Review of soft fluidic actuators: classification and materials modeling analysis

Abstract

Soft actuators can be classified into five categories: tendon-driven actuators, electroactive polymers (EAPs), shape-memory materials, soft fluidic actuators (SFAs), and hybrid actuators. The characteristics and potential challenges of each class are explained at the beginning of this review. Furthermore, recent advances especially focusing on soft fluidic actuators (SFAs) are illustrated. There are already some impressive SFA designs to be found in the literature, constituting a fundamental basis for design and inspiration. The goal of this review is to address the latest innovative designs for SFAs and their challenges and improvements with respect to previous generations, and help researchers to select appropriate materials for their application. We suggest six influential designs: pneumatic artificial muscles (PAM), PneuNet, continuum arm, universal granular gripper, origami soft structure, and vacuum-actuated muscle-inspired pneumatic (VAMPs). The hybrid design of SFAs for improved functionality and shape controllability is also considered. Modeling SFAs, based on previous research, can be classified into three main groups: analytical methods, numerical methods, and model-free methods. We demonstrate the latest advances and potential challenges in each category. Regarding the fact that the performance of soft actuators is dependent on material selection, we then focus on the behaviors and mechanical properties of the various types of silicone which can be found in the SFA literature. For a better comparison of the different constitutive models of silicone materials which have been proposed and tested in the literature, ABAQUS software is here employed to generate the engineering and true strain-stress data from the constitutive models, and compare them with standard uniaxial tensile test data based on ASTM412. Although the figures presented show that in a small range of stress-strain data, most of these models can predict the material model acceptably, few of them predict it accurately for large strain-stress values.

3D printing programmable liquid crystal elastomer soft pneumatic actuators

“…Although diverse technologies have been developed for constructing SPAs, the soft materials used in SPAs are mainly isotropic, such as silicone rubber. 13 To create mechanical anisotropy in the isotropic base materials, two traditional strategies are usually used. One is to apply high-strength materials as restraining elements, which can be attached to the surface of the actuators or embedded within.…”

Design, Fabrication and Analysis of Magnetorheological Soft Gripper

“…The soft grippers can be dived into groups based on the method of actuation such as pneumatic, hydraulic, magnetic field or electric field [ 2 , 13 ]. One of the most interesting method of building soft grippers is application of soft fluid actuators [ 16 ] which can be driven by pneumatic or hydraulic excitation. In recent times, these soft grippers has been extensively developed and had a commercial application like PneuNets [ 17 ].…”

Characterization of bending balloon actuators

“…Introduction of the fluid inflates the chamber, and the expansion pressure generated within the chamber leads to movement of the body resulting in large and fast deformation. Classification of soft actuators and design strategies to achieve different types of actuations have been reviewed in detail ( Gorissen et al, 2017 ; Pagoli et al, 2021 ; Xavier et al, 2022 ). Balloon actuators are designed to undergo various movements such as expansion, contraction, twisting, and bending ( Fujiwara et al, 2009 ; Marchese et al, 2015 ; Schaffner et al, 2018 ; Balak and Mazumdar, 2020 ).…”

“…Various strategies can be used to vary the wall compliance such as changing the geometry, using different materials, or incorporating constraints such as inextensible fibers (fiber-reinforced bending actuators) ( Polygerinos et al, 2015 ). By connecting multiple bending balloon actuators in series, advanced functionalities such as gripping and locomotion can been achieved ( Shepherd et al, 2011 ; Zolfagharian et al, 2020 ; Pagoli et al, 2021 ). Most of the balloon actuator assisted soft robotics are focused largely on the type of movement.…”