Soft robotics has recently become a popular topic owing to its advantages over conventional rigid robotics. In this article, we introduce a soft robot that can grow with its own structure; its main components include an inflatable tube for its body and a tip with an expansion mechanism. The tube is made of conventional laminated film. It leads the robot to improved applicability. The robot can grow along the horizontal and vertical directions, and it can bend around yaw and pitch axis. To achieve this, a mechanism feeds air into the inflatable tube for growing the structure, and another heat welding mechanism allows producing bending points where necessary. The experimental results confirm that the proposed robot can grow in mid-air and bend around the yaw axis with varying bending radii. Further, the robot can climb a wall and displace an upper surface by pitch-axis bending. The designed bending structures are very stable because of heat welding; the growing and climbing capabilities depend on the inner pressure of the tube, and these capabilities allow the robot to select various shapes and move seamlessly in various environments.

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Soft growing robots have recently attracted considerable interest. They are expected to operate in complicated environments leveraging their flexibility and adaptability. However, some of them are unable to maintain their bending shape without contact with an object, and some of their mechanisms are complex. In this article, we propose a novel heat welding mechanism for pitch-up motion without any support. The proposed robot uses a gusset folded tube and welds its gusset parts. The welded tube is bent, and the robot performs a pitch-up motion. In addition, we experimentally investigate the characteristics of welded bending tubes and develop a stiffness model and bending angle model. The results demonstrate that they depend on the tube diameter, weld shape, and inner pressure. We conducted experiments to evaluate the performance of the robot and confirmed that the maximum bending moment based on which the robot can maintain its bending shape increases under a higher inner pressure, and a large bending angle is obtained by continuous bending. Further, we confirmed that proposed models can adequately simulate the pitch-up motion of the robot. The proposed mechanism enables the robot to perform novel pitch-up motion and expands the application of growing robots.

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