Soft robotics has recently become a popular topic owing to its advantages over conventional rigid robotics. 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.

Soft growing robots, a new soft mobile robot, have recently attracted considerable interest. There are many soft growing robots, some of which have irreversible growing and bending motion mechanisms. For such robots, path planning methods that provide information on bending timing improve operation efficiency. Although various path planning methods have already been developed, they cannot be applied to our growing robot that uses a heat welding mechanism because it has a constraint that all bending angles are the constant value. This letter proposes a novel path planning method with constant bending angle constraint. The proposed algorithm was developed based on the rapidly-exploring random tree star (RRT ^* ) algorithm. The method incorporates an algorithm for reducing unnecessary nodes from obtained paths keeping bending angles constant and improving path optimality. We confirmed that the proposed method generates paths whose bending angles are constant. In addition, we experimented with moving our robot along the path in the field with some obstacles. The result showed that the proposed method enabled the robot to reach to target place, avoiding obstacles. The proposed method improves the operating efficiency of our soft growing robot.

This letter presents a novel soft climbing robot characterized by its light weight, flexibility, and the ability to adjust the locomotion distance by extendable arms. The robot has inflatable gripper and arms. These are controlled only by a pneumatic system. The weight of the robot is 858 g, the maximum length of the extendable arm is 740 mm, and the contraction ratio (distance between the minimum length and the maximum length/maximum length) is 88%. We evaluated its ability of locomotion by experiments in which the robot moved on a field structure consisting of pipes. The robot successfully moved continuously, and hence the effectiveness of proposed climbing method was verified.

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.

Various types of extendable and contractible soft actuators have been developed by utilizing their strength, lightweight, and flexibility. Most soft actuators focus on either the extending or contracting motion. In this study, we aim to achieve both motions in a single actuator. We propose a novel lightweight soft extendible actuator driven solely by air. Driven in low pressure, this actuator exhibits a high contraction rate and extends without the aid of any external force, such as gravity, and contracts under tension loads. The actuator weighed 191 g and realized a maximum length of 980 mm at extension and contraction rates of 870%. We experimentally evaluated the performance of the actuator with respect to the operating parameters and internal pressure during the extending motion and with respect to the exhaust air volume and contraction rate during the contracting motion under the application of a contraction force. The results indicate that the actuation principle can effectively prevent buckling. Additionally, an efficient contracting motion can be achieved as the contraction force relies on the exhaust volume and length.

Soft growing robots are a new type of soft mobile robots that can move in environments that are challenging for conventional wheeled robots and interact with the surrounding environment. The bodies of existing soft growing robots are constructed from one tube without branches, which limits their movement and interaction capability in an environment. However, adding branches would allow the robots to explore multiple areas simultaneously while also providing support. Therefore, a novel mechanism that creates branches on demand on a soft growing robot body is proposed in this letter. This mechanism uses heat cutting to create a hole in the trunk tube to allow branch tubes to pass through the trunk. Further, we developed a branching model to estimate the time required under different inner pressure values and with different diameter branch tubes. The experimental results agreed with the proposed branching model, and we confirmed that the time for branching can be estimated from the model. We also demonstrated that the proposed mechanism could create a branch anywhere on the trunk tube using the carrying mechanism that moves on the tube. We believe that this branching mechanism can be used with various soft growing robots to enhance their operation.