Soft robotics is a rapidly evolving field where robots are fabricated using highly deformable materials and usually follow a bioinspired design. Their high dexterity and safety makes them ideal for applications such as gripping, locomotion, and biomedical devices, where the environment is highly dynamic and sensitive to physical interaction. Pneumatic actuation remains the dominant technology in soft robotics due to its low cost and mass, fast response time, and easy implementation. Given the significant number of publications in soft robotics over recent years, newcomers and even established researchers may have difficulty assessing the state of the art. To address this issue, this article summarizes the development of soft pneumatic actuators and robots up until the date of publication. The scope of this article includes the design, modeling, fabrication, actuation, characterization, sensing, control, and applications of soft robotic devices. In addition to a historical overview, there is a special emphasis on recent advances such as novel designs, differential simulators, analytical and numerical modeling methods, topology optimization, data-driven modeling and control methods, hardware control boards, and nonlinear estimation and control techniques. Finally, the capabilities and limitations of soft pneumatic actuators and robots are discussed and directions for future research are identified.

Numerous soft grippers have been developed based on smart materials, pneumatic soft actuators, and underactuated compliant structures. In this article, we present a three-dimensional (3-D) printed omni-purpose soft gripper (OPSOG) that can grasp a wide variety of objects with different weights, sizes, shapes, textures, and stiffnesses. The soft gripper has a unique design that incorporates soft fingers and a suction cup that operate either separately or simultaneously to grasp specific objects. A bundle of 3-D-printable linear soft vacuum actuators (LSOVA) that generate a linear stroke upon activation is employed to drive the tendon-driven soft fingers. The support, fingers, suction cup, and actuation unit of the gripper were printed using a low-cost and open-source fused deposition modeling 3-D printer. A single LSOVA has a blocked force of 30.35 N, a rise time of 94 ms, a bandwidth of 2.81 Hz, and a lifetime of 26 120 cycles. The blocked force and stroke of the actuators are accurately predicted using finite element and analytical models. The OPSOG can grasp at least 20 different objects. The gripper has a maximum payload-to-weight ratio of 7.06, a grip force of 31.31 N, and a tip blocked force of 3.72 N.

Continued technological progress in robotic systems has led to more applications where robots and humans operate in close proximity and even physical contact in some cases. Soft robots, which are made of highly compliant and deformable materials, provide inherent safety features unlike conventional robots that are made of stiff and rigid components. Soft robotics is a rapidly developing field exploiting biomimetic design principles, novel sensor and actuation concepts, and advanced manufacturing techniques. In this study, we propose novel 3D printable soft vacuum actuators that are inspired by the sporangium of fern trees. These actuators that are directly manufactured using commercial and affordable fused deposition modeling 3D printers offer many advantages such as high actuation speed (5.54 Hz), long lifetime (123,000 cycles), large payload to weight ratio (∼26), and significant output forces (∼16 N). The behavior of these actuators is accurately predicted, and their performance is optimized using finite element modeling. Furthermore, diverse robotic applications such as locomotion robots (a walking robot moving with an average forward speed of v_f = 3.54 cm/s, and a hopping robot called Gongaroo hopping with an average speed of v_f = 3.75 cm/s), grippers, and artificial muscles have been established and activated using the new soft actuation concept. Finally, to demonstrate the modularity of the proposed actuation concept, soft actuators with multiple degrees of freedom and variable length are established using a series of 3D printable vacuum hinges.

Conventional robotic systems have proved their versatility in the industry where complex tasks requiring high force, high speed and high precision are desired. However, these rigid-bodied systems cannot collaborate safely with humans. Soft robots which are primarily made of highly compliant materials bring robots and humans together by operating safely in unstructured environments. Soft robots demand dexterous soft actuators that preserve or enhance their softness and safety features. This work reports on modeling, performance quantification and soft robotic applications of directly 3D printed linear soft vacuum actuators (LSOVA), that are manufactured in a single step, using a low-cost and affordable open-source fused deposition modeling 3D printer. Numerical and experimental results presented show that LSOVA have multiple advantages including high bandwidth (~6.49Hz), high output force (~27N) and long lifetime (~21,500 cycles). LSOVA blocked force and linear stroke can be predicted accurately using finite element and analytical models. Furthermore, LSOVA are scalable. The soft actuators can be either assembled in parallel as a bundle, where a linear relationship exists between the number of actuators and the output force or can be scaled up in terms of internal volume where a linear relationship exists between the output force and the internal volume of a single actuator. Finally, LSOVAs were tailored for various robotic applications including soft crawling robots for navigation in tubular systems, soft parallel manipulators for pick and place tasks, soft artificial muscles, soft prosthetic fingers for prosthetic hands and soft adaptive grippers for gripping applications.

The modeling of soft structures, actuators, and sensors is challenging, primarily due to the high nonlinearities involved in such soft robotic systems. Finite element modeling (FEM) is an effective technique to represent soft and deformable robotic systems containing geometric nonlinearities due to large mechanical deformations, material nonlinearities due to the inherent nonlinear behavior of the materials (i.e., stress-strain behavior) involved in such systems, and contact nonlinearities due to the surfaces that come into contact upon deformation. Prior to the fabrication of such soft robotic systems, FEM can be used to predict their behavior efficiently and accurately under various inputs and optimize their performance and topology to meet certain design and performance requirements. In this article, we present the implementation of FEM in the design process of directly three-dimensional (3D) printed pneumatic soft actuators and sensors to accurately predict their behavior and optimize their performance and topology. We present numerical and experimental results to show that this approach is very effective to rapidly and efficiently design the soft actuators and sensors to meet certain design requirements and to save time, modeling, design, and fabrication resources.