Pneumatic Soft Robots Research Articles

Fluidic feedback for soft actuators: an electronic-free system for sensing and control

The field of pneumatic soft robotics is on the rise. However, most pneumatic soft robots still heavily rely on rigid valves and conventional electronics for control, which detracts from their natural flexibility and adaptability. Efforts have focused on substituting electronic controllers with pneumatic counterparts to address this limitation. Despite significant progress, contemporary soft control systems still face considerable challenges, as they predominantly depend on pre-programmed commands instead of real-time sensory feedback. To confront these challenges, we propose an electronic-free soft actuator system capable of achieving basic sensorimotor behaviors. The soft actuator employs a fluidic strain sensor to obtain proprioception, detecting changes in air impedance resulting from stretching and compression. Integration of this sensor with a pneumatic valve enables the soft actuator possessing basic sensing and control capabilities. Drawing inspiration from the somatosensory and neuromuscular systems found in biological organisms, we implement both open-loop and closed-loop motion modes using different connection configurations. They facilitate cyclic movement and sensory feedback-regulated motion control using 'material intelligence'. We envisage that this system has the potential to expand to accommodate multiple limbs, thereby pioneering the development of fully fluidic soft robots.

Design and gait research of pneumatic soft quadruped robot

Soft robots possess flexibility and, in theory, an unlimited number of degrees of freedom. These characteristics give them superior flexibility, making them better suited for navigating complex terrain, such as steep or rugged environments, compared to rigid robots. The design of the quadruped robot is based on the deformation principles of a pneumatically driven honeycomb network, with leg deformation controlled through air pressure regulation. Furthermore, the mathematical model of the quadruped robot is developed, including both a vertical elongation model and a bending elongation model of the leg structure, established through geometric analysis. An experimental platform for the quadruped robot system is then constructed, and experimental analyses are performed to assess the elastic coefficient, hysteresis performance, elongation capacity, and bending performance of one of the robot’s legs, verifying the accuracy of the mathematical model. Based on control requirements, LabVIEW is used to design static and dynamic gait programs for the quadruped robot, ultimately enabling control of its walking motion.

Physics-Guided Deep Learning Enabled Surrogate Modeling for Pneumatic Soft Robots

Physics-Guided Deep Learning Enabled Surrogate Modeling for Pneumatic Soft Robots

Modular Stimuli‐Responsive Valves for Pneumatic Soft Robots

Pneumatic soft robots have several advantages, including facile fabrication, versatile deformation modes, and safe human–machine interaction. However, pneumatic soft robots typically rely on mechatronics to interact with their environment, which can limit their form factors and reliability. Researchers have considered how to achieve autonomous behaviors using the principles of mechanical computing and physical intelligence. Herein, modular responsive valves that can autonomously regulate airflow within pneumatic soft robots in response to various environmental stimuli, including light, water, and mechanical forces, are described. By combining multiple types of valves, autonomous logic gates and more advanced logical operations can be realized. Finally, it is demonstrated that responsive valves can be integrated with pneumatic soft robots, allowing autonomous morphing and navigation. This framework provides a strategy for creating autonomous pneumatic robots that can respond to multiple stimuli in their environment.

Soft Phononic Crystal with Tunable Bandgap Through Pneumatic Actuation

Pneumatic manipulation has the advantages of low cost, lightweight design, fast response, and ease of integration. However, its application in the field of phononic crystals remains limited. Inspired by pneumatic soft robots, this article proposes a pneumatic soft phononic crystal arranged in a square lattice, incorporating four pneumatic actuators within the scatterer. By manipulating air pressure, the bandgap can be effectively opened and closed. The finite element analysis is employed to examine the deformation and bandgaps of the pneumatic soft phononic crystal under varying air pressures. Moreover, the effect of the scatterer's rotation angle on the bandgap evolution in the phononic crystal is parametrically investigated. The results show that varying both the volume and the rotation angle of the scatterer can achieve bandgap opening, closing, and tuning. The proposed phononic crystal presents obvious practical applications and provides important insights for the design of soft‐tunable acoustic devices.

Spring-reinforced pneumatic actuator and soft robotic applications

Abstract Compared to rigid-structure robots, soft robots possess higher degrees of freedom and stronger environmental adaptability, which has aroused increasing attention in the robotic field. Among them, soft pneumatic robots have excellent performances in various practical applications. However, the nonlinearity and instability of pressure response of soft actuators caused by lateral expansion come to a great challenge. To address this problem, we proposed to embed a spring constraint layer around each single air chamber. Following the design concept, we obtained single-cavity and multi-DoF pneumatic actuators and evaluated their elongation and bending characteristics. Experimental results demonstrated that our proposed actuators have more linear pressure response as well as higher consistency. Eventually, through robotic applications, including soft robotic hand and gripper our proposed actuators could facilitate flexible manipulation and elaborate performance.

An electropermanent magnet valve for the onboard control of multi-degree of freedom pneumatic soft robots

To achieve coordinated functions, fluidic soft robots typically rely on multiple input lines for the independent inflation and deflation of each actuator. Fluidic actuators are controlled by rigid electronic pneumatic valves, restricting the mobility and compliance of the soft robot. Recent developments in soft valve designs have shown the potential to achieve a more integrated robotic system, but are limited by high energy consumption and slow response time. In this work, we present an electropermanent magnet (EPM) valve for electronic control of pneumatic soft actuators that is activated through microsecond electronic pulses. The valve incorporates a thin channel made from thermoplastic films. The proposed valve (3 × 3 × 0.8 cm, 2.9 g) can block pressure up to 146 kPa and negative pressures up to –100 kPa with a response time of less than 1 s. Using the EPM valves, we demonstrate the ability to switch between multiple operation sequences in real time through the control of a six-DoF robot capable of grasping and hopping with a single pressure input. Our proposed onboard control strategy simplifies the operation of multi-pressure systems, enabling the development of dynamically programmable soft fluid-driven robots that are versatile in responding to different tasks.

Multimodal soft valve enables physical responsiveness for preemptive resilience of soft robots.

Resilience is crucial for the self-preservation of biological systems: Humans recover from wounds thanks to an immune system that autonomously enacts a multistage response to promote healing. Similar passive mechanisms can enable pneumatic soft robots to overcome common faults such as bursts originating from punctures or overpressurization. Recent technological advancements, ranging from fault-tolerant controllers for robot reconfigurability to self-healing materials, have paved the way for robot resilience. However, these techniques require powerful processors and large datasets or external hardware. How to extend the operational life span of damaged soft robots with minimal computational and physical resources remains unclear. In this study, we demonstrated a multimodal pneumatic soft valve capable of passive resilient reactions, triggered by faults, to prevent or isolate damage in soft robots. In its forward operation mode, the valve, requiring a single supply pressure, isolated punctured soft inflatable elements from the rest of the soft robot in as fast as 21 milliseconds. In its reverse operation mode, the valve can passively protect robots against overpressurization caused by external disturbances, avoiding plastic deformations and bursts. Furthermore, the two modes combined enabled the creation of an endogenously controlled valve capable of autonomous burst isolation. We demonstrated the passive and quick response and the possibility of monolithic integration of the soft valve in grippers and crawling robots. The approach proposed in this study provides a distributed small-footprint alternative to controller-based resilience and is expected to help soft robots achieve uninterrupted long-lasting operation.

Programmable Pressure Control in Pneumatic Soft Robots With 2-Way 2-State Solenoid Valves

Programmable Pressure Control in Pneumatic Soft Robots With 2-Way 2-State Solenoid Valves

Multi-modal Bionic Motion Analysis of A Cpg-controlled Pneumatic Soft Robot

Multi-modal Bionic Motion Analysis of A Cpg-controlled Pneumatic Soft Robot

Research and Implementation of Pneumatic Amphibious Soft Bionic Robot

To meet the requirements of amphibious exploration, ocean exploration, and military reconnaissance tasks, a pneumatic amphibious soft bionic robot was developed by taking advantage of the structural characteristics, motion forms, and propulsion mechanisms of the sea lion fore-flippers, inchworms, Carangidae tails, and dolphin tails. Using silicone rubber as the main material of the robot, combined with the driving mechanism of the pneumatic soft bionic actuator, and based on the theory of mechanism design, a systematic structural design of the pneumatic amphibious soft bionic robot was carried out from the aspects of flippers, tail, head–neck, and trunk. Then, a numerical simulation algorithm was used to analyze the main executing mechanisms and their coordinated motion performance of the soft bionic robot and to verify the rationality and feasibility of the robot structure design and motion forms. With the use of rapid prototyping technology to complete the construction of the robot prototype body, based on the motion amplitude, frequency, and phase of the bionic prototype, the main execution mechanisms of the robot were controlled through a pneumatic system to carry out experimental testing. The results show that the performance of the robot is consistent with the original design and numerical simulation predictions, and it can achieve certain maneuverability, flexibility, and environmental adaptability. The significance of this work is the development of a pneumatic soft bionic robot suitable for amphibious environments, which provides a new idea for the bionic design and application of pneumatic soft robots.

Design, performance analysis and applications of pneumatic bellows actuator for building block soft robots

Currently, there are some new challenges for pneumatic soft robots brought by complex application environments and variable task objectives. To address these challenges, inspired by the building blocks, we develop a novel pneumatic soft actuator named pneumatic bellows actuator (PBA) that can generate bidirectional deformation, and propose a building block design concept for the soft robots based on the developed PBA. The PBA consists of three parts: a soft rubber layer (SRL), a fiber-reinforced layer (FRL) and some rigid joints. We design the SRL as a bellows-like shape so the PBA can generate bidirectional deformation, and weave an FRL as the coating of the SRL to prevent the significant radial expansion of the SRL that may affect the application of the PBA. The rigid joints include sealing glands and connectors. The sealing glands are used to seal the SRL, while the connectors having interfaces on their five surfaces are used to connect the PBAs through the customized plugs corresponding to these interfaces. Moreover, the experimental results indicate that the PBA can generate large deformation and driving force, while it has the advantages of good repeatability and approximate rate-independent under low frequency. Based on the building block design concept for the soft robots, we construct three PBA-based soft robots: a soft crawling robot, a soft gripper, and a soft manipulator, to demonstrate that we can easily use the PBAs to construct various soft robots.

Discrete-Time Impedance Control for Dynamic Response Regulation of Parallel Soft Robots.

Accurately controlling the dynamic response and suppression of undesirable dynamics such as overshoots and vibrations is a vital requirement for soft robots operating in industrial environments. Pneumatically actuated soft robots usually undergo large overshoots and significant vibrations when deactuated because of their highly flexible bodies. These large vibrations not only decrease the reliability and accuracy of the soft robot but also introduce undesirable characteristics in the system. For example, it increases the settling time and damages the body of the soft robot, compromising its structural integrity. The dynamic behavior of the soft robots on deactuation needs to be accurately controlled to increase their utility in real-world applications. The literature on pneumatic soft robots still does not sufficiently address the issue of suppressing undesirable vibrations. To address this issue, we propose the use of impedance control to regulate the dynamic response of pneumatic soft robots since the superiority of impedance control is already established for rigid robots. The soft robots are highly nonlinear systems; therefore, we formulated a nonlinear discrete sliding mode impedance controller to control the pneumatic soft robots. The formulation of the controller in discrete-time allows efficient implementation for a high-order system model without the need for state-observers. The simplification and efficiency of the proposed controller enable fast implementation of an embedded system. Unlike other works on pneumatic soft robots, the proposed controller does not require manual tuning of the controller parameters and automatically calculates the parameters based on the impedance value. To demonstrate the efficacy of the proposed controller, we used a 6-chambered parallel soft robot as an experimental platform. We presented the comparative results with an existing state-of-the-art controller in SMC control of pneumatic soft robots. The experiment results indicate that the proposed controller can effectively limit the amplitude of the undesirable vibrations.

A Soft Collaborative Robot for Contact-based Intuitive Human Drag Teaching.

Soft material-based robots, known for their safety and compliance, are expected to play an irreplaceable role in human-robot collaboration. However, this expectation is far from real industrial applications due to their complex programmability and poor motion precision, brought by the super elasticity and large hysteresis of soft materials. Here, a soft collaborative robot (Soft Co-bot) with intuitive and easy programming by contact-based drag teaching, and also with exceptional motion repeatability (< 0.30% of body length) and ultra-low hysteresis (< 2.0%) is reported. Such an unprecedented capability is achieved by a biomimetic antagonistic design within a pneumatic soft robot, in which cables are threaded to servo motors through tension sensors to form a self-sensing system, thus providing both precise actuation and dragging-aware collaboration. Hence, the Soft Co-bots can be first taught by human drag and then precisely repeat various tasks on their own, such as electronics assembling, machine tool installation, etc. The proposed Soft Co-bots exhibit a high potential for safe and intuitive human-robot collaboration in unstructured environments, promoting the immediate practical application of soft robots.

Toward Onboard Proportional Control of Multi-Chamber Soft Pneumatic Robots: A Magnetorheological Elastomer Valve Array.

Soft pneumatic actuators (SPAs) are commonly used in various applications because of their structural compliance, low cost, ease of manufacture, high adaptability, and safe human-robot interaction. The traditional approach for achieving proportional control of soft pneumatic robots requires the use of industrial proportional valves or syringe drivers, which are not only rigid and bulky but also hard to be integrated into the body of soft robots. In our previous research, we developed a Magnetorheological elastomer (MRE)-based soft valve that showed advantages for controlling SPAs due to its compliance, compactness, robustness, and compatibility for continuous pressure modulation. Modern soft robots with multiple chambers require more MRE valves onboard for their control. However, merely packing more MRE valves for soft robots can cause problems like magnetic interference, flow rate deviation, and overheating. Therefore, in this study, we proposed a two-dimensional MRE valve array design to solve issues of magnetic interference and overheating when expanding from a single MRE proportional valve into an integrated array. The magnetic interference and the overheating problem were investigated through multiphysics simulation, bringing the optimal choice of valve spacing (1.2 times the single valve diameter), magnetic coil pole arrangement (same pole), and the cooling system design (internal cooling chamber with flowing water). Physical experiments showed that our MRE valve array maintained its original flowrate performance with low magnetic interference (0.89 mT) and low coil temperature (under 73.9°C for 5 min).

Parametric study of soft pneumatic robot grippers through finite element analysis

This paper investigates the gripping stress and deformation of pneumatically-actuated fluidic elastomer actuation (FEA)-based soft robotic gripper through ansys finite element analysis software. By varying gripper parameters, i.e. Input pressures and clearance to the object, simulations on the deformation of the soft fingers are performed to achieve gripping of the object. The motivation of this parametric study is to facilitate the design optimization of soft robotic grippers. Results demonstrate that grippers with lesser clearance to the object require lesser input pressure to achieve similar gripping stress on the object although it is evident that grippers with higher clearance are able to cater for wider range of object sizes.

Design, Manufacturing, and Open-Loop Control of a Soft Pneumatic Arm

Soft robots distinguish themselves from traditional robots by embracing flexible kinematics. Because of their recent emergence, there exist numerous uncharted territories, including novel actuators, manufacturing processes, and advanced control methods. This research is centred on the design, fabrication, and control of a pneumatic soft robot. The principal objective is to develop a modular soft robot featuring multiple segments, each one with three degrees of freedom. This yields a tubular structure with five independent degrees of freedom, enabling motion across three spatial dimensions. Physical construction leverages tin-cured silicone and a wax-casting method, refined through an iterative processes. PLA moulds that are 3D-printed and filled with silicone yield the desired model, while bladder-like structures are formed within using solidified paraffin wax-positive moulds. For control, an empirically fine-tuned open-loop system is adopted. This paper culminates in rigorous testing. Finally, the bending ability, weight-carrying capacity, and possible applications are discussed.

Research on control strategy of pneumatic soft bionic robot based on improved CPG.

To achieve the accuracy and anti-interference of the motion control of the soft robot more effectively, the motion control strategy of the pneumatic soft bionic robot based on the improved Central Pattern Generator (CPG) is proposed. According to the structure and motion characteristics of the robot, a two-layer neural network topology model for the robot is constructed by coupling 22 Hopfield neuron nonlinear oscillators. Then, based on the Adaptive Neuro-Fuzzy Inference System (ANFIS), the membership functions are offline learned and trained to construct the CPG-ANFIS-PID motion control strategy for the robot. Through simulation research on the impact of CPG-ANFIS-PID input parameters on the swimming performance of the robot, it is verified that the control strategy can quickly respond to input parameter changes between different swimming modes, and stably output smooth and continuous dynamic position signals, which has certain advantages. Then, the motion performance of the robot prototype is analyzed experimentally and compared with the simulation results. The results show that the CPG-ANFIS-PID motion control strategy can output coupled waveform signals stably, and control the executing mechanisms of the pneumatic soft bionic robot to achieve biological rhythms motion propulsion waveforms, confirming that the control strategy has accuracy and anti-interference characteristics, and enable the robot have certain maneuverability, flexibility, and environmental adaptability. The significance of this work lies in establishing a CPG-ANFIS-PID control strategy applicable to pneumatic soft bionic robot and proposing a rhythmic motion control method applicable to pneumatic soft bionic robot.

Modeling and Design of Lattice-Reinforced Pneumatic Soft Robots

Modeling and Design of Lattice-Reinforced Pneumatic Soft Robots

Integrated Design and Fabrication of Pneumatic Soft Robot Actuators in a Single Casting Step.

Bio-inspired soft robots have already shown the ability to handle uncertainty and adapt to unstructured environments. However, their availability is partially restricted by time-consuming, costly, and highly supervised design-fabrication processes, often based on resource-intensive iterative workflows. Here, we propose an integrated approach targeting the design and fabrication of pneumatic soft actuators in a single casting step. Molds and sacrificial water-soluble hollow cores are printed using fused filament fabrication. A heated water circuit accelerates the dissolution of the core's material and guarantees its complete removal from the actuator walls, while the actuator's mechanical operability is defined through finite element analysis. This enables the fabrication of actuators with non-uniform cross-sections under minimal supervision, thereby reducing the number of iterations necessary during the design and fabrication processes. Three actuators capable of bending and linear motion were designed, fabricated, integrated, and demonstrated as 3 different bio-inspired soft robots, an earthworm-inspired robot, a 4-legged robot, and a robotic gripper. We demonstrate the availability, versatility, and effectiveness of the proposed methods, contributing to accelerating the design and fabrication of soft robots. This study represents a step toward increasing the accessibility of soft robots to people at a lower cost.