Soft actuators are gaining increasing popularity in various fields, including marine engineering and biomedical engineering. However, due to their nonlinear properties and significant material deformation, dynamic modeling of soft actuators for motion behavior is quite a challenge, especially for underwater environments. This article ingeniously combines Euler–Bernoulli theory and Cosserat rod theory to propose an efficient and accurate dynamic model for solving the underwater motion behavior of fiber-reinforced soft actuators. Under the assumption of neglecting external forces, we first utilize Euler–Bernoulli theory to establish a mathematical model describing the relationship between water pressure and the bending deformation of the soft actuator. This model is then employed as a boundary condition when solving the dynamic model. Based on this, we use Cosserat rods theory to depict the dynamic behavior of the soft actuator's motion in an underwater environment. In particular, we analyze the impact of its own gravity, buoyancy, and water damping on the motion of the soft actuator. To validate the proposed dynamic model, we fabricated a novel fiber-reinforced soft actuator and a water-driven control system. Subsequently, we conducted a series of model validation experiments. Experimental results show the model maximum error rate is below 13%, thereby confirming the effectiveness of the model, which can predict the motion behavior of the soft actuator under different water-driven pressures.

The biomimetic soft robotic actuators can provide stable flexible multi-point contact to safely grip delicate objects. A lot of soft robotic actuators have been fabricated using silica gel materials through molding methods. However, owing to the difficulty of the demolding process, existing soft robotic arms are often designed to be short. To fabricate a long soft robotic arm, this paper proposes a novel design approach for fabricating the long soft robotic arm (1000 mm) inspired by the octopus arm that is a fiber-reinforced pneumatic elastomeric actuator. First, we develop a set of molds of the long soft robotic elastomeric actuator. To easily achieve the demolding of the soft actuator chamber, we design the three core petals around the mandrels in the molds. Furthermore, there are also two half-segment mandrels. The two half-segment mandrels are respectively removed from both ends of the mold when demolding. Then, we manufacture the long soft robotic arm using the molds by the combination silica gel and non-extensible materials. We also perform the experiments to verify the feasibility of the long soft robotic elastomeric actuator. The experimental results show the proposed design method for fabricating the long soft robotic arm is feasible.

Compared to rigid robotic actuators, soft actuators based on fiber-reinforced elastomeric actuators have great potential for use in exploring complex terrain, medical operations, and flexible capture of targets. However, it is still challenging to model the mechanical behavior of soft actuators because of the large deformation and nonlinear characteristics of elastic materials. This article proposes an analytical model to predict the shape of a soft actuator to better describe the relationship between its deformation and input pressure, gravity, and other external forces. We first derive the relationship between soft actuator deformation and pressure using volume maximization and the principle of virtual work. We further use Euler–Bernoulli beam theory to investigate the influence of self-gravity and external forces on the soft actuator configuration. The model is verified by fabricating a soft actuator prototype via mold casting. Finally, we perform a series of experiments to evaluate the accuracy of our proposed model. The longest total time to solve the model is 0.035 s. Experimental results show that the model's maximum error rate is between 2.89% and 9.75%. This indicates that the model can effectively predicts the deformation of soft actuators considering gravity and other external forces.

Unlike rigid actuators, soft actuators can easily adapt to complex environments. Understanding the relationship between the deformation of soft actuators and external factors such as pressure would enable rapid designs based on specific requirements, such as flexible, compliant endoscopes. An effective model is demonstrated that predicts the deformation of a soft actuator based on the virtual work principle and the geometrically exact Cosserat rod theory. The deformation process is analyzed for extension, bending, and twisting modules. A new manufacturing method is then introduced. Through any combination of modules, the soft actuator can have a greater workspace and more dexterity. The proposed model was verified for various fiber-reinforced elastomeric enclosures. There is good agreement between the model analysis and the experimental data, which indicates the effectiveness of the model.

Soft arms, characterized by their compliance and adaptability, have gained significant attention in applications ranging from industrial automation to biomedical fields. Modeling these systems presents unique challenges due to their high degrees of freedom, nonlinear behavior, and complex material properties. This review provides a comprehensive overview of three primary modeling approaches: numerical methods, analytical techniques, and data-driven models. Numerical methods, including finite element analysis and multi-body dynamics, offer precise but computationally expensive solutions for simulating soft arm behaviors. Analytical models, rooted in continuum mechanics and simplified assumptions, provide insights into the fundamental principles while balancing computational efficiency. Data-driven approaches, leveraging machine learning and artificial intelligence, open new avenues for adaptive and real-time modeling by bypassing explicit physical formulations. The strengths, limitations, and application scenarios of each approach are systematically analyzed, and future directions for integrating these methodologies are discussed. This review aims to guide researchers in selecting and developing effective modeling strategies for advancing the field of soft robotic arm design and control.

Fluid-filled fiber-reinforced elastomeric enclosures (FREEs) with a circular cross section, inspired by the muscle structure of octopus arms, are a popular choice for actuators because of their high power density and relatively low manufacturing cost. However, the shape, flexibility, and grasping force of FREEs are slightly different from those of real octopus arms. A soft arm with a semicircular cross section has better bending performance than that of FREEs with a circular cross section and can thus more easily achieve flexible grasping. In this paper, to better describe the deformation of soft arm shape in an underwater environment, a model based on a constrained maximization volume is proposed for a semicylindrical soft arm. In particular, the model takes into account the effect of the expansion of the bottom on the semicylindrical soft arm and the proposed analytical model is used to analyze the factors that affect the helix radius of the soft arm, including the helix angles of the fibers, wall thickness, and inner radius of the soft arm. Then a method for fabricating soft arms with a semicircular cross section (length: 700 mm) and a method for extracting the helix radius are also proposed. Finally, a series of driving experiments is performed to measure the accuracy of the model using a hydraulic platform. Experimental results show that the maximum error rate of the helix radius is between 8.99% and 12.29%. The helix radius can be varied from 74.3 mm to 176 mm by changing the parameters of the soft arm.