久保田 孝

<title>Abstract</title>In this paper, a novel terrain traversability prediction method is proposed for new operation environments. When an off-road vehicle is operated on rough terrains or slopes made up of unconsolidated materials, it is crucial to accurately predict terrain traversability to ensure efficient operations and avoid critical mobility risks. However, the prediction of traversability in new environments is challenging, especially for possibly risky terrains, because the traverse data available for such terrains is either limited or non-existent. To address this limitation, this study proposes an adaptive terrain traversability prediction method based on multi-source transfer Gaussian process regression. The proposed method utilizes the limited data available on low-risk terrains of the target environment to enhance the prediction accuracy on untraversed, possibly higher-risk terrains by leveraging past traverse experiences on multiple types of terrain surface. The effectiveness of the proposed method is demonstrated in scenarios where vehicle slippage and power consumption are predicted using a dataset of various terrain surfaces and geometries. In addition to predicting terrain traversability as continuous values, the utility of the proposed method is demonstrated in binary risk level classification of yet to be traversed steep terrains from limited data on safer terrains.

<title>Abstract</title>Hopping robots, called hoppers, are expected to move on rough terrains, such as disaster areas or planetary environments. The uncertainties of the hopping locomotion in such environments are high, making path planning algorithms essential to traverse these uncertain environments. Planetary surface exploration requires to generate a path which minimises the risk of failure and maximises the information around the hopper. This paper newly proposes a hopping path planning algorithm for rough terrains locomotion. The proposed algorithm takes into account the motion uncertainties using Markov decision processes (MDPs), and generates paths corresponding to the terrain conditions, or the mission requirements, or both. The simulation results show the effectiveness of the proposed route planning scheme in three cases as the rough terrain, sandy and hard ground environment, and non-smooth borders.

This paper presents a novel algorithm that estimates energy consumption of exploration robots for the efficient mobility in natural terrain. The energy estimation method is beneficial to the energy management problem to establish the robot autonomy, especially in energy-limited environments such as planetary surfaces and isolated volcanoes. The key idea of the proposed approach is to employ the terrain classification into the dynamics-based energy estimation model, so that it can adapt to the variability of terrain properties. A vibration-based terrain classifier is proposed in this paper, which analyzes vibration signals in the time-frequency domain and learns terrain patterns by a supervised learning technique. The terrain classification results are used to determine terrain-dependent parameters in the energy estimation model. A field test has been conducted in a volcanic field to show the validity of the proposed algorithm. The proposed method successfully demonstrates the capability to estimate energy consumption, while it raises discussions about determining terrain types in real natural terrain.

&lt;p&gt;We are planning to explore the caverns through the skylight holes on the Moon and Mars. The holes and their associated subsurface caverns are among the most important future exploration targets. The importance of the lunar and Martian holes and their associated caverns is categorized from two aspects: (1) fresh materials are easily observed and sampled there, and (2) the subsurface caverns provide a safe, quiet environment. The expectation of lunar and Martian hole and cavern exploration is increasing in Japan. We name the project as UZUME (Unprecedented Zipangu (Japan) Underworld of the Moon Exploration) whose name is after a Japanese mythology. The ultimate purpose of the UZUME project is to investigate how to expand human activity and survival in space and on extraterrestrial bodies.&lt;i&gt;&lt;b&gt; &lt;/b&gt;&lt;/i&gt;&lt;/p&gt;

Recently, planetary investigations have accumulated basic data through various aerospace explorations. However, the investigations of underground such as moonquakes, heat, and conditions of the soil have not revealed much. Therefore, the authors have developed a novel, small planetary subsurface excavation robot that uses the peristaltic crawling of an earthworm as its underground propulsion method. In this study, the authors focused on two types of geotechnical tests: pressure meter and shearing tests using the excavation robot. These tests were conducted by measuring displacement and force in the radial and vertical directions inside the soil, using the excavation robot&#039;s own hardware system. This paper describes these geotechnical tests, which used the propulsion unit of the robot and measured the soil parameters, e.g., internal friction angle, adhesibility, and elastic constant. From the experiments, the authors evaluated and discussed results by comparing with reference data. The authors confirmed that the propulsion unit could measure the soil parameters and propel itself underground at the same time.

Soft soils cover on planetary surfaces, so the wheels for exploration rovers easily slip. Understanding an interaction between a wheel and soft soils is important for a traction control to improve rover traversability. The interaction between the wheel and soft soils has been studied in a field of terramechanics. Since the classical terramechanics-based wheel model considers only a static state of a wheel sinkage, the wheel model is not applicable to the wheel sinkage and slip. Thus the dynamic normal stress model and shear deformation model were proposed to deal with the problems of the wheel sinkage and the slip. The dynamic normal stress model was proposed by considering the wheel sinking velocity and a variation of soil state for solving the problem of wheel sinkage. And the shear deformation model was proposed by considering the shear characteristics for solving the problem of wheel slip. The shear deformation model was formulated by the shear test. The simulation verified the validity of the dynamic normal stress model and the shear deformation model in the transient state. In this paper, a single wheel experiments was performed to evaluate the shear deformation model by comparing the simulation results and the experimental results. Then the characteristics of the wheel sinkage and slip and the effectiveness of the model were confirmed.

In recent years, to cope with low carbon society and diversification of individual mobility, new kinds of vehicles have received a lot of attention to expand our mobility. This paper proposes a new concept of vehicle named portable personal vehicle. The proposed portable personal vehicle is small and light enough, which enables not only to carry the driver but also to be carried by the driver. The proposed portable personal vehicle can easily overcome barriers in mixed traffic such as university campus, airports, shopping malls etc. It is harmless to surrounding pedestrians. This paper describes a developed inverted pendulum vehicle based on the concept of portable personal vehicle.

As of today, several rovers have been deployed on planetary surfaces and provided astonishing scientific achievements. A significant challenge in future missions is accurate localization for long distances to expand the activity range. After the successful Mars Exploration Rovers mission, visual odometry is regarded as a promising technique to provide accurate pose estimates on planetary surfaces. However, it should address the problem of terrain dependency since it cannot estimate motion in the terrain where visual features are lacked. This paper proposes a visual odometry system for untextured natural terrain which is devoid of features. Several key techniques are presented including a scheme for terrain-adaptive feature detection, and a motion estimation method using fewer feature points. The feasibility of the proposed techniques is supported by the field tests in a volcanic field using a test-bed rover.

Power source and sensing of self position are commonly required for mobile robots. Recently, wireless power transmission and position sensing from the systems embedded in the surrounding space are proposed as effective measures. Since wireless power transmission and position sensing are regarded as totally different functions, they have been realized by independent systems. However, combining multi-function into a single system has various advantages such as cost down and space-saving. Therefore, in order to realize both functions in single system, the authors have researched on position sensor via magnetic resonance coupling which have been used in the wireless power transmission field. However, there were several problems in the prototype system using arrayed transmitter antenna such as, reduction of Q factor due to the increase of wire length, the compensation capacitance values have to be set individually and antenna alignment are fixed. Therefore, as a solution, position sensor using relay antennas via magnetic resonance coupling is proposed in this paper. The novel position sensing method is proposed and evaluated through the position sensing experiment assuming mobile robot as the target.

Developing autonomous mobile robots that can coexist with human in populated environments is still considered a big challenge. To address this problem the authors propose a novel scheme to assist mobile robots by providing localization information externally. This scheme combines the autonomous navigation and target tracking research fields to arrive at a structured assistance system for autonomous mobile robots. In the proposed scheme, the environment is sensed using a laser range finder and a camera based sensor unit. Using the Rao-Blackwellized particle filter technique, the robots that need assistance are continuously tracked. In contrast with conventional laser range finder based tracking systems, the placement of the sensor is changed to a level above average human height and the mobile robots are modified by attaching a cylindrical pole. The experiments showed the validity of the proposed scheme for simultaneous localization assistance for multiple mobile robots. Two mobile robots were simultaneously navigated in given trajectories using assistance data, successfully.