This study aims to develop a single mobile robot capable of navigating confined spaces characterized by non-circular cross-sections, embedded obstacles, and bends that are difficult for human access. To this end, we propose the Multi-Flexible Wheel Robot using brushes and elastic springs. The robot can adapt its body shape to the surrounding geometry and rotate along the meridional direction, enabling it to traverse a wide range of complex environments. This paper presents the conceptual design and driving model of the Multi-Flexible Wheel Robot, along with experimental results obtained using an initial prototype in confined space locomotion tests. In the tests, the robot traversed a straight duct with a 250 mm inner diameter and 1000 mm length in 13 s, a similar duct containing obstacles in 23 s, and a duct with varying cross-sectional geometry in 19 s. These results demonstrate the robot can transmit rotational force to multiple brushes via a deformable ring-shaped elastic structure, enabling it to autonomously navigate confined spaces that include non-circular cross-sections, obstacles, and bends.

This study aims to develop an autonomous decentralized motion generation system that adapts to the state of the target material to be mixed and transported within a peristaltic pump designed in a manner analogous to intestinal peristalsis. The authors investigate the discrepancy function, which serves as a control law for modular snake-and amoeba-type robots, and propose a method for achieving autonomous decentralized control by regulating the phases corresponding to the supply and exhaust states within each unit of the peristaltic pump. The application of the local feedback term g(θi) was experimentally verified using a two-unit coupled pump to investigate the transition from in-phase motion to mixed-phase motion. The results showed that the phase difference between the units transitioned from in-phase (0 rad) to anti-phase (π rad), demonstrating that the local feedback term induces a phase delay and enables the desired mixed motion. In addition, by applying a control law based on the discrepancy function to the material whose viscosity decreases as mixing progresses, the pump's motion pattern was observed to transition in response to the mixing state of the material. As a result, the motion pattern shifted from mixing motion to peristaltic motion approximately 230 s after the start of mixing. These findings indicate that the pump autonomously and in a decentralized manner switched its motion pattern in accordance with the internal state of the material.

This study develops an autonomous cleaning robot designed to remove accumulated grease in restaurant kitchen ducts, where human access and manual cleaning are not feasible. Prior studies have developed cleaning mechanisms for round ducts employing planetary gear systems, demonstrating their efficiency in grease removal. However, these systems lack propulsion mechanisms, and cleaning experiments have been limited to short-distance, small-diameter pipes (140 mm, 100A). Therefore, no system has been developed for cleaning grease in long-distance, large-diameter ducts in real-world environments. To address this limitation, we developed a self-propelled cleaning robot integrating a planetary gear-based cleaning mechanism and an inchworm-inspired propulsion mechanism. The design of the propulsion mechanism involved modeling brush rotational torque, gripping torque, and gripping force. Based on this model, a duct inspection and cleaning robot equipped with both propulsion and cleaning mechanisms was developed. Subsequently, the developed robot was tested in a 9 m mock-up duct to evaluate its self-propelled cleaning performance. The robot removed an average of over 85% of the grease under all test conditions while operating autonomously. Finally, a cleaning experiment was conducted in a butcher shop duct, where the robot removed most of the adhered grease. These experiments demonstrated that the developed robot can autonomously clean and inspect ducts in real-world environments where human entry is impractical.

This study proposed a peristaltic motion-type inspection robot equipped with a "linear antagonistic mechanism using artificial muscles with an endoskeletal structure" to amplify propulsion and traction. We sought to develop an in-pipe inspection robot for long, narrow, and complex pipes requiring large propulsion, traction, and flexibility. In a previous study, we proposed a linear antagonistic mechanism allowing the inspection robot to generate both high propulsion and traction along with flexibility in narrow pipes. The proposed mechanism consisted of two extension actuators and a gripping actuator sandwiched between these extension actuators. The large extension force by the extension actuators is distributed to both propulsion and traction. However, owing to the piston-shaped configuration of the extension actuators, the generated force decreased in a manner dependent on the cross-sectional area within narrow pipelines. Therefore, the in-pipe inspection robot took time to move in long-distance, small-diameter pipes with multiple bends. This paper describes a "linear antagonistic mechanism using artificial muscles with an endoskeletal structure" that amplifies propulsion and traction by inserting a tension spring (skeleton) inside the contraction actuators (artificial muscles) and utilizing the action force generated by the actuator and transmitted by the tension spring. In this study, the developed robot with an endoskeleton exhibited maximum propulsion of 60.2 N, surpassing its non-endoskeleton counterpart by a factor of 1.61. Furthermore, the robot equipped with the endoskeleton passed through an elbow pipe 1.29 times faster than that without the endoskeleton, reducing the time from 741 to 576 s. The function value that compares the propulsion and traction considering the effects of the applied pressure and pipe diameter required for long-distance inspection was more than 1.13 times that of the previous study. In addition, the non-dimensionalized traction was 1.55 times greater than that of any other pipe inspection robot, and the propulsion was large enough to pass through a bending pipe. This result indicates the feasibility of the developed robot for inspecting long, narrow, and complex pipes.

In this paper, we describe the development of short-fiber oriented rubber and its application to elongation-type actuators. Short-fiber oriented rubber, i.e., rubber containing oriented short fibers with lengths of 3 mm, has anisotropy in the direction of fiber orientation. In a previous study, it was shown that short fiber-reinforced artificial muscles made of short-fiber oriented rubber can achieve up to 17% shrinkage. However, in that study, characteristics other than the amount of shrinkage were not measured, the basic characteristics of the developed artificial muscle were unclear, and the shrinkage ratio was smaller than that for existing straight-fiber-type artificial muscle. In the present study, we developed a new method for fabricating short-fiber oriented rubber and measured the tensile characteristics in the direction of fiber orientation and vertical to the orientation direction. Moreover, we developed an elongation-type artificial muscle from the rubber sheet and measured its elongation characteristics. Test results indicated that the fabricated rubber sheet had anisotropy. They also indicated that the anisotropy increased with the fiber concentration and that the fiber restraint acted not only in the orientation direction but also in the vertical direction. Furthermore, the developed elongation-type artificial muscle was three times more anisotropic in the ratio of axial changes to diametral changes. On the basis of these results, we expect to develop an automated production method for soft actuators.

An anchoring mechanism was designed for an earthworm-type robot that can inspect without slipping in sewage or oil pipes. A conventional robot moves through pipes making use of the friction between its surface and the inner surfaces of the pipes. It is difficult for the robot to inspect in pipes where viscous liquid remains. Therefore, a mechanism for inspecting in slippery pipes was developed. A mixture of rubber dough and antislip material was used to produce enhanced frictional force. Three types of antislip were compered based on measurements of the coefficient of friction. The highest frictional coefficient was generated by the material mixed with the largest blast material. The developed anchoring mechanism applying the material increased the frictional coefficient by 3.59 times compared with conventional anchoring mechanisms. These results provide innovative insights into the development of inspection robots in challenging environments, such as those in which anchoring is difficult.

The cleaning of residential ventilation ducts is necessary to prevent damage to health. However, since residential ventilation ducts are usually thin and curved, cleaning them is difficult. It is also difficult to obtain thrust within the duct using a wheel or a snake type robot because it is hard to obtain an appropriate reaction force in a deformed pipe. Therefore, the pipe must be gripped stably even if it is flexible so that thrust can be generated to run the cleaning robot through the pipe. In this paper, we modeled a cleaning robot that uses peristaltic motion running through a flexible duct with an inner diameter of 50 mm. Then, the validity of the model was verified by experiment. Finally, a cleaning experiment was conducted and the cleaning rate was 98.7 %.