Fiber-Reinforced Origamic Robotic Actuator

Pneumatic artificial muscles (PAMs) are soft actuators that generate tension via contraction when supplied with compressed air. Although PAMs have been widely used in robots mimicking endoskeletal organisms, recent advancements in millimeter-scale thin PAMs have enabled a more precise replication of complex musculoskeletal systems. In contrast, exoskeletal organisms, such as crustaceans and insects actuate their joints using pennate muscles embedded within their exoskeletons. However, integrating actuators into the exoskeletons of exoskeletal-inspired robots is challenging owing to spatial constraints. Consequently, wire and servo-driven mechanisms are predominantly employed, and studies on exoskeletal robots incorporating the muscle-apodeme structures of exoskeletal organisms remain largely unexplored. To address this gap, this paper presents the development of a crab-inspired robotic walking leg featuring an exoskeletal structure with embedded pneumatic artificial pennate muscles, modeled after the muscle-apodeme structures of snow crabs. The experimental evaluations demonstrated that the robot successfully performed joint opening and closing motions, achieving a range of motion comparable to that of a snow crab.

Pneumatic actuators are fast becoming a key instrument where cost, safety or pollution is a concern. They can be of linear or rotary type, depending on the motion they produce. Linear pneumatic actuator is also commonly known as pneumatic cylinder because it usually consists of a piston housed in a hollow cylinder. In this study, the feasibility of PID control for a double-acting cylinder actuated by McKibben muscles (DACAM) had been investigated. Due to the nonlinearity and hysteresis properties of the muscle, separate controllers for forward actuation and reverse actuation had been used. Result shows that when given a staircase input, the feedback system gave an average response of 4.28 s rise time, 6.06 s settling time, 0.01% overshoot and 0.01% steady-state error for forward actuation and 8.25 s fall time, 9.28 s settling time, 2.86% overshoot and 2.86% steady-state error for reverse actuation. The evidence from this study suggests that position control of a DACAM using PI control is possible. An implication of this is the possibility of developing a small, lightweight and simple pneumatic cylinder using McKibben muscles.

Soft pneumatic actuators are used to steer soft growing "vine" robots while being flexible enough to undergo the tip eversion required for growth. In this study, we compared the performance of three types of pneumatic actuators in terms of their ability to perform eversion, quasi-static bending, dynamic motion, and force output: the pouch motor, the cylindrical pneumatic artificial muscle (cPAM), and the fabric pneumatic artificial muscle (fPAM). The pouch motor is advantageous for prototyping owing to its simple manufacturing process. The cPAM exhibits superior bending behavior and produces the highest forces, whereas the fPAM actuates fastest and everts at the lowest pressure. We evaluated a range of dimensions for each actuator type. Larger actuators can produce more significant deformations and forces, but smaller actuators inflate faster and can evert at a lower pressure. Because vine robots are lightweight, the effect of gravity on the functionality of different actuators is minimal. We developed a new analytical model that predicts the pressure-to-bending behavior of vine robot actuators. Using the actuator results, we designed and demonstrated a 4.8 m long vine robot equipped with highly maneuverable 60 × 60 mm cPAMs in a three-dimensional obstacle course. The vine robot was able to move around sharp turns, travel through a passage smaller than its diameter, and lift itself against gravity.

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

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

The field of Soft Robotics proposes the use of flexible and compliant materials in the fabrication of soft actuators that can interact with humans in a safer way than conventional robots. While soft pneumatic actuators operate with positive pressure inflating their chambers and creating movement, vacuum actuators operate with negative pressure collapsing their chambers to generate movement. The latter have the benefit that they do not burst due to excessive pressure during contraction and since they shrink in size when activated, they can fit into tight spaces and are therefore more compact, aside from possibly being able to expand with positive pressure. This work presents a soft pneumatic linear actuator designed as a bellow-shaped structure made of silicone rubber that operates with negative pressure to contract and with positive pressure to extend. A Finite Element Method dynamic analysis was performed, using the SIMULIA Abaqus software, to predict the actuator’s behavior. From the definition of the geometry, molds composed of modular pieces were designed and 3D printed to fabricate the actuator prototype. A test platform was designed to perform tests to characterize the actuator and then implement a position and pressure cascade control system, designed with a fuzzy pressure controller in the inner loop and a PI position controller in the outer loop, to regulate both the contraction and the extension of the actuator.

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

This paper presents a layering approach for the manufacturing of pneumatic soft actuators as a coalesced solution to the diverse array of existing fabrication methods. While most research groups have developed their own (often tedious) fabrication strategies for soft actuators, these methods are usually based on available equipment and project-specific design requirements, making them impractical for use in other laboratories. In contrast, the layered substrate approach enables repeatable production of highly-capable pneumatic actuators that can be easily customized to suit a variety of applications. Here we propose layering fiber-reinforced silicone on both sides of a thin pneumatic chamber to directionally constrain expansion. Similar in concept to the Venus flytrap, pressurization of the chamber causes the module to deform and expand where unrestrained. Strategic orientation and patterning of the fiber reinforcement layers results in multiple unique shear and bending capabilities upon pressurization. Combinations of multiple reinforced pneumatic units in series or parallel could match the capabilities of most soft pneumatic actuators, while requiring only simple, universal fabrication methods that may be replicated by other research groups.

Soft pneumatic actuator with an embedded flexible polymeric piezoelectric membrane for sensing bending deformation

Benefit from high compliance, lightweight and natural motion, soft pneumatic actuators (SPAs) have shown great potential for using as fingers in robotic hands. Currently designed SPAs lack strain feedback, which limits their further applications. Soft fingers using SPAs require sensors embedded in their bodies for strain feedback, and most of the reported sensors used in SPAs are commercial products which suffer from low compliance, bulky volume and integration complexity. This work reports a SPA finger with self-strain sensing by integrating a SPA and a dielectric elastomer (DE) film capacitive strain sensor. The single-chamber with fiber reinforced SPA is chosen for bending motion. The DE film capacitive strain sensor is designed with a simple sandwiched structure which is easy-to-fabricate and thick enough for high compliance. The materials chosen to fabricate the SPA and the sensor are the same which helps to make the integration natural and closely bonded. The actuation response as well as sensing outputs are experimentally analyzed and results show that the sensing output change linearly with bending angles, which can be used for further position feedback control.

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

Among various soft actuators, soft pneumatic actuators (SPAs) powered by pressurized gases have been widely adopted due to their structural simplicity, ease of fabrication, and ability to generate diverse and adaptable motions. However, conventional mechanical compressors and chemical reaction-based pneumatic sources that supply pressurized gas to these actuators often generate substantial acoustic noise and heat, limiting their practical use. In this study, we propose an electronics-free, near-silent, and low-heat pneumatic source that integrates endothermic-exothermic chemical reactions to balance heat generation while producing pressurized gas. By only using passive mechanical components that autonomously regulate the reaction process, the pneumatic source achieved a steady output pressure of 7 bar and a flow rate of 6 liters per minute through the chemical reactions between phosphoric acid and cesium bicarbonate. The proposed pneumatic source operated with minimal temperature rise (maximum 36°C) and low acoustic noise of 40 dBA, comparable to the ambient noise of a quiet residential environment. The proposed approach demonstrates an enthalpy-balanced acid-bicarbonate system for combining endothermic and exothermic reactions to achieve thermally balanced and noise-suppressed pneumatic operation. Therefore, the proposed concept can serve as a practical and versatile pneumatic source for driving a wide range of SPAs.

Soft pneumatic actuators (SPAs), as novel types of motion drivers for robotic devices, excel in many applications, such as rehabilitation and biomimicry, which demand compliance and softness. To further expand their scope of utilization, the SPAs should be customizable to meet the distinctive requirements of different applications. This article proposes a novel perspective on the SPA working mechanism based on stiffness distribution and then presents a versatile method called stiffness customization and patterning (SCP) for SPA body stiffness layout as a novel attempt to customize SPAs with distinctive properties. We fabricated a hybrid type of material combining unstretchable material and silicone with customizable aggregated elasticity. The tensile results showed that embedding unstretchable material directly increases the stiffness of the hybrid material sample, and our stress-strain model for SCP is able to adequately predict the elasticity of hybrid samples with specific material ratios. By applying this approach to bending-type SPAs, we are able to mitigate SPA buckling, a main failure mode of SPAs, and improve the SPA tip force by using hybrid material with globally increased stiffness. We also diversify bending modalities with different stiffness configurations in the hybrid material. SCP offers numerous ways to engineer SPAs for more applications.

In this study, in order to realize an assist of independent life for the elderly or people in need of care and relieve a physical burden for care worker, an active support splint driven by pneumatic soft actuator (ASSIST) has been developed. ASSIST consists of a plastic interface with the palm and arm and two rotary-type soft actuators put in both sides of appliance. McKibben type pneumatic rubber muscles are on the both sides of rotary-type soft actuators for relieving a restrained feeling when the device is not operated. In this paper, the structure of ASSIST is described, and then the effectiveness of this splint is experimentally discussed based on the experiments for movable range assist for the wrist.

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