It is a well-known fact that Japan saw an annual average economic growth rate of over 10% from around 1955 to around 1973, its so-called “high-economic-growth period.” Japan’s rate was two to four times higher than that of Europe or the United States. During this period, Japan’s infrastructure (roads, bridges, tunnels, etc.) was rapidly developed nationwide, bringing Japan’s national average road pavement ratio in 2017 to over 80%, one of the highest rates in the world. Such rapid infrastructure development has made all of Japan a comfortable place to live. However, as Japan’s infrastructure is now becoming increasingly deteriorated, the structures nationwide must be inspected for soundness and should be repaired or rebuilt if any defects are found. As these structures are highly developed, the number of structures to be inspected becomes so numerous that the human-based inspection cannot keep up.

This situation has led to growing calls for artifact inspection systems that carry out inspection work more efficiently, and the Cross-ministerial Strategic Innovation Promotion Program (SIP) was established, one of which is “Infrastructure Maintenance, Renovation and Management,” with Yozo Fujino as Program Director (SIP Infrastructure), having been implemented for five years since fiscal year 2014.

This Special Issue on Infrastructure Maintenance and Inspection Robotics has collected papers that propose a broad range of infrastructure maintenance/renovation/management technologies, especially those developed by SIP Infrastructure, in order to contribute to the further development of the field of infrastructure maintenance and inspection technologies.

Construction of infrastructures, such as bridges and tunnels, has increased significantly in Japan in the past 50 years. Most of the civil infrastructure is now aging rapidly. Basic infrastructure maintenance and management require proper repairing and reinforcement, for which periodic inspections are indispensable. Inspection of civil infrastructure, however, requires a large amount of workforce for traffic regulation and accessing difficult-to-reach locations. Occupational safety is also an important issue that cannot be ignored. Furthermore, technologies related to emergency responses after the occurrence of natural disasters are important, especially with the increasing number of natural disasters recently. Executing a safe and quick disaster response action is very challenging. To meet the above problems, “Infrastructure Maintenance, Renovation and Management” was established in the Cross-ministerial Strategic Innovation Promotion Program (SIP). Research and development programs for infrastructure management systems using new technologies had been conducted since 2014. In this paper, the research and development programs related to robotic technologies are described. Specifically, robotic technologies for bridge inspection, tunnel inspection, and disaster responses are introduced. In addition, the scheme of the SIP regional bases that facilitates the availability of the developed technologies to local governments is also introduced.

To advance the automated inspection and maintenance of the inner wall of tunnels, an advanced inspection system aimed at regulating traffic was developed. In this inspection system, a guide frame was installed along the tunnel ceiling wall that is above the protection frame built over the road and resembles a gantry crane. The inspection device was fitted with an inspection guide frame (IGF), which stabilized its movement and improved its accuracy. However, as this protection frame moves along the tunnel, the guide frame should have the capacity to avoid convex obstacles such as the duct fan, the lamp and road traffic signs within the tunnel. Therefore, the entire inspection guide frame is made of variable geometry truss (VGT), which makes it possible to suitably alter the shape of the guide frame whenever necessary and pass it through the tunnel. To enable the guide frame adapt to any shape, the inverse analysis method and mathematical interpolation method were applied. The orientation of each frame was reversely analyzed according to the shape of the obstacle measured using the laser range finder (LRF), and the frame’s actuator was controlled simultaneously. We investigated the construction of a system that can perform a series of tasks such as searching for obstacles and positioning, frame shape simulation, frame shape change, inspection of the device and movement. By applying spline interpolation, we managed to practically determine the shape of the guide frame that would avoid obstacles.

Users of bridges and tunnels are generally concerned about the aging of these structures. Periodic inspections are necessary to keep old bridges and tunnels healthy. Inspection engineers must approach the inspection points as close as possible by mobile elevating of the work platform for close visual inspection of lining concrete. The inspection of a road tunnel particularly requires traffic regulation. Furthermore, it takes much time to perform visual inspection and hammering test for the vast area. Moreover, the inspection results have variations by inspectors. We propose an “Inspection Vehicle” for inspection of tunnel lining concrete by a new technology for infrastructure maintenance. This study reports the finding on element technology of an inspection vehicle and applies a tunnel inspection test.

This paper presents a shadow-based operation assistant method for a pipeline-inspection robot using a variance value of the image histogram. By displacing the position of the head camera relative to that of the illuminator, 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. By applying the pathway direction of the bent pipe obtained from the image processing to the rolling movement, the robot can automatically adjust its roll-orientation. Experiments were conducted in four types of pipeline environments to verify the autonomous navigation. These include a complex winding pipeline, a long straight pipe, and pipelines with replicated dust and dirt.

This paper describes a method to increase both the cleaning performance and speed of a peristaltic duct-cleaning robot, besides the cleaning of a real house duct. Duct piping ventilation is an important component for safeguarding indoor human health. However, dust accumulates inside such ducts during long-term use of ventilation systems. This dust leads to the generation of bacteria, dispersal of which can cause serious human health problems. Therefore, it is necessary to clean such ducts. The ducts used in factories, for example, have a large cross-sectional area and so are easy to clean by conventional duct-cleaning methods. However, as housing ducts have a small cross-sectional area and many curves, they are difficult to clean via the passive method of inserting a cleaning tool through the duct ports. For this reason, the authors attempted to develop a method of duct cleaning using a robot that imitates the peristaltic movement of earthworms. Herein, the authors examine the type and mounting position of the cleaning brush that produces the optimum cleaning efficiency. From this, we confirmed the duct cleanability of the peristaltic robot.

Public infrastructures, such as tunnels and bridges, are important for our daily life and their increased deterioration causes concern. Culvert pipes are installed underground below roads, and their damage has an impact on the function and integrity of infrastructures. However, culvert pipes in closed and confined spaces are difficult to inspect, and their conditions are generally not evaluated. In this paper, we describe the findings of field experiments involving the inspection of the inside of culvert pipes via robotic systems.

In this paper, we show the development of a lifting system and frame body for an inspection robot targeting hanger ropes of a suspension bridge. Infrastructure now requires regular inspection and such robots are expected to be used in places where manual inspection is difficult. The problems associated with the lifting system for the hanger-rope inspection robot studied in this paper include a long lifting distance (up to 100 m), postural stability against the influence of wind, and risk of falling. To solve these problems, we propose a lifting system with an alternating rotation mechanism, which takes advantage of the lifting mechanism of a climbing doll. In this paper, we explain the design and control methods of the lifting mechanism and alternating rotation hoist to realize the proposed lifting system. For the moving frame body, we designed and made a mechanism and frame structure to maintain stability of its posture. Performing an operation test in our laboratory and in the field with the proposed system incorporated into an actual unit, we checked the action of the proposed mechanism. In particular, we could confirm in the field test that the postural stability necessary for shooting inspection images could be ensured in an environment with wind speed of 5 m/s and that ascending and descending motions could be successfully performed with the current output of the alternating rotation hoist, even in an environment with a mean wind speed of 10 m/s.

To automate nondestructive inspections for concrete walls by measuring their air permeability, we developed a wall climbing robot with suckers. It is configured to move by alternately moving the central body and the four leg tip suckers forward. The central sucker is a triple ring type, making it useful for climbing and measuring as well as acquiring the air permeability data in the depth direction. The leg tip suckers use a sponge material to ensure good sealing with the concrete wall and are double suckers when incorporated with bellows to generate power that sticks them fast, by pressing the bellows at the beginning of the fast-sticking process. The dual stage fast-sticking process first sucks by using the bellows only and then the whole sucker follows after the sponge parts are almost fast stuck. To automate the dual stage fast-sticking process, we developed two automatic switching systems: one switches relative to the distance between the sucker and the wall surface and the other, relative to the pressure in the bellows. We experimentally demonstrated that with both switching systems, when the sucker approaches a concrete wall with a weak force, the first stage fast-sticking process takes 1 s or lesser and the complete fast-sticking process, approximately 5 s. We also proved that the developed wall climbing robot incorporating the above-mentioned fast-sticking mechanism can climb a concrete wall at approximately 440 mm/min to acquire the concrete’s nondestructive air permeability test data.

This study aims to develop a clinging device for structural inspection robots, which are expected to be used to reduce the cost of inspection of aging civil infrastructure and industrial structures. In a previous study, an electro-permanent magnet (EPM)-based clinging device that could electrically turn on and off the magnetic adhesive force against steel structures was proposed. In this study, a more versatile design of the clinging device was firstly presented, and a considerable difficulty regarding the activation process of the EPM which might impair the reliability of the clinging device was stated based on mathematical modeling and experiments. The concept of a two-step activation process was then presented to overcome the stated difficulty, and its implementation using a limit switch-based contact sensor was successfully demonstrated through collision tests. Furthermore, sensorless realization of contact detection by measuring the induced voltage across the coil of the EPM was proposed, and its feasibility was validated.

We developed a bridge inspection support robot system that uses a two-wheeled multicopter and 3D modeling technology. Our system is divided into three main parts: 1) a two-wheeled multicopter to capture close-up images of the inspection target, 2) damage extraction using 3D modeling technology, and 3) a 3D model-based bridge maintenance system that stores inspection information linked with the Industry Foundation Classes (IFC) 3D product model. An inspector can use this system to visually inspect the overall structure and accurately detect hairline cracks.

Recently, with the deterioration of bridge facilities, demand has arisen for a method to inspect many bridges efficiently. One proposed bridge inspection method involves observation and inspection of cracks on undersides of bridges using a video camera mounted on an unmanned aerial vehicle (UAV) that flies under the bridges. There is an option to have a pilot operate the UAV, but it is desirable to have the UAV fly autonomously when efficiency of inspection is considered. Though there is a method using GPS for autonomous flight control of UAVs, there are many cases in which GPS cannot be utilized under bridges, and a new method is required for autonomous flight control in such places. The authors have already shown that autonomous flight control of UAVs can be achieved within the range of a monocular camera image by measuring the position of a UAV using camera images. However, since the flight range is bounded by the monocular camera image, it is necessary to move the camera position to fly the UAV autonomously in a wider space. In this paper, it is shown that a UAV can achieve autonomous flight control in wider spaces by constructing a single coordinate system for a combination of two camera images. In addition, considering that various measuring instruments might be mounted on a UAV, an adaptive control method capable of obtaining good control performance without changing the design parameters of the controllers should be applied. This method is useful for maintaining control performance when the total weight of the UAV changes. To show the effectiveness of our proposed method, we give an appropriate practical flight target orbit and present its experimental results.

This paper describes the development of a hanger-rope inspection robot for suspension bridges. The inspection robot inspects the hanger rope by going up and down the rope installed vertically downward from the main cable of a suspension bridge. The going-up-and-down mechanism of the robot consists of a drive roller driven by a motor and a non-excitation electromagnetic brake, and the robot can safely descend after climbing the rope at high speed. The developed robot is small in size and light in weight, and an inspection worker can easily install the robot on the rope. In addition, the robot can be wirelessly controlled with ease from the controller. First, this paper describes the hanger-rope inspection strategy of the suspension bridge. Then, the developed prototype 2 robot is introduced. Next, the result of the hanger-rope inspection in an actual suspension bridge and the problems are clearly revealed by experiment. Finally, the newly developed prototype 3 robot is introduced, and the result of the going-up-and-down experiment is described.

The tiles that are used to protect the exterior of a building may separate from the concrete substrate and fall off as they age. To prevent accidents, a tiled wall can be inspected using various methods. In this study, nondestructive inspection (NDI) with microwave electromagnetic waves (EMWs) is used for detecting tile separation, and the chance of detecting the separation by this method is discussed in this paper. Here, the inspection apparatus is used to detect voids in concrete, including voids that simulate tile separation. An antenna attached to the apparatus transmits and receives microwaves to obtain a reflected intensity from the concrete. In addition, the distribution of reflected intensity is obtained using a proposed scanning method, multi-layered scanning. This involves several scans along the concrete surface at different antenna-to-surface distances. Typically, EMWs have to be analyzed with an expensive network analyzer in the time or frequency domain. However, we demonstrate that voids are detected from the obtained distribution of the reflected intensity of EMWs measured by a simple device without a network analyzer. The proposed method of NDI with EMWs is cheaper and simpler than conventional inspection methods.

In this study, a novel approach was developed to achieve fast bipedal walking by using an actively controlled wobbling mass. Bipedal robots capable of achieving energy efficient limit cycle walking have been developed, and researchers have studied methods to increase their walking speed. When humans walk, their arm swinging is coordinated with the walking phases, generating a regular symmetrical motion about the torso. The bipedal robots with a wobbling mass in the torso mimicked the arm swinging by the proposed control method. We demonstrated that the proposed method is capable of increasing the bipedal walking speed.

The objective of this study is to extend the application of the spray-coated tactile sensor, ScoTacS, which is being developed by the authors and can be constructed simply by “coating” with a spray gun, from one dimension to two dimensions, and further to configure it into various shapes such as a ring. This sensor is constructed by coating three layers-conductive, piezoelectric, and resistive films-in sequence. It is based on a unique principle by which the contact position is detected from the delay time, i.e., the time difference between the arrivals of peaks in the output signals. As the delay time varies with the contact position, it can be used to estimate the contact position. In this paper, after analyzing the characteristics of one-dimensional sensors, such as linear and ring sensors, we present the equivalent circuit models and experimental results of a two-dimensional sensor fully coated on a cylinder.

This paper describes the development of a three-degrees-of-freedom flapping-wing robot with a variable-amplitude link mechanism for controlling the lift and thrust forces acting on it. The variable-amplitude link mechanism comprises a lever-crank mechanism driven by a brushless DC motor and a linear actuator to control the amplitude of the flapping angle. The robot also comprises two DC motors with reduction gears for feathering and lead-lag motion. In our experiments, the measurement of force-torque revealed the effects of the motion of each wing. We found that the flapping-amplitude difference between the left and right wings causes a roll and yaw moment.

In this paper, we discuss the pattern formation of objects that can be stacked and transported by distributed autonomous agents. Inspired by the social behavior of termite colonies, which often build elaborate three-dimensional structures (nest towers), this paper explores the mechanism of termite-like agents through a computational and minimalistic approach. We introduce a cellular automata model (i.e., spatially discretized) for the agents and the objects they can transport, where each agent follows a “rule” determined by the assignment of fundamental actions (move/ load/ unload) based on the state of its neighboring cells. To evaluate the resulting patterns from the viewpoint of structural complexity and agent effort, we classify the patterns using the Kolmogorov dimension and higher-order local autocorrelation, two well-known statistical techniques in image processing. We find that the Kolmogorov dimension provides a good metric for the structural complexity of a pattern, whereas the higher-order local autocorrelation is an effective means of identifying particular local patterns.

In recent years, CanSats have become a popular choice in simulated satellite contests. Among CanSat contests, the ARLISS project is the one that uses rockets to launch the CanSat into the sky. ARLISS provides rockets to launch CanSats, which reach an altitude of ∼4,000 m and then drop the rover to the ground using a parachute. However, the rovers of several teams cannot withstand the large acceleration applied during the launch, which damage and make them non-operational. The acceleration applied to the rocket during the launch was measured by multiple teams previously; however, because the CanSat is a small-embedded device, an acceleration sensor with a wide measurement range and a high sampling frequency could not be used. In this study, we measure the acceleration applied to the rover from the launch till it drops on the ground using an acceleration sensor with a wider measurement range, and by acquiring data at a higher sampling frequency than before. The acceleration is found to be larger than that in the conventional measurement when the rocket is launched and it drops to the ground. Further, the descriptions of the technical details of the rover structure that can withstand these impacts, perform accurate measurements, and operate without breakage in ARLISS are provided.

A new laser microscope is developed to obtain depth-direction birefringence information of optically anisotropic samples, which cannot be obtained by a conventional polarization microscope. As a result, birefringence tomographic images are now available and the method should be helpful for sample evaluations.