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Artificial muscles hold promise for safe and powerful actuation for myriad common machines and robots. However, the design, fabrication, and implementation of artificial muscles are often limited by their material costs, operating principle, scalability, and single-degree-of-freedom contractile actuation motions. Here we propose an architecture for fluid-driven origami-inspired artificial muscles. This concept requires only a compressible skeleton, a flexible skin, and a fluid medium. A mechanical model is developed to explain the interaction of the three components. A fabrication method is introduced to rapidly manufacture low-cost artificial muscles using various materials and at multiple scales. The artificial muscles can be programed to achieve multiaxial motions including contraction, bending, and torsion. These motions can be aggregated into systems with multiple degrees of freedom, which are able to produce controllable motions at different rates. Our artificial muscles can be driven by fluids at negative pressures (relative to ambient). This feature makes actuation safer than most other fluidic artificial muscles that operate with positive pressures. Experiments reveal that these muscles can contract over 90% of their initial lengths, generate stresses of ∼600 kPa, and produce peak power densities over 2 kW/kg—all equal to, or in excess of, natural muscle. This architecture for artificial muscles opens the door to rapid design and low-cost fabrication of actuation systems for numerous applications at multiple scales, ranging from miniature medical devices to wearable robotic exoskeletons to large deployable structures for space exploration.

Pneumatic artificial muscles (PAMs) are soft and flexible linear pneumatic actuators which produce human muscle like actuation. Due to these properties, the muscle actuators have an adaptable compliance for various robotic platforms as well as medical applications. While a variety of possible actuation schemes are present, there is still a need for the development of a soft actuator that is very light-weight, compact, and flexible with high power-to-weight ratio. To achieve this, the development of the PAM actuators has become an interesting topic for many researchers. In this review, the development of the different kinds of PAM available to date are presented along with manufacturing process and the operating principle. The various force models for artificial muscle presented in the literature are broadly reviewed with the constraints. Furthermore, the applications of PAM are included and classified based on the fields of biorobotics, medicine, and industry, along with advanced medical instrumentation. Finally, the needful improvements in terms of the dynamics of the muscle are discussed for the precise control of the PAMs as per the requirements for the applications. This review will be helpful for researchers working in the field of robotics and for designers to develop new type of artificial muscle depending on the applications.

We rethink the traditional reinforcement learning approach, which is based on optimizing over feedback policies, and propose a new framework that optimizes over feedforward inputs instead. This not only mitigates the risk of destabilizing the system during training but also reduces the bulk of the learning to a supervised learning task. As a result, efficient and well-understood supervised learning techniques can be applied and are tuned using a validation data set. The labels are generated with a variant of iterative learning control, which also includes prior knowledge about the underlying dynamics. Our framework is applied for intercepting and returning ping-pong balls that are played to a four-degrees-of-freedom robotic arm in real-world experiments. The robot arm is driven by pneumatic artificial muscles, which makes the control and learning tasks challenging. We highlight the potential of our framework by comparing it to a reinforcement learning approach that optimizes over feedback policies. We find that our framework achieves a higher success rate for the returns (100% vs. 96%, on 107 consecutive trials, see https://youtu.be/kR9jowEH7PY) while requiring only about one tenth of the samples during training. We also find that our approach is able to deal with a variant of different incoming trajectories.

Conventional robotic systems are built with rigid materials to deal with large forces and predetermined processes. Soft robotics, however, is an emerging field seeking to develop adaptable robots that can perform tasks in unpredictable environments and biocompatible devices that close the gap between humans and machines. Dielectric elastomers (DEs) have emerged as a soft actuation technology that imitates the properties and performance of natural muscles, making them an attractive material choice for soft robotics. However, conventional DE materials suffer from electromechanical instability (EMI), which reduces their performance and limits their applications in soft robotics. This review discusses key innovations in DE artificial muscles from a material standpoint, followed by a survey on their representative demonstrations of soft robotics. Specifically, we introduce modifications of DE materials that enable large strains, fast responses, and high energy densities by suppressing EMI. Additionally, we examine materials that allow variable stiffness and self‐healing abilities in DE actuators. Finally, we review dielectric elastomer actuator (DEA) applications in soft robotics in four categories, including automation, manipulation, locomotion, and human interaction. Dielectric elastomers are an emerging soft actuation technology that imitates the properties and performance of natural muscles, making them an attractive material choice for soft robotics. In addition, their soft nature allows diverse configurations such as stacks, spring rolls, rolls, and balloons, allowing creative and flexible designs for soft robotic applications.

Implantable artificial muscles are of great importance for muscle function restoration and physical augmentation but are still challenging. Herein, we report an artificial muscle by soaking-polymerization of polyaniline (PANI) inside a carbon nanotube (CNT) yarn. Working in aqueous biocompatible solutions, the yarn muscle generates a large contractile stroke of 17% and high isometric stress of 8 MPa at voltages lower than 2 V. The excellent performance can be ascribed to the large actuation volume that is enabled by the fast electrochemical redox of PANI confined in a coiled yarn structure. The actuation performance outperforms that of previously reported aqueous artificial yarn muscles. Moreover, the yarn muscle can work well and maintain excellent actuating performance in other biocompatible solutions such as normal saline and Na 2 SO 4 aqueous solution, which makes the CNT/PANI yarn muscles suitable for implantable bionic applications. Finally, a biomimetic arm was fabricated to demonstrate the applications of the CNT/PANI yarn artificial muscle in implantable muscle, underwater robots, and soft exoskeletons.

An effective and rapid response of muscle contraction and relaxation is crucial for performing appropriate body gaits, including movements of the arms and legs. Any deformation in the muscles can disrupt gait stability, making muscle movement difficult. The arm, consisting of the radius, ulna, and humerus, can be modeled as mechanically jointed pendulums, with tensions from the arm muscles varying during contraction and relaxation. In a static state, the muscles maintain constant tension and length, even when external gravitational force is applied to the hand. This study presents a system in which a pair of jointed pendulums is driven by artificial muscles, represented by flexible ropes wound around the edge of an electronic motor’s wheel. Muscle movement is simulated through the adjustment of the length of the flexible ropes attached to the motor. Switching between the clockwise and counterclockwise rotation of the motor modifies the length of the flexible ropes, thereby altering the intrinsic tensions to control arm movements. Electrical signals from a simple neural circuit are used to control the rotation of the electronic motor, enabling the regulation of muscle movement in the arm model by adjustable flexible ropes. The stability criterion for the electromechanical arm is derived, and the interactions among the neural circuit, electronic motor, and jointed pendulums are examined in detail. The results and proposed scheme can contribute to the design of controllable artificial arms, providing potential assistance to disabled arms by incorporating auxiliary artificial muscles.

Recently, robotics and wearable technology have increased demand for actuators capable of delivering flexible and adaptive motions that rigid mechanisms cannot provide. Twisted and coiled polymer actuators (TCPAs) made from nylon fishing lines show promise owing to their low cost, ease of fabrication, and high deformation capabilities. However, conventional heating methods using copper or nichrome wires are frequently limited by low thermal response rates and durability issues. In this study, we introduce a new heating technique in which five conductive fibers are twisted together and uniformly wrapped around the TCPA to improve heat transfer efficiency and allow operation at higher input voltages. In addition, we propose a unit design that bundles multiple TCPAs into a helical fiber structure (CF‐HFS TCPA) for increased force generation. Experimental results show that the performance of single TCPA_CF units is strongly dependent on wire gauge: under light loads of approximately 1.96–2.45 N, finer wires achieve higher displacement ratios at high voltages, whereas under loads of approximately 2.94 N, their performance declines, while thicker wires maintain stable operation over a wider load range. Temperature measurements show that, while gauges achieve high surface temperatures under light loads, the temperature rise is reduced under heavy loads owing to reduced contraction and increased heat dissipation. Overall, these findings support the potential utility of our approach as an effective method for developing actuators for soft robotic and wearable applications.

Soft continuum robots, characterized by their dexterous and compliant nature, often face limitations due to buckling under small loads. This study explores the enhancement of axial performance in soft robots intrinsically actuated with extensile fluidic artificial muscles (EFAMs) through the incorporation of bio-inspired radial supports, or ossicles. By conducting quasi-static force response experiments under varying pressure conditions (103.4–517.1 kPa), and a modified Euler column buckling model, we demonstrate that ossicles significantly increase the robots’ resistance to buckling, thereby extending their application scope in payload-carrying tasks. These findings not only underscore the effectiveness of ossicle reinforcement in improving structural robustness but also pave the way for future research to optimize soft robot design for enhanced performance.

The aim of the present work was to select the thickness of a silicone layer coating a PES woven fabric designed for application in the artificial transverse muscles as a component of the medical robot. The artificial muscle in the form of U-shaped tube is subjected to repeated bending. Due to this fact, an important task was to ensure fatigue resistance to the bending of the muscle component. The fatigue bending was performed using the STM 601/12 device manufactured by SATRA Technology, Northamptonshire, UK. The surface geometry of the fabric before and after coating, as well as after 4000, 10,000 and 20,000 cycles of bending, was assessed using the MicroSpy® Profile profilometer manufactured by the FRT, the art of metrology, Bergisch Gladbach, Germany. Additionally, the microscopic observations of fabric surface were performed after the abovementioned cycles of fatigue bending. The results obtained showed that in order to ensure the required functionality of the coated fabric, the 0.2 mm silicone layer is better than the 0.1 mm silicone layer.

This study proposes a method for improving the performance of a manipulator driven by pneumatic artificial muscles. Although the straight-fiber-type pneumatic artificial muscle (SF-PAM), a kind of pneumatic artificial muscle, is lightweight and exhibits high contractile force and contraction percentage, its contractile force decreases as contraction increases. To compensate for the decrease in the SF-PAM contractile force, we developed a noncircular pulley and integrated it into the manipulator driven by a wire pulley mechanism. Because this noncircular pulley is designed in accordance with the output characteristics of SF-PAM, the contraction force of SF-PAM can be converted into manipulator torque efficiently. In addition, the radius of the noncircular pulley is expressed as a function, which can be incorporated into a numerical model for the manipulator’s controller. Subsequently, simulation and experimentation to verify the proposed method showed that, when using the same actuator, the manipulator with a noncircular pulley can optimize both output torque and range of motion better than that with a conventional circular pulley. However, a few differences between simulation results and experimental results were observed. These differences were caused by SF-PAM stretching which was not considered in the model. This drawback can be overcome by improving the SF-PAM and the numerical model in future studies. We believe that this study will provide designers of robots that coexist with humans with a high degree of freedom.