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Emerging actuators with various soft materials and a traveling wave motion are frequently discussed. Various configurations have been proposed and their resulting performances investigated, but it remains challenging to realize large strokes. This study presents an experimentally validated nonlinear finite element model to predict the deformation produced by a spiral pneumatic rubber actuator to generate a traveling wave motion. The actuator consists of a membrane mounted on a rubber substrate with three air chambers in a spiral configuration. The sequential deformations of the successive chambers interact with each other and produce radial traveling waves on the membrane surface, driving the objects placed on the actuator. Finite element analysis with ANSYS computer software was used to analyze the elastic movement by considering the influence of different initial structural types. The simulation results indicated an optimal structure with specific ratios. A reasonable correlation was obtained during experimental validation; the predicted displacement values were approximately 17% smaller than the experimental values. Finally, the transportation performance of the prototype was tested, and a velocity of 2.28 mm/s in the desired direction was achieved. We expect that our demonstration will expand the range of applications of the spiral pneumatic rubber actuator to include conveying or worm-like robots. [ABSTRACT FROM AUTHOR]

Pneumatic artificial muscles have some advantages. Especially, the flexibility of artificial muscles contributes to compose novel mechanisms. Authors succeeded in manufacturing novel soft mechanisms that are composed of only woven artificial muscles and strings. We called this mechanism active textile. The structure is uniformed with woven artificial muscles; nevertheless, the forms and movements of mechanisms are diverse. We aim to establish a design method for these active textiles. We reported that deformations of active textiles are changed by woven structures. In addition to that, wefts' characteristics such as cross-sectional shape, bending stiffness and elasticity determine the characteristic of a textile. Deformations of active textiles are caused by the contraction and the expansion of thin McKibben muscles. In this paper, authors focus on the contraction and curvature deformation of the active textile due to the drive of the artificial muscles.We fabricated active textiles with different wefts and different weave structures.Contraction and bending deformations of active textiles in the warp and weft directions are assumed geometrically. In addition, we verified the validity by experiments. [ABSTRACT FROM AUTHOR]

This letter describes the social needs and research trends of soft robots for pressure ulcer prevention, and our current work on the robotization of soft gel cushions. [ABSTRACT FROM AUTHOR]

This study aims to develop three-dimensional soft robots for special situations that cannot be easily resolved by normal hard-metal robots. We use an ion polymer–metal composite actuator, which is a soft actuator, moved using 1–10 V. The objective of our study is twofold: first, to develop a method to create 3D soft robots; and second, to develop a novel material to increase the performance of soft robots. The actuator fabricated using the proposed material exhibits a performance 113% higher than that of conventional actuators. [ABSTRACT FROM AUTHOR]

Displacement-amplified electromagnetic actuators (DAEAs) have been developed for efficiently using the electromagnetic attractive force by magnifying the motion of the change of a gap in which the electromagnetic attractive force is generated. This method enables us to use the large electromagnetic force with the gap being small for a larger stroke. This study applies DAEAs to an inchworm mechanism to realize motion on waving rails and precise positioning. A prototype was developed, and a fundamental experiment revealed the performance of the proposed inchworm mechanism. [ABSTRACT FROM AUTHOR]

One of the most important missions for robots is to operate in severe environments, and these situations require robots to have ‘toughness’ which can overcome large shocks, degraded communication quality, unexpected condition, and other critical accidents. Although there are many kinds of approaches to realize tough robotic systems, developing a tough actuators is one of the key technologies for them. We focus on hydraulic actuators and attempt to develop a tough robotic actuator with greater toughness than the electromagnetic actuators used in conventional robotic systems. In general, hydraulic actuators have enough toughness for severe environments, but their controllability and lightness are insufficient for robot systems. Herein, we propose novel hydraulic actuators that realizes lightweight with a multidirectional-forging magnesium alloy and have high controllability by low friction pistons. Prototypes were developed to examine the fundamental characteristics of the actuators and compare the two approaches for the low-friction pistons: one is based on a packing mechanism using an elastic restoring pressure, and the other utilizes a fluid-bearing technology. After basic experiments, the prototype was applied to a robotic leg to verify their potential in actual robotic systems. The robotic leg successfully jumped 260 mm in height with 21 MPa. [ABSTRACT FROM AUTHOR]

Conventional hydraulic actuators can generate a strong force due to high pressure. However, most of them are heavy and hard because they are made of metal. It is difficult to use such actuators in robots required to be as light as possible. Moreover, the joint mechanisms of these actuators have problems with intrinsic safety and robustness because the compliance is acquired using delicate sensors and advanced controls. Therefore, we propose a new rotational-compliant mechanism that allows the coexistence of strong force and compliance. The proposed mechanism has compliance in an active rotational direction and in two directions orthogonal to it. To realize this mechanism, we have developed a Hydraulic Artificial Muscle (HAM), which is very lightweight and able to generate strong force. Furthermore, the HAM has compliance without any advanced control. By exploiting the characteristics of the HAM, the function of the proposed mechanism can be realized even in conditions of compact dimensions. In this paper, by constructing a simple experimental system that imitates the proposed mechanism, and by modeling it, we verify its compliance from both a theoretical and an experimental point of view. We demonstrate that the mechanism has compliance in the three rotational directions. [ABSTRACT FROM AUTHOR]

Robots composed of hydraulic actuators have been utilized in various fields and at disaster sites. However, the hydraulic control system for multiple-degree-of-freedom mechanisms is large because such systems require many control components. The purpose of this research was to develop a small hydraulic flow control valve. This paper describes the fabrication and evaluation of a small three-way valve by particle excitation using a piezoelectric transducer. This valve consists of two transducers and can switch the inlet and outlet ports by applying an AC voltage of different driving frequencies to each transducer because each transducer has different resonant frequencies. The flow rate was controlled by applying a voltage to the piezoelectric transducer. We evaluated the vibration characteristics of the fabricated three-way valve. The vibration velocity exhibited peaks at 120 and 155 kHz for the inlet and outlet port, respectively, and that of each transducer increased with the applied voltage. Therefore, this three-way valve can switch the opening port by changing the driving frequencies and continuously controlling the flow rate. As a result, we have succeeded in driving the novel small three-way valve. [ABSTRACT FROM AUTHOR]

Current McKibben muscles are usually 10–40 mm in diameter, which makes them very stiff during contraction and difficult to deform rendering them unsuitable for dense mounting with shape adaptability in small spaces. In this research, to solve these problems, our group has developed the thinnest McKibben muscle reported until now. Bundling the muscles results in a multifilament muscle of the desired shape and flexibility. This paper reports the design of the thin McKibben muscle and the multifilament muscle and their static characteristics. In addition, we propose two theoretical models of multifilament muscles and derive their theoretical characteristics. The static characteristics of multifilament muscles with various design parameters have been evaluated through experiments and modeling. As a result, the greater contraction ratio of the multifilament muscles compared to that of the single muscle was demonstrated both theoretically and experimentally. [ABSTRACT FROM AUTHOR]

Pneumatic actuators in general require an air-compressor, valves, and pneumatic hoses. This makes them difficult to be used on mobile apparatus. To solve this problem, we previously developed a new gas source that uses the electrolysis/synthesis of water through an ion-exchange membrane. The developed gas source uses a gas/liquid reversible chemical reaction and controls the generation/absorption of gas through an electric current supplied to the membrane. In this paper, we present a control method for the energy-regeneration cycle and perform theoretical and experimental studies to verify its power consumption. This energy-regeneration control method is applied to an actuator, and it works successfully with a power consumption improvement of approximately 20% compared to that without energy-regeneration. Furthermore, we successfully develop a hose-free pneumatic rubber actuator with this control method. [ABSTRACT FROM AUTHOR]

This paper introduces a new type of linear actuator using the electromagnetic attractive force, which enables a submillimeter stroke. In general, actuation by the electromagnetic attractive force causes a tradeoff problem between the thrust force and the stroke because the thrust force depends on the gap between the electromagnet and the armature; an increase in the gap (stroke) drastically degrades the thrust force. To realize a submillimeter stroke while retaining a high thrust force, a structure that adopts a displacement amplification mechanism is proposed, which is often used to expand the stroke of a piezoelectric actuator. First, the electromagnetic attractive force is theoretically examined with and without displacement amplification. We verify that displacement amplification could create a higher thrust force and energy efficiency over a certain displacement. On the basis of this examination, a prototype actuator is designed, and the driving principle is illustrated. Further, an analytical model of the proposed actuator is developed for control and performance estimation. Several fundamental experiments with a developed actuator are performed in order to reveal the potential of the proposed actuator. The performance evaluations show that the maximum stroke is approximately 450 $\mu$m and a bandwidth greater than 300 Hz can be realized, and more a time constant is approximately 2 ms for a stroke of 450 $\mu$m. In addition, the experimental results were compared with the simulation results calculated from the analytical model to verify whether the prototype drives predictably according to the proposed concept under a dynamic situation. These results demonstrate that the proposed actuator enables good actuation performance, and it implies that there are tremendous advantages from the viewpoints of manufacturing, assembly, control, etc. [ABSTRACT FROM PUBLISHER]

Fluidic artificial muscles (FAMs), also known as McKibben actuators, are a class of fiber-reinforced soft actuators that can be pneumatically or hydraulically pressurized to produce muscle-like contraction and force generation. When multiple FAMs are bundled together in parallel and selectively pressurized, they can act as a multi-chambered actuator with bioinspired variable recruitment capability. The variable recruitment bundle consists of motor units (MUs)—groups of one of more FAMs—that are independently pressurized depending on the force demand, similar to how groups of muscle fibers are sequentially recruited in biological muscles. As the active FAMs contract, the inactive/low-pressure units are compressed, causing them to buckle outward, which increases the spatial envelope of the actuator. Additionally, a FAM compressed past its individual free strain applies a force that opposes the overall force output of active FAMs. In this paper, we propose a model to quantify this resistive force observed in inactive and low-pressure FAMs and study its implications on the performance of a variable recruitment bundle. The resistive force behavior is divided into post-buckling and post-collapse regions and a piecewise model is devised. An empirically-based correction method is proposed to improve the model to fit experimental data. Analysis of a bundle with resistive effects reveals a phenomenon, unique to variable recruitment bundles, defined as free strain gradient reversal. [ABSTRACT FROM AUTHOR]

Bodily self-consciousness has become an important topic in cognitive neuroscience aiming to understand how the brain creates a unified sensation of the self in a body. Specifically, full body illusion (FBI) in which changes in bodily self-consciousness are experimentally introduced by using visual–tactile stimulation has led to improve understanding of these mechanisms. This paper introduces a novel approach to the classic FBI paradigm using a robotic master–slave system which allows us to examine interactions between action and the sense of body ownership in behavioral and MRI experiments. In the proposed approach, the use of the robotic master–slave system enables unique stimulation in which experimental participants can administer tactile cues on their own back using active self-touch. This active self-touch has never been employed in FBI experiments and it allows to test the role of sensorimotor integration and agency (the feeling of control over our actions) in FBI paradigms. The objective of this study is to propose a robotic–haptic platform allowing a new FBI paradigm including the active self-touch in MRI environments. This paper, first, describes the design concept and the performance of the prototype device in the fMRI environment (for 3 T and 7 T MRI scanners). In addition, the prototype device is applied to a classic FBI experiment, and we verify that the use of the prototype device succeeded in inducing the FBI. These results indicate that the proposed approach has a potential to drive advances in our understanding of human body ownership and agency by allowing novel manipulation and paradigms. [ABSTRACT FROM AUTHOR]

Introduction: Robotic exoskeletons are emerging technologies that have demonstrated their effectiveness in assisting with Activities of Daily Living. However, kinematic disparities between human and robotic joints can result in misalignment between humans and exoskeletons, leading to discomfort and potential user injuries. Methods: In this paper, we present an ergonomic knee exoskeleton based on a dual four-bar linkage mechanism powered by hydraulic artificial muscles for stair ascent assistance. The device comprises two asymmetric four-bar linkage mechanisms on the medial and lateral sides to accommodate the internal rotation of the knee and address the kinematic discrepancies between these sides. A genetic algorithm was employed to optimize the parameters of the four-bar linkage mechanism to minimize misalignment between human and exoskeleton knee joints. The proposed device was evaluated through two experiments. The first experiment measured the reduction in undesired load due to misalignment, while the second experiment evaluated the device's effectiveness in assisting stair ascent in a healthy subject. Results: The experimental results indicate that the proposed device has a significantly reduced undesired load compared to the traditional revolute joint, decreasing from 14.15 N and 18.32 N to 1.88 N and 1.07 N on the medial and lateral sides, respectively. Moreover, a substantial reduction in muscle activities during stair ascent was observed, with a 55.94% reduction in surface electromyography signal. Discussion: The reduced undesired load of the proposed dual four-bar linkage mechanism highlights the importance of the adopted asymmetrical design for reduced misalignment and increased comfort. Moreover, the proposed device was effective at reducing the effort required during stair ascent., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Kittisares, Ide, Nabae and Suzumori.)

Complex and bulky driving systems are among the main issues for soft robots driven by pneumatic actuators. Self-excited oscillation is a promising approach for dealing with this problem: oscillatory actuation is generated from non-oscillatory input. However, small varieties of self-excited pneumatic actuators currently limit their applications. We present a simple, self-excited pneumatic valve that uses a flat ring tube (FRT), a device originally developed as a self-excited pneumatic actuator. First, we explore the driving principle of the self-excited valve and investigate the effect of the flow rate and FRT length on its driving frequency. Then, a locomotive robot containing the valve is demonstrated. The prototype succeeded in walking at 5.2 mm/s when the oscillation frequency of the valve was 1.5 Hz, showing the applicability of the proposed valve to soft robotics., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Nabae and Kitamura.)

Soft wearable robots could provide support for lower and upper limbs, increase weight lifting ability, decrease energy required for walking and running, and even provide haptic feedback. However, to date most of wearable robots are based on electromagnetic motors or fluidic actuators, the former being rigid and bulky, the latter requiring external pumps or compressors, greatly limiting integration and portability. Here we describe a new class of electrically-driven soft fluidic muscles combining thin, fiber-like McKibben actuators with fully Stretchable Pumps. These pumps rely on ElectroHydroDynamics, a solid-state pumping mechanism that directly accelerates liquid molecules by means of an electric field. Requiring no moving parts, these pumps are silent and can be bent and stretched while operating. Each electrically-driven fluidic muscle consists of one Stretchable Pump and one thin McKibben actuator, resulting in a slender soft device weighing 2 g. We characterized the response of these devices, obtaining a blocked force of 0.84 N and a maximum stroke of 4 mm. Future work will focus on decreasing the response time and increasing the energy efficiency. Modular and straightforward to integrate in textiles, these electrically-driven fluidic muscles will enable soft smart clothing with multi-functional capabilities for human assistance and augmentation., (Copyright © 2020 Cacucciolo, Nabae, Suzumori and Shea.)

This article presents an active textile braided in three strands with thin McKibben muscle. The fabrication of a textile using thin McKibben muscle as thread can be accomplished using a unique braiding method, developed in this study, to provide an active textile that shrinks along the transverse surface direction. This textile-type actuator is suitable as a type of soft robotic actuator for application in wearable robots and musculoskeletal robots because it is extremely lightweight, flexible, and easily applied to robot structures. In this article, the design and characteristics of a braided muscle in three strands, acting as the basic component of an active textile, as well as the design and static characteristics of the active textile, are presented. In addition, theoretical models are proposed for the active textile, and their theoretical characteristics are accordingly derived. The static characteristics of active textiles woven using various design parameters were then evaluated through experiments and modeling. The active textiles were found, both theoretically and experimentally, to provide a greater contraction ratio than a single muscle strand.