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Dielectric elastomer actuators (DEAs) have been shown to produce electrically induced strains beyond 500%. The ability to undergo large deformation allows the DEA to store large amounts of elastic energy by electrical actuation; it also allows the DEA to perform flexibly in a diverse range of motions. Existing studies used different methods to maximize actuation strain for soft robotic applications. In this article, we examine the actuation of our antagonistically coupled DEAs, reminiscent to that of human muscles. We perform an analysis to reveal optimal conditions that maximize its actuation stroke, actuation force, and output energy. We quantify actuation stroke by the displacement sweep due to electrical actuation, between two fixed points, expressed as a percentage, and refer to this as "actuation sweep." From the analysis, we predicted an optimal prestretch for the DEA that corresponds to a 59% actuation sweep. In our experiment, we realized a 55% actuation sweep. We further characterized the output force and the mechanical work done for complete performance appraisal of the antagonistic system both theoretically and experimentally. We realized an antagonistic soft actuator system with simple geometry that provides significant electrically induced displacement, force, and work done, similar to that of biological muscle systems, and demonstrated its efficacy.

Pneumatic artificial muscles (PAMs) are an extensively investigated type of soft actuator. However, the PAM motions have been limited somewhat to uniaxial contraction and extension, restraining the development of PAMs. Given the current strong interest in soft robotics, PAMs have been gaining renewed attention due to their excellent compliance and ease of fabrication. Herein, under the inspiration of the elephant trunk, a family of bending and helical extensile PAMs (HE-PAMs)/helical contractile PAMs (HC-PAMs) was proposed and analyzed. Through both experiment and analysis, a model of generalized bending behavior of PAMs was built and developed to investigate the properties of axial, bending, and helical PAMs in the same theoretical framework. The topological equivalence and bifurcation were found in the analysis and utilized to explain the behaviors of these different PAMs. Meanwhile, a coupled constant curvature and torsion kinematics model was proposed to depict the motion of PAMs more accurately and conveniently. Moreover, a soft tandem manipulator consisting of bending and helical PAMs was proposed to demonstrate their attractive potential.

The improvement of the load capacity of soft robotic grippers has always been a challenge. The load improvement methods of existing soft robotic grippers mainly include the development of soft actuators with high output force and the creation of closed gripping structures. Inspired by winding behaviors of animals and plants, we propose a high-load soft robotic gripper driven by pneumatic artificial muscles (PAMs) that combines the advantages of a high force soft actuator and a closed gripping structure. Most existing model formulations focus on characterizing the end force generated to the length contraction and applied pressure of PAMs. However, the focus of this work is to build the force model of PAMs in winding shape to analyze the tightening force of the high-load soft gripper, and the model is validated by a tightening force test. An experimental work is carried out to characterize the load capacity and multi-object gripping capacity of the high-load soft gripper. We experimentally prove that it can lift heavy objects that weigh up to 35.5 kg, which is more than 47 times its weight. This work contributes to the load improvement of soft robotic grippers, and the mathematical modeling of engineering systems with winding structures. The developed high-load soft gripper is expected to enter the practical application field from the laboratory.

Soft robots have been a buzz word in the field of robotics. However, there are several definitions of soft robots in literature with their varying degrees of usefulness to providing guidelines for designing and constructing a soft robot. This paper attempts to provide a comprehensive definition of soft robots with the goals that the definition should be of (i) generality and (ii) practicality. By generality, it is meant that the definition gives the signature to soft robots and is all inclusive, and by practicality, it is meant that the definition provides a general guideline for practicing designers to design and construct soft robots to particular applications. A salient point in our definition of soft robots is the concept of softness, which is defined from the perspective of a receiving object - particularly as the stress and other damage quantities (e.g., deflection) created in the receiving object when the receiving object interacts with the soft system per se. A further contribution is the provision of definitions to soft sensor, soft actuator along with power generator, soft controller, and soft mechanism. Finally, research issues on soft robots are outlined.

In the 21st century, robotics has been revolutionized by a new perspective: robots made of soft materials mimicking nature show several advantages compared to hard robot counterparts, leading to the birth and quick spread of a new scientific field named soft robotics. Due to the unconventional materials used in soft robotics (not only soft materials but also conductive, magnetic, and other materials employed for soft robot actuation), the manufacturing process is the basis by which to obtain soft structures able to meet specific requirements and save time and cost. The present paper aims to give a review of the current use of additive manufacturing (AM) methods for the manufacturing of soft robots. AM, also known as 3D printing, is characterized by several features, such as the possibility to easily produce very complex geometries, which are well suited for soft robot fabrication. The authors, after providing a summary of the most used actuation systems in soft robots, classify the use of AM technologies in soft robotics, investigating the most important and recent works in this field, as a function of how these technologies are employed in the whole soft robot manufacturing cycle. With this in mind, the authors found three approaches to exploit AM in soft robotics: rapid mold fabrication (AM plays a passive role), hybrid (AM plays an active role but manufacturing technologies other than AM are still used), and total additive manufacturing (only AM technologies are used). Only the latter approach takes full advantage of AM, although the other two still provide benefits. With new developments in commercial 3D printing systems (machines and materials) aimed at the fabrication of soft and unconventional parts, AM is set to become the manufacturing technology of the future in the soft robotics field, overcoming traditional manufacturing methods such as molding and soft lithography.

Advancements in software engineering have enabled the robotics industry to transition from the use of giant industrial robots to more friendly humanoid robots. Soft robotics is one of the key elements needed to advance the transition process by providing a safer way for robots to interact with the environment. Electroactive polymers (EAPs) are one of the best candidate materials for the next generation of soft robotic actuators and artificial muscles. Lightweight dielectric elastomer actuators (DEAs) provide optimal properties such as high elasticity, rapid response rates, mechanical robustness and compliance. However, for DEAs to become widely used as artificial muscles or soft actuators, there are current limitations, such as high actuation voltage requirements, control of actuation direction, and scaling, that need to be addressed. The authors&rsquo, approach to overcome the drawbacks of conventional DEAs is inspired by the natural skeletal muscles. Instead of fabricating a large DEA device, smaller sub-units can be fabricated and bundled together to form larger actuators, similar to the way myofibrils form myocytes in skeletal muscles. The current study presents a novel fabrication approach, utilizing soft lithography and other microfabrication techniques, to allow fabrication of multilayer stacked DEA structures, composed of hundreds of micro-sized DEA units.

Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics., National Science Foundation (U.S.) (Grant IIS-1226883)