Motoyasu Tanaka

This letter introduces the gait motion of climbing ladder and net for a snake robot using partial caging. These gait motions only involve little contact between the snake robot and the environment, where the robot may slip down easily. A target body shape is proposed that incorporates partial caging into climbing motions to prevent the robot from slipping down. In addition, we propose the rolling motion in order to achieve better constraint to the environment. We performed experiments and demonstrated the effectiveness of our proposed method.

In this study, we designed an opposite helix gait for object transportation using a non-wheeled snake robot. The proposed gait enables straight motion, turning motion, and pivot turning motion, allowing the robot to transport objects without ground contact. The target shape of the proposed gait features helices facing each other in a distinctive configuration. An elliptical helix, with its height defined by arc length, was designed for turning motion. By utilizing the proposed shape and employing rolling motion, opposing forces can be generated. This enables pivot turning motion—a capability difficult for conventional snake robots—and allows for compensation of the relative position between the robot and the object through object position manipulation. We conducted actual robot experiments for each type of motion and object transportation to verify the effectiveness of the proposed method. In particular, the trajectories of straight, turning, and pivot turning motions were measured and compared with theoretical predictions.

In this study, we propose an analysis method to evaluate the relationship between the body shape and joint loads of a snake-like robot when a load is applied to the head. A snake-like robot is composed of multiple joints connected serially, and the load acting on each joint is difficult to analyze due to the redundancy of the snake robot. In addition, the snake-like robot has multiple contact points with the environment, which makes the problem ill-posed. Slope deflection method, which is a structural analysis method for continuous beams by accounting the flexural deformations, is used in this study to analyze the moments acting on each joint. The reaction force acting on each contact point with the environment is also analyzed. The effectiveness of the proposed analysis method was evaluated through simulations and experiments with multiple body shapes. The joint load is reduced by modifying the body shape, as demonstrated through simulations and experiments. This study shows that the joint load of the snake-like robot can be reduced by using a hump body shape.

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 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.

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.

This paper proposes a control method for semi-autonomous stair climbing using an articulated mobile robot. Stair-climbing motion is achieved by propagating a single backward wave along the body of the robot. The robot moves forward by shifting a part of the body lifted from the step (the elongating part) from front to back. Semi-autonomous stair climbing is accomplished by automatically determining when to shift the elongating part backward based on the relative position between the step and the robot. Furthermore, we developed an actual robot that can measure the relative position between itself and the environment to climb stairs semi-autonomously. The developed robot is equipped with several short-range sensors on the lower part of its body, which can measure the relative distance between the robot and the stair tread surface. The effectiveness of the proposed control method was verified by simulations using a physics simulator and by experiments with the developed 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.

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.