In this fourth of the “Special Issues on Real World Robot Challenge in Tsukuba,” we feature the control technology of autonomous robots. There is no guarantee that it will operate perfectly in a real-world environment even with the method already revealed. Participating robots in Tsukuba Challenge are required to carry out the assigned tasks under the prevailing weather conditions on the day of the events. Robots avoid oncoming pedestrians and obstacles in their path. In order to share the novel technology of the autonomous control method, this special issue presents a summary of the results of robots that participated in past Tsukuba Challenges.

It is only thanks to the ongoing efforts of the organizers of Tsukuba Challenge and the enthusiasm on the part of the participants that we are able to present an issue such as this, and we are truly thankful to them. We also wish to thank the authors who submitted papers and articles for this issue, as well as our reviewers.

Legged locomotion, including walking, running, turning, and jumping, strongly depends on the dynamics and biological characteristics of the body involved. Gait patterns and energy efficiency, for example, are known to be greatly affected by not only travel velocity and ground contact conditions but also by body configuration, such as joint stiffness and coordination, as well as foot sole shape. To understand legged locomotion principles, we must clarify how the body’s dynamic and biological characteristics affect locomotion. Effort must also be made to incorporate these characteristics inventively to improve locomotion performance, such as robustness, adaptability, and efficiency, which further refine the legged locomotion. This special issue on “Dynamically and Biologically Inspired Legged Locomotion,” studies on legged locomotion based on dynamic and biological characteristics, covers a wide range of themes, such as a rimless wheel, a design method for a biped based on passive dynamic walking, the analysis of biped locomotion based on passive dynamic walking and dynamically inspired walking, an analysis of gait generation for a triped robot, and quadruped locomotion with a flexible trunk. Since there are interesting papers on legged robots with different numbers of legs, we basically organized the papers based on the number of legs. Studies on “Dynamically and Biologically Inspired Legged Locomotion” are expected to not only realize and improve legged locomotion as engineering, but also to reveal the locomotion mechanism of various creatures as science.

As life expectancy has become longer, the number of those who have some handicaps or diseases as well as the families, caregivers and medical staff who support them has been also increasing. While modern medical science has rapidly advanced by adopting the innovation of engineering technology especially in the fields of mechanical and electric engineering, the support for nursing, care and assistance by making use of engineering technology has only just begun. This special issue on “Nursing Engineering,” a combination of nursing and engineering, covers a wide range of themes such as the measuring equipment characterized by non-invasiveness, unconstraint and real-time for the purpose of helping patients and healthcare professionals and the development of the related technology; the development of the technology for the equipment to support recuperation, rehabilitation or convalescent life of patients; and active introduction of information technology and user interface technique into nursing study and its case studies. “Nursing Engineering” is expected to play increasingly important role to support medical treatment and everyday life of patients along with the highly professional medical staff by making practical use of the technology of robotics and mechatronics and incorporating rehabilitation science, welfare engineering and technology for assistance.

Robot audition, the ability of a robot to listen to several things at once with its own “ears,” is crucial to the improvement of interactions and symbiosis between humans and robots. Since robot audition was originally proposed and has been pioneered by Japanese research groups, this special issue on robot audition technologies of the Journal of Robotics and Mechatronics covers a wide collection of advanced topics studied mainly in Japan. Specifically, two consecutive JSPS Grants-in-Aid for Scientific Research (S) on robot audition (PI: Hiroshi G. Okuno) from 2007 to 2017, JST Japan-France Research Cooperative Program on binaural listening for humanoids (PI: Hiroshi G. Okuno and Patrick Danès) from 2009 to 2013, and the ImPACT Tough Robotics Challenge (PM: Prof. Satoshi Tadokoro) on extreme audition for search and rescue robots since 2015 have contributed to the promotion of robot audition research, and most of the papers in this issue are the outcome of these projects. Robot audition was surveyed in the special issue on robot audition in the Journal of Robotic Society of Japan, Vol.28, No.1 (2011) and in our IEEE ICASSP-2015 paper. This issue covers the most recent topics in robot audition, except for human-robot interactions, which was covered by many papers appearing in Advanced Robotics as well as other journals and international conferences, including IEEE IROS.   This issue consists of twenty-three papers accepted through peer reviews. They are classified into four categories: signal processing, music and pet robots, search and rescue robots, and monitoring animal acoustics in natural habitats.   In signal processing for robot audition, Nakadai, Okuno, et al. report on HARK open source software for robot audition, Takeda, et al. develop noise-robust MUSIC-sound source localization (SSL), and Yalta, et al. use deep learning for SSL. Odo, et al. develop active SSL by moving artificial pinnae, and Youssef, et al. propose binaural SSL for an immobile or mobile talker. Suzuki, Otsuka, et al. evaluate the influence of six impulse-response-measuring signals on MUSIC-based SSL, Sekiguchi, et al. give an optimal allocation of distributed microphone arrays for sound source separation, and Tanabe, et al. develop 3D SSL by using a microphone array and LiDAR. Nakadai and Koiwa present audio-visual automatic speech recognition, and Nakadai, Tezuka, et al. suppress ego-noise, that is, noise generated by the robot itself.   In music and pet robots, Ohkita, et al. propose audio-visual beat tracking for a robot to dance with a human dancer, and Tomo, et al. develop a robot that operates a wayang puppet, an Indonesian world cultural heritage, by recognizing emotion in Gamelan music. Suzuki, Takahashi, et al. develop a pet robot that approaches a sound source. In search and rescue robots, Hoshiba, et al. implement real-time SSL with a microphone array installed on a multicopter UAV, and Ishiki, et al. design a microphone array for multicopters. Ohata, et al. detect a sound source with a multicopter microphone array, and Sugiyama, et al. identify detected acoustic events through a combination of signal processing and deep learning. Bando, et al. enhance the human-voice online and offline for a hose-shaped rescue robot with a microphone array.   In monitoring animal acoustics in natural habitats, Suzuki, Matsubayashi, et al. design and implement HARKBird, Matsubayashi, et al. report on the experience of monitoring birds with HARKBird, and Kojima, et al. use a spatial-cue-based probabilistic model to analyze the songs of birds singing in their natural habitat. Aihara, et al. analyze a chorus of frogs with dozens of sound-to-light conversion device Firefly, the design and analysis of which is reported on by Mizumoto, et al.   The editors and authors hope that this special issue will promote the further evolution of robot audition technologies in a diversity of applications.

When first introduced half a century ago, adaptive control was half accepted as useful and half rejected as useless in industrial systems, and has greatly evolved theoretically. Learning control, a related discipline, has also been widely studied, especially in robot control. Adaptive/learning control, which incorporates the two, has become trendy in Japan and elsewhere. New design methods, e.g., data-driven controllers and the machine learning based controllers, are also attracting attention.

This special issue, which focuses on adaptive/learning control, includes 18 contributions classified as follows:

•   • Closed-loop identification and controller redesign
•   • Adaptive output feedback control
•   • Data-driven control
•   • Multirate control
•   • Computational intelligence-based approaches
•   • Applications centering on electric motors, engine systems, hydraulic excavators, rotary cranes, etc.

In addition, one review paper covers performance-driven control.

The theoretical study of adaptive/learning control has few actual applied examples in the form of real systems but is flourishing. Applied studies are expected to increasingly progress and adaptive/learning control theory holds big changes for industrial fields.

This issue is the third in a series on Real World Robot Challenge in Tsukuba. The Tsukuba Challenge has contributed much in establishing autonomous mobile robot control technology on outdoor walkways where robots must mingle with pedestrians and cyclists – not all of whom may be familiar with such robots. The rain on the day of the final run for the 2015 Tsukuba Challenge taught us valuable lessons in navigating robots in real environments. Since the 2013 Tsukuba Challenge, a new task was introduced in the second stage. This task consists of searching for human targets – a technological challenge for developing robots that are both mobile and useful. Our objective here is to share advanced control technology refined through experiments in the real-world environment of the Tsukuba Challenge. The Tsukuba Challenge is also providing a forum for technological education for university students studying robotics engineering and for technical exchange through open experiments. In this issue, we are pleased to present the control technology that this exchange has brought about. We would like to express our deep gratitude to the authors contributing to this issue and to the article reviewers who have helped make this all possible.

  Research on unmanned aerial vehicles (UAVs) has been conducted for quite some time, even though experiments were rather difficult to carry out. However, recent years have seen a proliferation of published reports in this field. This is most likely due to the spread of multicopters, which are easier and safer to operate than fixed-wing aircraft and single-rotor helicopters.   Other factors that have made it easier to conduct research on UAVs and thus contributed to the increased number of studies include the wide availability of high-performance flight controllers that are either low cost or offered on an open-source basis, such as ArduPilot and MultiWii.   Although this has minimized technological hurdles in conducting research, it has become more difficult to conduct research safely in a social and legal context. Prompted by a 2015 drone incident, Japan’s civil aeronautics law was revised to control UAV flights under stricter regulations. Even so, these regulations are still considered less restrictive than those in most other countries.   UAV research includes obvious risks and dangers of operating airborne devices, but also makes it more interesting as a scientific inquiry, generates high expectations about practical utility, and makes a highly significant area of investigation.   Placing a high priority on safety will hopefully lead to further research in this area.   This special issue covers the latest in UAV research, including

•   • UAV control system design,
•   • Studies on flight characteristics of aircraft equipped with special mechanisms,
•   • UAV applications,
•   • Studies on operational UAVs.

  Readers will find it interesting and rewarding to explore the latest UAV research trends presented in this issue.

  The construction industry is one of the largest economicalsectors in developed countries. The economical contributionof the construction industry is comparable withthe contribution of the manufacturing industry. However,the construction industry is one of the most unfamiliar areasof R&D in the robotics community. The first ideasfor construction robots appeared in the 1970s in Japan.Due to quality problems of construction works, lack ofskilled labor, low productivity, numerous accidents andfatalities and high construction demand, the first prototypesof construction robots were developed towards theend of the 1970s. Since then more than 200 constructionrobots and service robots for buildings have been developed,but only about 10% of them have been successfullyintroduced to the construction market. The developmentof on-site robots in the 1980s peaked with the developmentof integrated automated building construction sitesin the 1990s. In the beginning of the 21st century humanoidrobots were researched and tested. In the futurewe will see robots that care for the elderly and handicappedas a further development of construction robots.
  This issue gives an overview on the state of art ofrobotic technologies in construction. The introductoryarticle also relates the construction robotics developmentto the industrial robotics technology in the prefabricationsector of the 1970s, gives examples of various constructionrobotics developments of the 1980s, the integratedautomated building construction sites since the 1990s, andthe humanoid construction robotics developments and integratedindustrialization efforts of recent date. Roboticsubtechnologies such as programming, sensors, kinematics,teleoperation, navigation, human-robot interaction arepresented to the reader. During the last years much efforthas been devoted to the application of robots and roboticstechnology in construction works. Most of them are forout-door application, where the tasks are developed incomplex unstructured environments and under hazardousconditions. The construction robots introduced during thelast years have dramatically improved labor conditions,productivity and quality levels, and also have increasedthe safety conditions for operators. The nowadays constructionrobotics technology tries to take advantage ofthe last developments for control, navigation, localization,human-machine interface or sensor use. Howeverrobotics in construction is still a very challenging topic inorder to clarify many unsolved R&D issues.
  The purpose of this special issue is to provide a reviewof open issues and new developments in robotics inconstruction, ranging from major construction engineeringprojects to residential building construction:

•   • Robotics for building construction.
•   • Robotics for civil engineering: roads, bridges, earthmoving, etc.
•   • Inspection, maintenance and infrastructures robots.
•   • Navigation, mapping and localization of robots inconstruction environments.
•   • Technology components for construction robots: 3Dsensors, end-effectors, HMI, control strategies, cooperation,safety, etc.

Intelligent automobiles equipped with active safety methods whose objective is to reduce accidents caused by human problems such as careless driving and loss of consciousness, have got the social acceptance widely which are recognized by introducing collision avoidance brakes to the market. Active safety and automated driving technologies of intelligent automobiles were featured at TokyoMotor Show 2015. Their displays attracted much attention.It is necessary to propose new technologies continuously by the technical subject of active safety and automated driving, for example, relation of cooperative driving by a vehicle system and a driver, from the restrictions of originality of technical developments and the liability issues at the time of an accident.Even so, users worldwide expect much from the dynamic future of transportation for safety and active life.This special issue features seven papers carefully reviewed by field specialists.I would like to express my heartfelt appreciation to the authors who have contributed their valuable research results to this special issue and to the reviewers who provided their invaluable expertise.I would also like to thank members of the Journal of Robotics and Mechatronics board for giving me the unique opportunity to plan and coordinate this issue.

The first Tsukuba Challenge started in 2007 as a technological challenge for autonomous mobile robots moving around on city walkways. A task was then added involving the search for certain persons. In these and other ways, the challenge provides a test field for developing positive relationships between mobile robots and human beings. To make progress an autonomous robotic research, this special issue details and clarifies technological problems and solutions found by participants in the challenge. We sincerely thank the authors and reviewers for this chance to work with them in these important areas.

Robot vision is an important robotics and mechatronics technology for realizing intelligent robot systems that work in the real world. Recent improvements in computer processing are enabling environment to be recognized and robot to be controlled based on dynamic high-speed, highly accurate image information. In industrial application, target objects are detected much more robustly and reliably through high-speed processing. In intelligent systems applications, security systems that detect human beings have recently been applied positively in computer vision. Another attractive application is recognizing actions and gestures by detecting human – an application that would enable human beings and robots to interact and cooperate more smoothly when robots observe and assist human partners. This key technology could be used for aiding the elderly and handicapped in practical environments such as hospital, home, and so on. This special issue covers topics on robot vision and motion control including dynamic image processing. These articles are certain to be both informative and interesting to robotics and mechatronics researchers. We thank the authors for submitting their work and for assisting during the review process. We also thank the reviewers for their dedicated time and effort.

According to the aged society in Japan, the expectation is high for the development of the human support robot or devices in daily life and in medical treatment and welfare. The human centered design and the universal design are very important concept for creating the useful human support devices. Human centric and universal designs are the designs of products and environments to be usable by all people, to the greatest extent possible, without the need for adaptation or specialized design. This special issue provides current researches and developments of human centric, universal and interactive design for robotics and mechatronics. Also, this special issue covers a broad range of research topics, such as human centric design, universal and interactive design, human machine interaction, transport system, housing environment system, rehabilitation devices, multi modal interface, evaluation of the usability, sensor/actuator technologies for assistive system, robotics and mechatronics to support elderly persons. We thank the authors for their fine contributions and the reviewers for their generous time and effort. In closing, we thank the Editorial Board of the Journal of Robotics and Mechatronics for helping make this issue possible.