Motoyasu TANAKA (田中 基康)

In this paper, we propose a control method for the snake robot to adapt its body shape to the rope tension while climbing a rope, which is a flexible environment, in response to the joints’ current. The frictional force and the robot joint load vary depending on the amount of rope tension. A large tension may overload the robot joints, but a small tension may cause the robot slip and fall. Therefore, it is important for the robot to be able to change its body shape and adapt appropriately to the tension in rope climbing. In order to achieve this, we focused on the fact that joint loads and motor current values are related and devised a control system to change the robot’s body shape according to the motor current values. The concept is to change the robot’s body shape in order to obtain the maximum twisting angle at a constant current value. It should be noted that this control cannot guarantee that the robot will not slip and fall, but it can avoid excessive joint loading. The efficacy of this control for tension adaptation was validated through experiment.

This study presents an autonomous inspection system for underground pits using an articulated mobile robot. The underground pit is composed of several rooms surrounded by concrete connected to each other by winding pipes. Based on an action list created in advance and environmental maps, the robot autonomously inspects the underground pit by switching between three actions: planar motion, winding pipe passing motion, and image capturing. In planar motion, the robot moves around the room while avoiding obstacles and crosses ditches through distinctive behaviors, switching the allocation of the grounded/ungrounded wheels. In the winding pipe-passing motion, the target path is autonomously generated based on the parameters of the winding pipe. Laboratory and field tests were conducted to demonstrate the effectiveness of the proposed system.

This study proposes a novel approach for a snake robot traversing an environment composed of two planes, one fixed and the other varying in inclination. Instead of adapting to the environment, the robot propels itself by deliberately changing the environment into a form that facilitates mobility. Assuming that the robot straddles two planes, the inclination of the planes is changed by controlling the motion of the part that straddles them. The proposed method changes the inclination only through movement of the robot, which straddles the planes. Therefore, other body parts can be used in conjunction with other motions using conventional methods. The effectiveness of the proposed method and its limitations were verified through physical simulations. The simulation results confirmed that the snake robot can modify the inclination of the plane if its posture is suitable for modifying the environment.

This paper proposes a hanging motion for snake robots by utilizing half-hitch knot tying, which is a type of rope work. The proposed method prevents a robot from falling off a pipe by tying it to the pipe. In addition, the robot can hang from a pipe by grasping it using the knotting part. The parts other than the knotting part can be operated arbitrarily and applied to various actions. We propose a transporting motion as one of the applications of the hanging motion. The effectiveness of the proposed motion was experimentally verified using an actual robot.

A snake robot can form various shapes by fitting to an arbitrary continuous curve thanks to its numerous degrees of freedom. When traversing an unknown complex environment, a snake robot may need to perform local shape transformation to avoid obstacles or perform specific tasks. In this study, we present a local shape transformation control method for expanding the mobility of a snake robot. The proposed control method lifts a local part of the robot away from the target continuous curve while the leading part and the trailing part shift accordingly to remain fitted to the continuous curve without twisting. The proposed local shape transformation is realized by changing the approximation range on the continuous curve without changing the shape of the continuous curve. Simulations were conducted to evaluate the effectiveness of the local hump-shaped transformation control on various types of continuous curves. We also evaluated the proposed control method by comparing it with other local shape transformation control methods through simulations. Additionally, we propose two examples of applications which are the recovery from a stuck state and recovery from joint failure. Experiments were conducted to verify the effectiveness of the proposed control method.

This paper proposes a novel motion design for a snake robot to move freely in a space between two adjacent walls. Snake robots are expected to be useful in several difficult environments because of their high degrees of freedom. Particularly, they are suitable for use in narrow spaces. However, freely moving in narrow spaces, such as spaces between two adjacent walls, remains an open problem. In this study, inspired by helical rolling motion, which is used to move on a pipe, we propose a novel motion method that enables a snake robot to move freely in a narrow space between two adjacent walls. The motion and model are validated using physical simulations.