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McKibben pneumatic actuators (MPAs) are soft actuators that exert tension by inflating a rubber tube with compressed air. Although electropneumatic regulators can control air pressure, their cost and size limit their applications. This study employs a dynamic quantizer to control an MPA using a small solenoid valve that can only open or close, as opposed to an electropneumatic regulator. A dynamic quantizer is a type of quantizer that converts continuous signals into discrete signals. Our previous study confirmed that the tension or length control of MPA can be achieved using a dynamic quantizer. As MPA exerts force only in the direction of contraction, multiple MPAs must be combined when using them as robot actuators. This study demonstrates that control using a dynamic quantizer is feasible, even when multiple MPAs are employed. We focused on a pendulum driven by two MPAs to achieve angle-tracking control using a dynamic-quantizer-based control method. The results of numerical simulations and experimental tests confirm that the angle of the pendulum can be controlled using MPAs with a dynamic quantizer.

A McKibben-type pneumatic actuator (MPA) is a soft actuator that generates tension by inflating a rubber tube with compressed air. Electropneumatic regulators are typically employed to regulate air pressure in MPAs. However, they are normally large in size and expensive, which are significant obstacles to the autonomous decentralized control of many MPAs in achieving various robot motions. In this study, the exerted tension of the MPA was controlled using a small solenoid valve that could be opened and closed instead of an electropneumatic regulator. To achieve this tension control, we proposed the use of a dynamic quantizer that converts continuous pressure values into discrete pressure values and controls the solenoid valve based on the discretized pressure values. The proposed method was applied to feedforward and feedback control of the exerted MPA tension under isometric conditions. Experiments on an actual device with a small solenoid valve demonstrated the effectiveness of the proposed method based on a dynamic quantizer.

Recently, soft actuators have gained considerable attention owing to their flexibility and high output-to-weight ratios. The McKibben pneumatic actuator (MPA), a type of soft artificial muscle, is an actuator that generates force by inflating a rubber tube with compressed air. Conventional MPAs, such as linear actuators, generate force along straight lines; hence, achieving complex movements, such as bending using a single muscle, can be challenging. In this study, we enabled bending movements in MPA by applying an elastic adhesive coating to MPA. Experimental results demonstrated that the coated MPA successfully performed bending movements. Furthermore, we confirmed that the curvature and fiber angles of the coated and uncoated surfaces changed with applied pressure, thereby indicating that the adhesive can be used to control the fiber angles and achieve the desired curvature.

Pneumatic artificial muscles (PAMs) are soft actuators that generate tension via contraction when supplied with compressed air. Although PAMs have been widely used in robots mimicking endoskeletal organisms, recent advancements in millimeter-scale thin PAMs have enabled a more precise replication of complex musculoskeletal systems. In contrast, exoskeletal organisms, such as crustaceans and insects actuate their joints using pennate muscles embedded within their exoskeletons. However, integrating actuators into the exoskeletons of exoskeletal-inspired robots is challenging owing to spatial constraints. Consequently, wire and servo-driven mechanisms are predominantly employed, and studies on exoskeletal robots incorporating the muscle-apodeme structures of exoskeletal organisms remain largely unexplored. To address this gap, this paper presents the development of a crab-inspired robotic walking leg featuring an exoskeletal structure with embedded pneumatic artificial pennate muscles, modeled after the muscle-apodeme structures of snow crabs. The experimental evaluations demonstrated that the robot successfully performed joint opening and closing motions, achieving a range of motion comparable to that of a snow crab.

McKibben pneumatic actuators (MPAs) are soft actuators that exert tension by applying compressed air to expand a rubber tube. Although electro-pneumatic regulators can control air pressure, most are large and expensive. This study utilizes a dynamic quantizer to control the MPA with a small solenoid valve that can only open and close the valve instead of an electro-pneumatic regulator. A dynamic quantizer is one of the quantizers that converts continuous signals to discrete signals. Our previous study confirmed that tension control of MPA under isometric conditions could be realized using a dynamic quantizer. However, it is often necessary to control the length of the MPA as well as the tension of the MPA. This study implements a dynamic quantizer to control the length of the MPA with a small solenoid valve. Numerical simulations and experimental tests verify the effectiveness of the proposed method. The results of the numerical simulations and experimental tests confirmed that the length of the MPA can be controlled using the dynamic quantizer.

The McKibben pneumatic actuator (MPA) is a soft actuator used for performing various practical functions in robots. Particularly, many dynamic robots have been realized using MPAs. However, there is a trade-off between torque generated by MPA and the range of motion of the joint. In this study, we focus on the jumping motion of a leg-type robot and use an elliptical pulley whose moment arm changes depending on the robot’s posture. To confirm the effectiveness of the elliptical pulley, the relationship between the knee joint pulley (patella) shape and jumping height was analyzed by simulation, and the shape of the patella maximizing jumping height was determined. It was shown that an elongated elliptical patella shape is more effective for the jumping motion than a circular one. Furthermore, the effectiveness of the analytically determined patella shape was confirmed by experiments using an actual robot.

The McKibben Pneumatic Actuator (MPA) is well-known as a type of soft actuator. As MPA generates tension only in the direction of compression, it is necessary to construct an antagonistic structure to drive a joint by MPAs and to coordinate antagonized MPAs. Similar to MPA, muscles in animals also generate tension only in the direction of contraction. Some studies have reported that animals utilize tension information to coordinate muscles for various autonomous movements. The purpose of this study is to realize autonomous cooperation between antagonized MPAs by applying tension feedback control and analyzing the mechanism of coordination. For this purpose, we verify the effect of tension feedback control on the 1-DOF pendulum model with antagonized MPAs. First, through numerical simulations, it is confirmed that the tension feedback generates various coordinated movements of antagonized MPAs, and the pendulum exhibits a bifurcation phenomenon based on the phase difference of the inputs of MPAs. Thereafter, we develop an actual experimental machine based on the model and confirm the autonomous cooperation between actual MPAs through verification experiments similar to the numerical simulations.

In general, legged robots are designed to walk with a fixed rhythmic pattern. However, most animals can adapt their limb movements while walking. It is necessary to understand the mechanism of adaptability during locomotion when designing bio-inspired legged robots. In this paper, we propose an approach to analyze the flexible locomotion pattern of animals using a polar histogram. Field crickets were used to investigate variations in leg movement of insects depending on the environment. Crickets have a tripod gait; however, their leg movement changes depending on the texture of the ground. There was a significant difference between the leg movement when walking and when swimming. Our approach can explain how animals move their legs during locomotion. This study is useful for evaluating the movements of legged robots.

Abstract The cricket is one of the model animals used to investigate the neuronal mechanisms underlying adaptive locomotion. An intact cricket walks with a tripod gait, similar to other insects. The motor control center of the leg movements is located in the thoracic ganglia. In this study, we investigated the walking gait patterns of crickets whose ventral nerve cords were surgically cut to gain an understanding of how the descending signals from the head ganglia and ascending signals from the abdominal nervous system into the thoracic ganglia mediate the initiation and coordination of the walking gait pattern. Crickets whose paired connectives between the brain and subesophageal ganglion (SEG) were cut exhibited a tripod gait pattern. However, when one side of the connectives between the brain and SEG was cut, the crickets continued to turn in the opposite direction to the connective cut. Crickets whose paired connectives between the SEG and prothoracic ganglion were cut did not walk, whereas the crickets exhibited an ordinal tripod gait pattern when one side of the connectives was intact. Crickets whose paired connectives between the metathoracic ganglion and abdominal ganglia were cut initiated walking, although the gait was not a coordinated tripod pattern, whereas the crickets exhibited a tripod gait when one side of the connectives was intact. These results suggest that the brain plays an inhibitory role in initiating leg movements, and that both the descending signals from the head ganglia and the ascending signals from the abdominal nervous system are both important in initiating and coordinating insect walking gait patterns. Competing Interest Statement The authors have declared no competing interest.

Brittle stars (Echinodermata: Ophiuroidea) digest a great diversity of food in their stomach, which widely lies in the central disk. As for a possible digestive activity, the green brittle star Ophiarachna incrassata (Lamarck, 1816) is known to show a dynamic movement at the disk. This phenomenon would deeply involve the morphological structure of the stomach. However, past anatomical studies have shown the digestive system in two dimensions after wide incision of the body wall anchoring the stomach. This methodology restrains us from understanding how the stomach actually shapes inside a brittle star. We aim to visualize the morphology of brittle stars' digestive system in a non-destructive and three-dimensional way, with a comparison between a relaxed specimen and a specimen fixed at the very moment of the disk's movement. Employing X-ray micro-computed tomography (micro-CT) and introducing an instant freezing method with cryogenic ethanol, we found the stomach wholly transformed during the movement. We here brought transparency to the in vivo position of gut contents to hint the mechanism and digestive function of the movement. Our outcome spotlights a dynamic digestive process in echinoderms and a widely applicable method for probing into its relation with body structure.