This paper proposes an in-pipe robot capable of creating route maps for narrow pipelines with inner diameters of both 3-in and 4-in. Pipe route-drawing often relies on external sensors, such as cameras and light detection and ranging (LiDAR). However, due to lighting, dirt, and spatial constraints within the pipeline, miniaturization has been challenging. Therefore, our method uses only internal sensors, such as a tiny inertia measurement unit (IMU), for robot posture acquisition and an encoder for distance measurement. Furthermore, a sensor-less joint torque control system was also implemented by using a specially designed printed circuit board with motor current regulation, allowing the robot to traverse the pipeline while suppressing excessive torque generation and slippage. The experiments to verify the performance of our route-drawing method were conducted on two types of pipelines with 3-in and 4-in inner diameters. It was revealed that the mean absolute error in the length of the straight sections was within 3% for all pipes, that in the rotational angle of the bent pipes was within 2 deg, and that in the direction of the straight pipes was within 2 deg.

This study introduces an agile robotic penguin featuring a pair of 2-degrees of freedom (DoF) wing mechanisms. Each wing can independently control flapping and feathering motions with two in-house submersible geared servomotors through a differential gear mechanism. Notably, our mechanism allows unrestricted feathering beyond 360°. Since feathering directly changes the wing’s angle of attack (AoA), the hydrodynamic forces can be significantly adjusted to achieve agile maneuvers. This paper demonstrates various maneuvers, including rapid acceleration, hard braking, rolling, pitching, and yawing, achieved solely by changing the feathering motion of both wings. Our robotic penguin reached a maximum forward speed of 1.8 m/s, comparable to the foraging speed of real penguins. The average roll, pitch, and yaw rates were 363°/s, 75°/s, and 92°/s, respectively. This robot serves as a model for the biological study of maneuverability in real penguins and the engineering exploration of bioinspired agile underwater robots.

This paper presents a method of drawing pipeline routes using a sensing unit with a rotary encoder and IMU (Inertial Measurement Unit), which is towed by a self-propelled in-pipe inspection robot. However, the IMU information generally contains integration errors, making it difficult to draw accurate pipeline routes. In this study, we propose a method combining gradient descent using a gyroscopic sensor and an accelerometer, and the correction of the route based on the standard information of the pipe. First, the method of identifying the start point, end point, direction of straight pipes, and bending direction of curved pipes is explained. Then, an experiment is conducted using the developed robot system on a 11.6-meter-long pipeline course that includes nine curved pipes and horizontal and vertical straight pipes. Consequently, the mean absolute error of the route dimension was reduced to 2.74 %.

The paper reports the performance verification of vertical bend and T-branch travels of an articulated wheeled in-pipe inspection robot. The robot is composed of only a single active compliant middle joint, two passive compliant joints, three drive wheels, and two roll wheels. The passage of the bend pipe is achieved only by the joint torque control, while the T-branch travel is achieved by controlling both joint angle and torque. Instead of using a torque sensor, a polyurethane-based series elastic actuator (SEA) is installed in the middle joint. In this paper, the travel performances of our developed in-pipe robot were tested on bend pipes and 10 types of T-branch with different gravity directions. From the experiments, in all cases, the effectiveness of the bend and T-branch travels performance was confirmed.

This paper presents a wheeled V-shaped in-pipe robot in which the two outputs of the wheel shaft and roll joint are driven solely by a single actuator input. This underactuation is generated by a simple miter gear mechanism. Generally, to control two movements easily, one of the outputs of the underactuated mechanism is constrained by the resilience force of springs or by the friction force. However, this complicates the control of each output. In this study, a one-way clutch is installed to completely constrain one of the outputs (wheel movement). By using this clutch, the proposed mechanism enables a hemispherical wheel to switch between pitch and roll rotations by selecting the drive direction of a single motor. The one-way clutch constrains the wheels to rotate in only one direction. To take advantage of this constraint, the robot changes its direction of movement between forward and backward by using the rolling movement of the robot. After describing the configuration of the proposed robot and a roll-angle model of the robot, experiments are conducted in straight pipes, bending pipes, and an out-of-plane double elbow.

AIRo-5.1 an in-pipe inspection robot comprised of two passive compliant joints and a single active compliant joint that is driven by a series elastic actuator (SEA) is presented in the course of this study. As an aid in pipeline maintenance, AIRo-5.1 controls joint angles and the torque of middle joints, to enable them to adapt to bend, branch, vertical pipes, and slippery surfaces. To sense the joint torques, an improved durable polyurethane rubber spring was installed. To smoothly pass through T-branches, the angle trajectory of middle joints was calculated based on the pipe geometry and thus, was interpolated using a cosine curve. Experiments to verify robot performance in bent and T-branch pipes, its joint angle and torque control was conducted.

This study presents an in-pipe inspection robot module, called AIRo-2.3s. This robot module can control its joint angle and torque and adapt to any directed bent pipe regardless of its orientation. Stretching the drive wheels against the inner wall of pipes is essential for adapting robots to be used in vertical pipes and slippery inner surfaces. To achieve this, a series elastic actuator (SEA) with a high reduction system and a polyurethane rubber is installed to sense the joint torque. More than 100 N constant traction force and a wide range of adaptive inner diameters (4 to 6 in.) are achieved despite the short body length, a minimum number of the drive wheels, and a simple joint of 1 degree of freedom. Experiments to verify the performance in bent pipes are conducted after the robot module configuration is described.

This study presents a differential elastic joint for use in multi-linked pipeline inspection robots. Active joints to stretch against the pipe wall are essential for adapting robots to use in vertical pipes and slippery inner surfaces where a large traction force is required. Series elastic actuators with a high reduction system have typically been used to sense force/torque in such applications. However, compactness, power, and bi-directional series elasticity are required to conduct in-pipe inspections. In this study, we propose an active joint using a differential elastic actuator with a rubber spring for decreasing the size and increasing the stiffness of the joint. After describing the configuration of the differential elastic actuator that is suitable for our robot and the design theory of the rubber spring cross-section, we conducted experiments to verify its torque property.

In this paper, we present a multi-link articulated wheeled in-pipe robot that can drive the wheel and roll joint by using only a single actuator installed in each link. The proposed mechanism enables the robot to move forward or backward and helically in pipes owing to rotation of the drive wheel and twisting of the body. These two movements are generated by a miter-geared differential mechanism installed in each joint, and the magnitudes of these movements depend on the load applied to the wheels and roll joints. However, controlling of two outputs independently and aligning the rotation of the roll joints as desired are extremely challenging. Therefore, in this study, we switch those two movements by driving the rear wheels and the front wheels of the robot alternately. In addition, a stopper is used to constrain the roll joint movement. By calculating the angle of elevation of the robot's helical movement in the pipe by using a kinematic model, we can design a stopper to precisely adjust the roll angle. We verified that the robot can twist using the differential mechanism, and we validated experimentally the effectiveness of the stopper.

This paper presents an anisotropic shadow-based operation assistant method for a multilink-articulated wheeled pipeline-inspection robot by using a single illuminator and camera. By displacing the position of the illuminator relative to that of the head camera, a crescent-shaped shadow appears in the images captured in a bent pipe. The size, position, and orientation of the shadow depend on the robot's orientation around the pipe axis, and the shadow disappears in a certain robot's orientation (anisotropic shadow). Generally, as for shadow based navigation systems, disappearances of the shadow should be avoided because the robot loses its way. However, our previously developed robot (AIRo-2) adapts to a bent pipe without any control when the robot's orientation and the pathway direction of the bent pipe are aligned. By aligning those two specific orientations, we propose operation assistant system to pass through winding pipes. In this paper, the shadow region is extracted using two types of image binarization. The proposed system was experimentally verified in pipelines including seven bent pipes by applying the pathway direction of the bent pipe (obtained from the shadow) to the rolling movement of the robot.

This paper presents a multilink-articulated robot with omni and hemispherical wheels (AIRo-II) for inspecting and exploring winding pipes. To quickly adapt to winding pipes, holonomic rolling movement without moving forward and backward is more useful. However, this requires the replacement of driving actuators with rolling actuators at the expense of the driving force. In this paper, we investigate the possibility of high maneuverability of multilink-articulated robots in winding pipes by using less actuators and by designing spring joints. We further validate this by experimental verification.

In this paper, we present a new in-pipe robot with independent underactuated parallelogram crawler modules, which can automatically overcome inner obstacles in the pipes. The parallelogram crawler modules are adopted to maintain the anterior-posterior symmetry of forward and backward movements, and a simple differential mechanism based on a pair of spur gears is installed to provide underactuated mechanisms. A central base unit connects each crawler module through foldable pantograph mechanisms. To verify the basic behavior of this robot, primary experiments in pipes with different diameters and at partial steps were conducted.

This paper presents a new suction cup with a disc spring for exiting adsorption mechanisms (for example, wall-climbing robots). The center of the suction cup can be pulled up manually through the use of buckling of the disc spring. When deformation of the disc spring reaches a certain balance point, it can sufficiently generate adsorption force. However, with time, the adsorption force will gradually decrease because of air inflow into the suction cup. Then, the spring can be automatically pulled up again to next balance point according to the air inflow. Repeating this process enables the adsorption for a long duration. By pushing back the disc spring to the original position manually, the suction cup is easily detached from the wall. This proposed suction cup can achieve long adsorption, easy attachment and detachment, and energy saving. In this paper, analysis of the adsorption force, design of the suction cup, and experiment of the prototype are conducted.