Kazuo Ishii

Long-term and repeated observation of shallow seafloor environments is required to evaluate temporal changes in seagrass meadows and other coastal ecosystems. In this study, we propose a cable-restricted observation system consisting of an underwater vehicle, a tether cable, and a seafloor station equipped with a reel. The vehicle can repeatedly cruise over a designated area along nearly the same trajectory using the cable constraint. A design flow was developed to determine system parameters, including the reel radius, the number of cable turns, and the thrust required for the vehicle. In addition, a vehicle position model based on an involute curve and a motion model considering cable deflection were introduced. To evaluate the proposed system and trajectory model, water tank test and a sea trial were conducted using a 2.5 m tether cable. The radii of reels were 0.084 m and 0.775 m in the water tank test and sea trial, respectively. The experimental results confirmed that the vehicle could repeatedly cruise along approximately the same trajectory by winding and unwinding the cable. In the sea trial, the maximum differences between the measured and estimated positions were 0.541 m in the x-direction and 0.643 m in the y-direction. These results demonstrate the feasibility of the proposed system for repeated observation of a specified seafloor.

As robots become increasingly integrated into society, a future in which humans and robots collaborate is expected. In such a cooperative society, robots must possess the ability to predict human behavior. This study investigates a human–robot cooperation system using RoboCup soccer as a testbed, where a robot observes human actions, infers their intentions, and determines its own actions accordingly. Such problems have typically been addressed within the framework of multi-agent systems, where the entity performing an action is referred to as an ‘agent’, and multiple agents cooperate to complete a task. However, a system capable of performing cooperative actions in an environment where both humans and robots coexist has yet to be fully developed. This study proposes an action decision system based on self-organizing maps (SOM), a widely used unsupervised learning model, and evaluates its effectiveness in promoting cooperative play within human teams. Specifically, we analyze futsal game data, where the agents are professional futsal players, as a test case for the multi-agent system. To this end, we employ Tensor-SOM, an extension of SOM that can handle multi-relational datasets. The system learns from this data to determine the optimal movement speeds in x and y directions for each agent’s position. The results demonstrate that the proposed system successfully determines optimal movement speeds, suggesting its potential for integrating robots into human team coordination.

The vast ocean, which accounts for 70% of the Earth’s surface area, contains abundant minerals, energy, and biological resources, and surveys have been conducted in various ocean areas in recent years. It is extremely difficult for humans to conduct direct underwater surveys. Autonomous underwater vehicles (AUV) are expected to serve as platforms for surveying marine resources widely distributed throughout the vast ocean. However, owing to disturbances such as tidal currents, AUVs are unable to control there position well, making waypoint tracking difficult and preventing the observation of targeted observation points. In this research, to improve the robustness of AUVs in a tidal environment, we design a disturbance observer that estimates tidal currents as disturbances, and estimate tidal currents based on the results of actual diving surveys in actual sea areas using AUVs.

Communication with the underwater vehicles during their tasks is one of the most important issues. The need for real-time data transfer raises the necessity of developing communication systems. Conventional underwater communication systems, such as acoustic systems, cannot satisfy applications that need a high transmission data rate. In this study, we investigate the radio frequency communication system in seawater, which is crucial for real-time data transfer with underwater vehicles. The experiments were in a water tank full of seawater and a real environment in the ocean. Three types of antennae were used: loop antenna, wire antenna, and helical antenna. An Autonomous Underwater Vehicle (AUV) is used as a transmitter to measure the transmission rate as a function of distance. The helical antenna showed better performance regarding the coverage area. Furthermore, the AUV could move freely within the helical and capture live video streaming successfully. This investigation underscores the potential of radio frequency communication systems for enhancing underwater vehicle operations, offering promising avenues for future research and practical implementation.

Underwater communication is one of the most important and difficult challenges facing researchers due to the high attenuation of the signal, communication with the surface because of the harsh medium of water, and data transmission performance degradation as a result of various effects. Underwater acoustic communication (UWA) has a low data rate, which describes the disadvantage of this type of communication. In addition, it has a low bandwidth range and high latency but has a long transmission range as an advantage. Multicarrier wireless transmission systems increase the data rate by sending the data using more than one carrier. We proposed a noncoherent orthogonal frequency division multiplexing (OFDM) method to increase the data rate in UWA communication systems. In addition, doubling the data rate in the OFDM using Subcarrier Power Modulation (OFDM-SPM) system can save half of the bandwidth. The MATLAB simulation program was used to implement the system in the underwater acoustic environment to increase its throughput. The proposed design uses Differential Phase Shift Keying (DPSK) with power control, and the data stream is transmitted through two-dimensional modulation schemes, the DPSK, and the power level of each subcarrier in the OFDM system with cyclic prefix (CP). The underwater channel was designed using a Rician fading multipath with a spreading loss formula as a function of distance and frequency. We designed an equalizer at the receiver side to recover the original signal as a function of three parameters which are: the channel effect as a rate between transmitting and receiving symbols, the Rician channel response, and the UWA spreading loss. OFDM-Subcarrier Power Modulation (OFDM-SPM) using the proposed equalizer performed better than the theoretical OFDM-SPM in the Rayleigh channel. The designed equalizer increased the performance of the OFDM-SPM system by 25% which helped to enhance the system’s throughput and doubled the data rate compared with the OFDM system, doubling the data rate using OFDM-SPM had been validated in laboratory experiments in the Time domain.

The use of innovative mobile vehicles with increasingly advanced mechatronic aspects in the agricultural sector is becoming, in recent years, a stimulating field of research and comparison. In particular, the problem addressed in the present work refers to improving the locomotion of mobile vehicles on agricultural terrain by reducing the soil damage and improve the overall performance. Agricultural vehicles generally use tracks and wheels for locomotion; the main difference between the two systems is the contact area with the ground and, consequently, the pressure distribution. The present work presents a new reconfigurable agricultural vehicle that can switch from one locomotion system to another, choosing the suitable configuration according to the terrain conditions. All the mechanical and electronic aspects of the prototype developed are analyzed together with an in-depth analysis of the management of the innovative functions through a user-friendly graphical interface able to control the vehicle.

Title: Grid Map Correction for Fall Risk Alert System Using Smartphone | Keywords: electronic travel aids, smartphone application, negative obstacle detection | Author: Daigo Katayama, Kazuo Ishii, Shinsuke Yasukawa, Yuya Nishida, Satoshi Nakadomari, Koichi Wada, Akane Befu, and Chikako Yamada

Tracks and wheels are the most widely used running gear for the locomotion of agricultural vehicles. The main difference between the two systems is the contact area with the ground and, consequently, the pressure distribution. Evaluating the pressure distribution on the ground is important because soil damage and vehicle performance depend on it. This analysis is especially difficult for tracked vehicles, owing to their complexity compared with wheeled systems. In this paper, we describe a multibody model of a flexible track to evaluate the pressure distribution upon contact with soft terrain. The track considered in this study is part of a reconfigurable locomotion system of a small farming vehicle, which can vary the pressure distribution by switching from a wheeled vehicle to a half-tracked vehicle. The aim of such a vehicle is to minimize soil damage in addition to optimizing its performance. The model is used to characterize this vehicle and evaluate the pressure distribution with varying characteristic parameters, such as track tension, the position of the vehicle’s center of gravity, the weight distribution on the track itself, and the stiffness of the suspension system.