The decommissioning of the Fukushima Daiichi Nuclear Power Plant, the plant affected by the Great East Japan Earthquake, will continue for a long time to come, but few young people are willing to take on the challenge because they tend to have the impression that decommissioning work is a post-accident cleanup. However, decommissioning is the most important issue for Fukushima and is of global importance.

Therefore, the National Institute of Technology, Fukushima College (Fukushima KOSEN), which is located closest to the Fukushima Daiichi Nuclear Power Plant, established a council of cooperation and started the Creative Robot Contest for Decommissioning in cooperation with other National Institute of Technologies (KOSEN) to increase the awareness and interest in decommissioning among the young.

The robot contest, themed on issues related to the decommissioning of the Fukushima Daiichi Nuclear Power Plant, has been held annually since 2016 for students of KOSEN across Japan, and the 7th Creative Robot Contest for Decommissioning is scheduled to be held in December 2022.

Although the ideas and robots developed by KOSEN students from all over Japan to solve the problems involved in the decommissioning will not directly contribute to future decommissioning work, the ideas and technologies learned can be used in other fields, and the participating students are expected to be active in a wide range of fields as well.

This special issue contains review papers of the Creative Robot Contest for Decommissioning, development reports, and research papers on the robots developed. A total of eight papers are included: two review papers, two research papers, and four development reports on decommissioning robots designed by students.

At the same time, we hope that young people in Japan and abroad will also become interested in the robots introduced in this special issue, and that the decommissioning work of Fukushima Daiichi Nuclear Power Plant will proceed safely and securely by combining the wisdom of the whole world.

This paper’s theme “Creative Robot Contest for Decommissioning (hereinafter, this Creative Robot Contest)” may be called a contest that would never have been planned in the absence of the Great East Japan Earthquake on March 11, 2011 and the core meltdown accident at Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company. When it was decided to decommission the nuclear reactors, their decommissioning was immediately put in hand, which, however, met with a high barrier of high radiation doses unconquerable even by the modern science and technologies. In order to advance the stagnating decommissioning work and in hopes of some creative breakthrough ideas from KOSEN students, this Robot Contest, first held in 2016, has been held by KOSEN teams who have shown their willingness to participate in it as a venue useful to address any difficulties they will face in the real world or as teaching material for them to consider social problems. This Robot Contest, sponsored by the Japan Atomic Energy Agency and the Council of Technical Colleges for Human Resource Development for Decommissioning, is planned and managed by the Executive Committee of Creative Robot Contest for Decommissioning (hereinafter, the Executive Committee) with its secretariat at National Institute of Technology, Fukushima College (hereinafter, Fukushima KOSEN) in Fukushima Prefecture where Fukushima Daiichi Nuclear Power Plant is located. In this paper, teachers at Osaka Metropolitan University College of Technology (hereinafter, Osaka Metropolitan University KOSEN) and at Nara National College of Technology, Nara College (hereinafter, Nara KOSEN), whose respective teams have participated in this Robot Contest every year from the first one, and teachers at Fukushima KOSEN who organize and manage the executive committee describe their own views on this Robot Contest based on their viewpoints as KOSEN educators. In the first half, this paper reviews this Robot Contest and outlines the robots of Osaka Metropolitan University KOSEN which participated in it in FY2016 and FY2017 and of Nara KOSEN which did in FY2016. In the latter half, this paper describes the views of the KOSEN teachers who educate engineers in the framework of robot contests from the viewpoints of the teachers who have instructed the teams of Osaka Metropolitan University KOSEN and Nara KOSEN who have participated in this Robot Contest up to the sixth one and who have held this Robot Contest.

We designed and fabricated robots with various mechanisms to solve the problems set in the Creative Robot Contest for Decommissioning. Robots with various mechanisms were designed and manufactured to solve the problems set by the Creative Robot Contest for Decommissioning. More specifically, a mechanism that can climb up the stairs robustly was realized by attaching claws to the crawlers to solve the problem of climbing up a steep staircase while carrying a heavy load. For the task of retrieving simulated fuel debris from a high location, we developed a mechanism to raise and lower the robot and a mechanism to retrieve simulated fuel debris without fail. Consequently, we realized the idea of robot technology required for decommissioning work and training human resources involved in decommissioning work.

This paper presents a robot developed for reconnaissance at a nuclear power plant that had an accident. When an accident occurs, such as the Fukushima Daiichi Nuclear Power Plant disaster, rubble is scattered on the premises, increasing the radiation dose. Consequently, it is nearly impossible for humans to enter the plant and assess the situation. Therefore, a robot that performs reconnaissance is required. In this study, we designed and fabricated a reconnaissance robot to be used in a nuclear power plant that has undergone an accident. The inaccessibility of the scattered on-site rubble and high radiation dose can be addressed by employing an airship-type design that does not use electronic devices.

The purpose of the Creative Robot Contest for Decommissioning is to raise students’ interest in decommissioning through robotics, contribute to the cultivation of students’ creativity, and develop not only their problem-solving ability but also their problem-finding ability. The contest assumes fuel debris removal from the lower part of the pedestal at the Fukushima Daiichi Nuclear Power Plant. This paper describes the activities of our college in the Creative Robot Contest for Decommissioning and the robot design to overcome the challenges of the 4th and 5th contests. Whereas the 4th contest was held on site, the 5th contest was held online. To evaluate the robot that we have developed, we prepared a mock-up of the contest field at our school and conducted a demonstration. In the 4th contest, our team was the only one among the participating teams to complete the task and won the award from the Ministry of Education, Culture, Sports, Science and Technology (MEXT). In the 5th contest, we won the award from the Governor of Fukushima prefecture. The educational effects of the Creative Robot Contest for Decommissioning were great. The students who participated in the contest became more interested in decommissioning and were able to develop problem-solving skills, the ability to study independently, schedule management, and so on.

A creative robot contest for decommissioning was held as part of human resources development for decommissioning of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Co., Inc. In the 5th creative robot contest for decommissioning, robots were developed for fuel-debris retrieval from the lower part of the pedestal. Fukushima KOSEN developed a robot consisting of a primary robot that moves to an access port on the platform while a secondary robot is stored inside the main body. The robot collects fuel debris by lowering the secondary robot 3.2 m downward. Fukushima KOSEN also developed a graphical user interface (GUI) to visually express the motion of the robot.

This is a report on the No.2 debris retrieval robot that has been developed. While unit 1 was a machine built to demonstrate basic ideas, such as the arm mechanism, the robot that was designed and manufactured this time was developed with an emphasis on its structure and the functions that can be used at the decommissioning site. Only the ideas of a crawler that can run through a thin pipe and a telescopic arm mechanism to access debris were carried over from unit 1; all other parts for debris retrieval robot No.2 were redesigned. The crawler was made from metal with significantly increased rigidity to improve the running performance of the robot. In addition, to improve maneuverability, an omnidirectional camera unit was installed. As the view of this camera is not limited to the direction of travel of the robot, it makes it possible for the operator to have a better grasp of situations that the robot may encounter. The debris collection mechanism was changed to a more reliable mechanism that is not affected by the shape of the debris. The arm expansion and contraction mechanisms were also changed to a more reliable structure.

In this paper, we describe a prototypical crawler vehicle developed for “Hairo Sozo Robocon,” i.e., the 4th creative robot contest for decommissioning conducted in 2019. The rules of this robot contest required a high turning ability on a flat floor and high mobility through the inner space of a pipe. In addition, the robot needed to salvage objects from a floor placed 3.2 meters underneath itself. We developed a multi-articulated tracked vehicle to provide high mobility in both contexts. The vehicle was equipped with a sensorless salvaging bucket inspired by a traditional sampler sounding weight.

This study developed a debris removal robot for the Fukushima Daiichi Nuclear Power Plant. The creative robot contest for decommissioning the nuclear reactors of the Fukushima Daiichi Nuclear Power Station is an annual competition based on problem-based learning. It aims to stimulate students’ interest in decommissioning nuclear reactors while simultaneously imparting problem-solving skills. The development of our debris removal robot started with this contest. The proposed robot can travel in a pipe, has a 3 m telescopic arm, and is equipped with a debris removal device known as a spiral catcher. This report provides an overview of this robot. We expect that complex robot development will be achieved by putting forth several ideas from various fields and fostering advanced problem-solving skills by encouraging students to address difficult tasks. Therefore, we successfully fostered the social implementation skills of students and developed a debris removal robot.

In this study, we demonstrate the avoidance of the “lost robot” situation when wireless communication is interrupted. In our proposed method, the mobile robot measures the unknown environmental shape using a laser range finder. The sensor data and additional information (thickness and material characteristics) of the real environment are combined into the line segment map. We found that the electric field strength can be simulated using the line segment map. Experimental results verify the effectiveness of our proposed method.

This paper presents a new hydraulic robotic leg for the humanoid hydraulic robot HYDROïD. The main parts of this leg are divided into two main parts; the knee subsystem and the ankle subsystem. The presented leg mechanism consists of 4 DOFs, all of which are operated using highly dynamic servo valves. The design of the leg is thoroughly presented and all of its parts are demonstrated. Moreover, the inverse kinematics for both sub-mechanisms are presented to be able to control the angular position of the leg joints. Also, a virtual dynamic model is introduced in which a position controller is applied to the model to regulate the actuating pistons, check the new structure, and analyze the position of the joints and their torques. To test the new leg experimentally, the new leg is assembled with the rest of the robot, and rapid prototyping software is used with a position controller. Experimental position tracking responses are introduced showing the validity of the new design and the implemented controller.

The monitoring and inspection of buildings, towers, and large chemical tanks can be dangerous and costly. A wall climbing multi-legged robot can climb and crouch to move the inspection probe closer to the wall surface. The typical wall-sticking crouching motion of multi-legged robot is unable to achieve this without an additional actuator at the foot base. This limits the design of a magnetic leg that is bulky enough to keep the robot stable during inspections. This paper provides the concept and implementation details of a coarse-to-fine inspection using a novel twisting motion to crouch the robot towards the steel surface without the need for an additional actuator at the magnetized foot joint. The center position error of this method is reported as less than 1 cm in radius. Additionally, this paper suggests using a linear motor to provide fine-tuning capability for the gentle touch of the ultrasonic inspection probe to the steel surface, protecting the probe from a direct crash during the coarse twisting crouch movement. Experiments have been conducted to confirm the validity of this concept on horizontally flat steel plates. The robot successfully crouch towards the surface and gently touch it with the ultrasonic probe. The results were reliable and comparable to manual inspection. For the 2 mm and 3 mm sample plates, the average measurement error compared to the ground truth from a vernier caliper was less than 2%, which is better than the measurement error (3%) of humans. The total time used was 2.475 seconds per inspection spot, which is 5.6 times faster compared to the expected time used to cover the same distance with a typical probe extension using a lead screw drive.

In modern manufacturing, the long-term handling of heavy objects is a main factor leading to muscle pain in the waist and lower back. Robots play an important role in reducing the burden on workers by compensating for the gravitational force. Energy-conserving passive mechanisms are commonly used in assistive robots because of their reliability and durability. One such mechanism is a spiral pulley and spring couple, which is a compact and reliable solution to provide a constant assistive force. A spiral pulley has a predesigned changing radius to balance the increasing restoring force of the spring as it extends. This allows the mechanism to exert a constant torque within the designed range. A crucial aspect of such a mechanism is the calculation of the shape of the spiral pulley. Accurate calculations enable the mechanism to provide a more optimal balancing ability. In this study, an innovative spiral pulley was designed by considering the cable tension variation along the cable attached to the pulley. The balancing performance of the proposed pulley was evaluated based on its accuracy in providing a balanced torque and an effective range. A comparative experiment using a conventional spiral pulley confirmed the effectiveness of the proposed pulley.

Carrying gripped objects at high speed can lead to gripping failure owing to loads applied to the gripper by its acceleration. When carrying an object at high speed, it is important to carry it with accelerations at which gripping is maintained. Previously proposed methods generated the shortest carrying trajectory for a predetermined trajectory path. In this study, focusing on the object-carrying trajectory and the hand attitude of the gripper, we propose a method to generate the shortest carrying trajectory by varying the state quantities. The proposed method considers the gripping force and the deformation of the gripper. During planning, we estimated the deformation volume of the gripper from its inputs and generated the shortest carrying trajectory with the allowable force and deformation values as constraints. Using the proposed method, we generated a trajectory capable of carrying objects in a shorter time (0.28 times) than in a straight-line trajectory and conducted experiments with a robot arm. The trajectory was generated while keeping the hand attitude unchanged. Through experiments, we have proved the effectiveness of keeping objects gripped on the generated shortest carrying trajectory. Compared with a success ratio of 0.47 in keeping objects gripped on the trajectory with the same time as the generated trajectory, the success ratio on the generated trajectory is as high as 1.0.

Research shows that it is practical for the normal human movement mechanism to assist the patients with stroke in robot-assisted gait rehabilitation. In passive training, the effect of rehabilitation training for patients can be improved by imitating normal human walking. To make the lower limb exoskeleton robot (LLER) move like a normal human, a tracking control scheme based on human gait data is proposed in this paper. The real human gait data is obtained from healthy subjects using a three-dimensional motion capture platform (3DMCP). Furthermore, the normal human motion characteristics are adopted to enhance the scientificity and effectiveness of assistant rehabilitation training using LLER. An adaptive radial basis function network (ARBFN) controller based on feed-forward control is presented to improve the trajectory tracking accuracy and tracking performance of the control system, where the ARBFN controller is deployed to predict the uncertain model parameters. The feed-forward controller based on the tracking errors is used to compensate for the input torque of LLER. The effectiveness of the presented control scheme is confirmed by simulation results based on experimental data.

Kumamoto Castle, consisting of towers and stone walls called Ishigaki, was severely damaged by the 2016 Kumamoto earthquake. As this castle has cultural significance in Japan, the damaged stone walls of the castle need to be promptly and accurately restored. In recent years, the utilization of 3D stone data has been studied to determine the position of collapsed stones precisely. The 3D stone data needs to be measured automatically in a short period of time for the efficient restoration of stone walls. To control the attitude of the stone, a small control moment gyro (CMG) device was proposed, and a robust controller with a model error compensator was applied to the CMG device. In this study, the measurement precision of a 3D model of stones using the CMG crane system was analyzed. The automatic measuring system consists of a CMG device and an elevator for a 3D scanner to reduce the load on workers. The scanning motion was planned automatically based on the shape and position of stones using depth sensors. The effectiveness of the proposed measuring system was evaluated using the accuracy and measurement time including the data correction time of the 3D modeling.

This study proposes a teleoperation system for assistive controlling of the movement of a mobile robot in a narrow path. The teleoperation system is created by combining data from real and virtual devices. In CoppeliaSim we applied the Braitenberg algorithm and the open motion planning library module (OMPL). The Braitenberg algorithm is a sensor-based automatic motion designed to aid the robot operator in maneuvering through the narrow path. While the OMPL is used to create a path for the operator to control the robot in narrow paths or intersections within a narrow path, the simulation uses a virtual proximity sensor to fulfill the Braitenberg algorithm requirement. With dynamic simulation a laser rangefinder obtains the environmental data and displays it on the simulation screen. The simulation scene is subjected to the virtual proximity sensor and the Braitenberg algorithm is applied to the simulation scene. Afterward, simulation scripts are written to incorporate the linear and angular velocities into a robot operating system for real-time robot control. The results showed that the system was capable of combining real-time dynamic simulation with the real world. Furthermore, the proposed system could aid the operator in narrow path environments while avoiding collision.

This paper analyzes an orthotic robot’s capability of changing the direction of motion as part of its gait process while it is being worn by a user. Exoskeletons and orthotic robots are presented, focusing on their capabilities regarding the implementing a turn of their lower limbs. The devices are analyzed, and a method is proposed, being safe for the user, which ensures the required change of the angular position of the user’s trunk, having performed a turn of the device. The smallest movement of each lower limb, which is necessary to enable a turn of the trunk in such a way that the turn can be performed by both lower limbs, is determined.

We propose a method for estimating the position and attitude of a mobile robot using a laser beam. To this end, we employ the real-world clicker, which was developed by the authors and consisted of a system that uses a TOF (time of flight) laser sensor mounted on a pan-tilt actuator to measure the three-dimensional position of the laser spot. A laser receiver was mounted on top of the mobile robot, and the position of the laser spot was measured by both the camera installed below the receiver and real-world clicker. We propose an algorithm that allows the estimation of the robot’s self-position and attitude while the robot is in motion by combining the use of odometry, and validate it through simulations and experiments.

A McKibben artificial muscle has strong asymmetric hysteresis characteristics, which depend on the load applied to the muscle. Thus, designing a controller for high-performance displacement is difficult. In a previous study, model predictive control with a servomechanism combining an inverse optimization algorithm with adaptive model matching, and a data-driven model-free adaptive control (MFAC) were introduced. As a result, a high tracking control performance was achieved in both control methods. However, model-based and data-driven approaches require a highly accurate mathematical model and a large number of design parameters, making them time-consuming, respectively. To solve these problems, in the present study, a controller design that requires no precise mathematical model and less design parameter tuning with trial and error was developed by combining conventional MFAC and virtual reference feedback tuning, which is a data-driven control method. Experimental results indicated that important design parameters, such as the initial pseudo-gradient vector and weighting factor, can be readily obtained. Compared with conventional MFAC, higher tracking control performance without overshoot was achieved in transient response, while the same level of control performance was maintained in steady-state response.

We previously reported a microelectromechanical system tactile sensor with elastomer-embedded microcantilevers. The sensor enabled the gripping control of soft objects by a robotic hand and acquisition of the object surface texture data. However, sensitivity improvement for more precise control and better texture information acquisition is desired. Here, the cantilever size and the sensor’s strain-gauge arrangement were redesigned, resulting in a sensor with significantly improved sensitivity. In addition, we report the sensitivity dependence on the cantilever size.