms Using Hot Air Welding.

The manufacturing method of soft pneumatic robots affects their ability to maintain their impermeability when pressurized. Pressurizing them beyond their limits results in leaks or ruptures of the structure. Increasing their size simultaneously increases the tension forces within their structure and reduces their ability to withstand the pressures necessary for them to operate. This article introduces the use of hot air welding to manufacture three-dimensional inflatable elements containing only lap seals which can sustain larger tension forces than the fin seals used in most other inflatable robotic arms. This manufacturing technique is then used to form inflatable joints with 2-degrees of freedom (DOFs), which can be assembled to form 6-DOFs robotic arms. A dual-arm inflatable robot was built using two arms each with a length of 85 cm, was capable of lifting payloads up to 3 kg, had a large range of motion, and was able to lift misaligned boxes using its two arms relying only on friction force by pushing on both sides of the box. The arm concept was then scaled to form a robotic arm with a length of nearly 5 m, which was able to pickup and place a basketball in a basketball hoop from the free-throw line several meters away. The present work advances the state of the art in building large-scale soft robotic arms.

Freeform Fabrication of Pneumatic Soft Robots via Multi‐Material Jointed Direct Ink Writing

Front Cover: In article number 2100813 by Weicheng Cui, Nanjia Zhou, and co-workers, a multi-material jointed direct ink writing method is proposed to fabricate various actuators and robots employing materials featuring distinct mechanical properties. The printed manipulator has great motion performance and is capable of completing delicate tasks, e.g., pipeline operation. The proposed method is easily extendable to other soft robots with various functional materials with different electrical, optical, and mechanical properties for applications including biomimetic sensing, camouflage, and many others.

Pneumatic Soft Robots: Challenges and Benefits

In the field of robotics, soft robots have been showing great potential in the areas of medical care, education, service, rescue, exploration, detection, and wearable devices due to their inherently high flexibility, good compliance, excellent adaptability, and natural and safe interactivity. Pneumatic soft robots occupy an essential position among soft robots because of their features such as lightweight, high efficiency, non-pollution, and environmental adaptability. Thanks to its mentioned benefits, increasing research interests have been attracted to the development of novel types of pneumatic soft robots in the last decades. This article aims to investigate the solutions to develop and research the pneumatic soft robot. This paper reviews the status and the main progress of the recent research on pneumatic soft robots. Furthermore, a discussion about the challenges and benefits of the recent advancement of the pneumatic soft robot is provided.

A Chemical Pump that Generates High‐Pressure Gas by Transmitting Liquid Fuel against Pressure Gradient

A pneumatic soft robot can be made autonomous by carrying a liquid chemical fuel. In the existing design, to transmit the fuel, the pressure of the fuel tank must exceed that of the actuator. Consequently, the fuel tank must be sufficiently stiff, which hardens the robot. Herein, inspired by pit membranes in trees, a chemical pump is developed, which is consisting of a nanoporous membrane between the fuel tank and the actuator, and coated with a catalyst on the side of the actuator. The fuel in the fuel tank migrates across the membrane and, on meeting the catalyst, decomposes into a pressurized gas and inflates the actuator. The chemical pump is driven by the free energy of reaction, against the difference in pressure. The pores in the membrane are large enough for the fuel molecules to migrate through, but small enough to block the pressurized gas to tunnel back. In a demonstration, the fuel tank has ambient pressure, and the actuator has a pressure of 350 kPa, comparable to the pressure in a car tire. The chemical pump enables pneumatic robots to be autonomous, powerful, and soft.

Freeform Fabrication of Pneumatic Soft Robots via Multi‐Material Jointed Direct Ink Writing

AbstractPneumatically actuated soft robots have attracted significant attention in recent years due to their non‐linear structures for performing biomimetic motions to enhance human‐machine interactions. However, manufacturing soft robots, especially those featuring complex 3D structures, still faces significant challenges as traditional lithography‐based micro/nanofabrication technologies have some limitations, such as limited material choices and layer‐by‐layer architectures. In this work, a facile multi‐material jointed direct ink writing (MJDIW) printing method is introduced. In comparing with the traditional micro/nanofabrication and other additive manufacturing methods, the method enables truly freeform 3D printing to fabricate entirely soft actuators and robots with complex 3D structures, while integrating materials with different mechanical characteristics to expand the manufacturing capabilities of additive manufacturing methods. The material properties and printing parameters, and conducted finite element analysis (FEA) is systematically investigated to provide the general design guidelines through simulating actuator motions. Several actuators such as linear elongation and bending actuators are manufactured either by employing a single material or multiple materials with different mechanical properties. Finally, a multi‐directional soft manipulator with complex internal channels is printed using different materials to illustrate the versatility of the printing methods.

Design and Characterization of a 3D-Printed Pneumatically-Driven Bistable Valve With Tunable Characteristics

Although research studies in pneumatic soft robots develop rapidly, most pneumatic actuators are still controlled by rigid valves and conventional electronics. The existence of these rigid, electronic components sacrifices the compliance and adaptability of soft robots.} Current electronics-free valve designs based on soft materials are facing challenges in behaviour consistency, design flexibility, and fabrication complexity. Taking advantages of soft material 3D printing, this paper presents a new design of a bi-stable pneumatic valve, which utilises two soft, pneumatically-driven, and symmetrically-oriented conical shells with structural bistability to stabilise and regulate the airflow. The critical pressure required to operate the valve can be adjusted by changing the design features of the soft bi-stable structure. Multi-material printing simplifies the valve fabrication, enhances the flexibility in design feature optimisations, and improves the system repeatability. In this work, both a theoretical model and physical experiments are introduced to examine the relationships between the critical operating pressure and the key design features. Results with valve characteristic tuning via material stiffness changing show better effectiveness compared to the change of geometry design features (demonstrated largest tunable critical pressure range from 15.3 to 65.2 kPa and fastest response time $\leq$ 1.8 s.

Pneumatic System Capable of Supplying Programmable Pressure States for Soft Robots

Pneumatic soft robots are of great interest in varieties of potential applications due to their unique capabilities compared with rigid structures. As a part of the soft robotic system, the pneumatic system plays a very important role as all motion performance is ultimately related to the pressure control in air chambers. With the increasing flexibility and complexity of robotic tasks, diverse pneumatic robots driven by positive, negative, or even hybrid pressure are developed, and this comes with higher requirements of pneumatic system and air pressure control precision. In this study, we aim to propose a simplified pneumatic design capable of generating programmable pressure states ranging from negative to positive pressure in each air branch. Based on the design concept and system configuration, special inflation and deflation strategies and closed-loop feedback control strategy are proposed to achieve precise pressure control. Then, a prototype of the pneumatic system with six independent air supply branches is designed and fabricated. Experimental results show that the pneumatic system can achieve a wide range of pressure from -59 to 112 kPa. The speed of inflation and deflation is controllable. Finally, we demonstrate three robotic applications and design the related algorithms to verify the feasibility and practicability of the pneumatic system. Our proposed pneumatic design can satisfy the pressure control requirements of a variety of soft robots driven by both positive and negative pressure. It can be used as a universal pneumatic platform, which is inspiring for actuation and control in the soft robotic field.