This study addresses the challenge of predicting the terrain traversability of off-road vehicles. When an off-road vehicle is operated on rough terrains or slopes of unconsolidated materials, it is crucial to accurately predict terrain traversability for efficient operations and to avoid critical mobility risks. However, the prediction of traversability is challenging, especially for the prediction of possibly risky terrains because for such terrains, the traverse data available is either limited or non-existent. To address this limitation, this study proposes an adaptive terrain traversability prediction method based on the multi-source transfer Gaussian process regression (MS-TGPR). The proposed method utilizes limited data available on low risk terrains of the target environment to enhance the prediction accuracy by leveraging past traverse experiences on multiple types of terrain surfaces. The effectiveness of the proposed method is demonstrated using a slip dataset of various terrain surfaces and geometries.

This paper proposes a new path planning algorithm to consider motion uncertainty for wheeled robots in rough environments. The proposed method uses particles to express the uncertainty propagation in complicated environments constructed with various types of terrain. Also, RRT (Rapidly-exploring Random Tree) is expanded based on the uncertainty of each node in order to prevent increasing the accumulated position uncertainty. As a result, the generated path reduces the times of path-following and re-planning based on inaccurate localization information. The effectiveness of the proposed method is evaluated in simulation using motion uncertainty models obtained by experiments. The results show that the proposed method decreases the position uncertainty while keeping the probability to avoid collisions and to reach the goal area compared with conventional approaches.

Ahstract- In this study, we propose a development and formation control of a passive mobile robot equipped only with servo brakes and no motors. The developed passive mobile robot can move forward by utilizing an external pulling force, and steers itself by controlling the servo brakes attached to each wheel. Systems composed of multiple mobile robots are very effective at exploring vast areas. However the coordination and simultaneous control of several robots utilizing simple information is a difficult task. Therefore we propose a leader follower architecture composed of multiple passive follower robots tethered to one active leader. In this paper, we first introduce the developed passive mobile robot. Then, we analyze the fundamental control method of this passive mobile robot from the perspective of the feasible braking control region, which considers the slip of the passive robot and the limitation of the external pulling force from the active leader. Lastly, a control law for the servo brakes attached to each wheel is proposed, followed by a feasibility study to determine whether the passive followers can stay in formation by controlling the servo brakes with the proposed control law.

This paper presents the characterization of the new Associative Memory chip (version 7) designed and fabricated in 28 nm CMOS. The design aims at: enhancing links from/to FPGAs; increasing bandwidth thanks to full custom LVDS transceivers; and reducing power consumption and silicon area by means of new memory cells designed with full-custom approach. The design was submitted in December 2016; the prototypes were fabricated and packaged in a 17 × 17 Ball Grid Array (BGA) standalone package. Prototype characterization confirms the chip functionality. The final chip will be assembled in a System In Package (SiP) together with a bare FPGA die.

Unmanned rescue, observation, and/or research vehicles with high terrain adaptability, high speed, and high reliability are needed in difficult-to-reach locations. However, for most vehicles, high performance over rough terrain reduces the travel speed and/or requires complex mechanisms. We have developed a blade-type crawler robot with a very simple and reliable mechanism, which traverses uneven terrain at high speed. Moreover, the gyro wheel design stabilizes the success of this approach in improving the motion, ensuring robust traversal. The improvement in traveling speed and robustness over uneven terrain by our approach was confirmed by experiment.

Sub-seafloor exploration is an important area of biological and geological research, and often requires samples of seafloor mud to be recovered. The minerals and marine sediments trapped in this mud are also potentially valuable resources. However, seabed exploration has been limited by the complexity and cost of the traditional equipment used. Wide area exploration can be made possible by deploying multiple robots to autonomously search beneath the ocean floor. In this study, we prototyped a sub-seafloor excavation robot for use in seabed exploration. The key system comprised a propulsion unit and an excavation unit that allow the robot to move freely within the seabed. We experimentally demonstrated the ability of the excavation robot to produce curved boreholes with a diameter of 160 mm, a turning radius of 1.67 m, and a depth of 613 mm. Our experimental results confirm that nonlinear excavation is possible using the excavation robot developed.

This paper proposes a novel method to estimate relative poses for a calibrated stereo camera. Three corresponding points in 3D space are theoretically required to recover unconstraint motion which has six degrees of freedom. The proposed method solves this problem with only two 3D points by exploiting a common reference direction between poses. Two points are selected in accordance with the distance to the camera: one distant point is used for deriving a reference direction, and one near point is used for estimating accurate translation. The distance is computed by triangulation in stereo vision. The uncertainty of triangulation can be mitigated by the appropriate selection strategy. The experiments using synthetic and real data demonstrate the effectiveness and higher stability of the proposed method against image pixel noise.

Difficult conditions on outdoor terrains make outdoor autonomy for rovers, a challenging task. The conventional wheel odometry method uses orientation measurements to assume a momentary plane to apply wheel encoder readings. On uneven terrains, this method often gives poor results for position tracking, and therefore rarely used. To improve the conventional odometry motion model, immediate terrain data can be used. This paper proposes a novel state variable extension (SVE) method to establish a connection between state space variables of a terrain rover by combining terrain point clouds with rover kinematics. The simulation results show that when the 2D state variables (x, y, yaw) are known, the 2D state can be extended to its 3D state (x, y, z, roll, pitch, yaw) with minimal error. The proposed SVE method is employed in a particle filter to determine the 2D state variables, which in turn results in achieving the full 3D position tracking of the rover.

We have developed an exclusive planetary sub surface explorer robot with propulsion and excavation units. In this paper, we first explain the concept of our underground explorer robot. Next we develop an excavation unit with a tapered earth auger and a propulsion unit with dual pantograph. Several experiments are performed to demonstrate these features. Finally, we develop a subsurface explorer robot with propulsion and excavation units. Excavation experiments are successfully conducted using the excavator alone and at lighter weights. We show that the excavator can begin boring from a launcher, and in case of excavator of 1/6 of its own weight, it successfully excavates at the same depth as in its own weight. This demonstrates that this novel excavator is expected to accomplish future missions on other planets and the moon.

This paper describes the mathematical modeling and the propulsive characteristics of a novel robot driven by Archimedean screw mechanisms, named Screw Drive Rover. For secure locomotion on soft soil, the proposed rover would become one of the good solutions because of its robustness to slipping and getting stuck in the soil. Furthermore, the rover is expected to move in various directions by using the dual screw units. However, the interaction between such screw unit and the surrounding soil is quite complicated and remains undefined. So, this paper attempts to model the tractive effort of the rover on the soil. The mathematical modeling is newly developed based upon terramechanics, addressing soil-vehicle interactive mechanics. Finally, the validity of the proposed model is demonstrated by simulation analyses.

We present a two-step iterative algorithm to estimate the trajectory of a hopping rover. In the first step, a monocular scheme of visual odometry is adapted to estimate an initial portion the hopping trajectory. From this, the parameters for the ballistic motion are recovered, and the trajectory is extrapolated to predict the positions of the rover for the remainder of the hop. In the second step, we devise a scheme called ¿selective vision¿, combining the ideas of active vision and guided search. An envelope lying between the start and end of a hop is defined, within which features most likely to be re-observed across a hop are detected and matched. Performing pose estimation on the these matched features allow the relative motion between a camera frame within the visual odometry step and a camera frame within the extrapolated trajectory to be estimated. The newly determined camera frame in the extrapolated trajectory can then be used to refine the parameters of the ballistic motion, and the trajectory can be re-extrapolated to predict future positions of the hopping rover. Following this scheme, it is possible to estimate the trajectory of a hopping rover undergoing continuous rotational motion with only one set of cameras without continuous tracking of terrain features.

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on descent and touchdown dynamics are shown and discussed.

A new lunar exploration mission including a lander and rovers is under studying in Japan. The main mission for lunar robotics exploration is to demonstrate the technologies for lunar or planetary surface exploration. They will cover pin-point landing technology, reliable landing scheme with obstacle avoidance, landing mechanism on rough terrain, exploration rover and tele-science technology. Lunar geologic survey will be also performed to investigate the underground materials. The working group has been conducting the feasibility study of advanced technologies for lunar robotics exploration. In the rover mission, a robotic manipulator plays an important role as scientific observation tools for geological exploration. This paper proposes a light-weight manipulator with low-power consumption function. To investigate the effectiveness of the proposed design, a manipulator was developed. This paper describes a proposed smart manipulator system. This paper also presents the environment test results on Ultra-Sonic Motor. The performance of the developed smart manipulator is discussed.

Lunar rovers are required to move on rough terrains such as in craters and rear cliffs where it is scientifically very important to explore. Recently, wheel typed rovers are popular for planetary exploration missions. However, there is a problem that the wheel typed rovers have possibility of stack. Therefore, this paper investigates a mechanism of kinetic behavior between the wheels of the exploration rovers and soil. The important parameters are extracted by considering the mechanism. This paper proposes an elastic wheel by considering the important parameters. The elastic wheel has the surface which can be changed flexibly toward rough terrain. Running experiments on soil which imitated regolith are carried out to observe the traversability of the elastic wheel using slip ratio and sinkage.

Subsurface exploration on the Moon is a significant mission for future space developments. The authors have studied an autonomous robotic explorer which can burrow into the soils. This paper focuses especially on the excavation mechanism of a burrowing robot for near-future lunar subsurface exploration. The main objective of the proposed robot is to bury a scientific observation instrument, such as a long-term seismometer under the lunar surface, which is covered with very compacted lunar regolith. Therefore, an efficient drilling mechanism is required. In this paper, the authors propose a non-reaction screw drilling mechanism with double rotation, which is called the contra-rotor screw. This paper also evaluates the feasibility and effectiveness of the proposal of a burrowing robotic system through some experimental analyses.

This paper describes a position identification method to precisely estimate the relative movement onboard of an autonomous explorer in such natural terrain as Moon or Mars. This paper proposes a new map matching scheme that registers the visual information of consecutive robot positions and expresses the robot displacement in a common coordinate system. Local elevation maps of the environment are therefore retrieved from the 3D perception of a stereo camera. The proposed scheme consists of three main steps: feature point extraction from map data, matching of features points using triangle configurations and a voting procedure, and direct calculation of the robot displacement in six degrees of freedom using quaternions. The effectiveness of the proposed method is confirmed by computer simulations with synthetic terrain and experiments with stereo perception.

Planetary exploration requires rovers to perform a variety of challenging tasks autonomously. In order to complete relevant scientific mission, these rovers need to overcome difficulty for rough terrain traversing by "online methods". This paper discusses an idea that utilizes a rover mobile center of mass in order to aid in traversing rough terrain. According to vehicle pitch angle and contact angles, the rover recalculates the optimal position for the center of mass to minimize the indicator defined by two factors : the wheel driving force over the wheel normal force (adhesion coefficient) and tip-over stability angle (stability coefficient). Two innovative approaches are developed in this paper. The first one is that the authors defines easily comprehensible two factors, adhesion and stability coefficients for traversability indicator and proposes a method to calculate optimal center of mass position. The second one is that in the case of four-wheels drive, the relation between the front wheel and the rear wheel adhesion coefficient is easily solved and the best case for giving the driving forces can be solved as force making the front and the rear wheel adhesion coefficient equal. The authors call this "optimal force distribution method". Finally, this paper shows some simulation results for traversing rough terrain that compute the optimal center of mass while traversing the terrain.

In future planetary exploration missions, robots are required to traverse over very rough terrain. On the surface of the moon there are covered with soils, which is named regolith. Regolith is easy to slide. Any stack may occur to the robots that are running on the regolith. Some researchers have studied the mobility system for robots. However the optimal and robust mobility systems have not been developed yet. For producing high traversability, this paper proposes a new wheel system, considering the characteristic of soil made a new wheel

The MUSES-C mission is the world first sample and return attempt to or from the near Earth asteroid. In deep space, it is hard to navigate, guide, and control a spacecraft on a real-time basis remotely from the earth mainly due to the communication delay. So autonomy is required for final approach and landing to an unknown body. It is important to navigate and guide a spacecraft to the landing point without hitting rocks or big stones. In the final descent phase, cancellation of the horizontal speed relative to the surface of the landing site is essential. This paper describes various kinds of robotics technologies applied for MUSES-C mission. An autonomous descent scheme and a novel visual navigation system are proposed and presented in detail. The validity and the effectiveness of the proposed methods are confirmed and evaluated by numerical simulations and flight results

In operation environment with communication time delay, it's difficult to compose a closed loop control structure between a master and a slave system, and some scheme to achieve the stability is thus necessary. In this paper, we discuss and evaluate our proposed human machine cooperative tele-drive system that consists of global and local path-planning, for long range traversability. The operator can command any desired path as a sequence of waypoints by using a 3D terrain model measured as DEM by the on-board sensor of a rover. The data is transmitted to the ground and evaluated to obtain a dangerousness map. To cope with an unknown obstacle, a conventional autonomous path-planning algorithm is applied between each waypoint. In addition, a rover is continuously updating its knowledge about the environment. By continuously recalculating the difference between the original terrain data used for initial path generation on the ground and the most recent data acquired by the rover, a waypoint compensation can be achieved. Therefore, we have to compensate waypoints by using the latest measurement data which can be assumed more reliable than previous data, for corresponding to the difference automatically. Here, the difference is assumed as the distortion between each data set, and compensated by using a distortion compensation matrix which is the mapping between the old and new terrain data sets. Simulation and experimental results and its evaluations by using the rover test-bed are mentioned in the paper

This paper presents a mobile robotic system designed to perform deep soil sampling for lunar subsurface exploration in the near future. Drilling robots have to carry the excavated regolith backward because of its high density. Therefore a new scheme is proposed, to move forward under the soil by making use of reactive force caused by pushing the discharged regolith. Simple experiments demonstrate the effectiveness of the proposed method.

Planetary exploration robots are required to explore rough and steep areas such as craters and cliffs to achieve scientific goals. Most of the proposed rovers have some wheels to move on a planetary surface. However, it is difficult to traverse on a rough terrain flexibly. A legged rover can provide higher capability of moving in such a rough terrain than wheeled robots. Therefore the authors have studied a small and lightweight rover which can move across a rough terrain such as a steep slope inside craters. This paper deals with design scheme for a light walking rover for planetary exploration. This paper presents analysis on the proposed weight arrangement scheme to reduce the weight of the walking robots. The effectiveness of the proposed scheme is shown by computer simulation and hardware study.

In order to evaluate mobility performance of roving vehicles on natural terrain of the other planets, a number of running tests on the Earth have to be carried out in consideration of the difference of gravitational acceleration. In this paper, the authors focus on the analysis with similarity models and experimental study to take the difference of gravity into account. The authors introduce two similarity models of the planetary rovers for 1G or 1/2G gravity experiments, respectively to examine the similarity law itself and the performance of the mobility systems. This paper presents the experimental results for both low-gravity flight tests by the airplane and the tests on the ground.

This paper proposes a localization method to estimate position and azimuth of a lunar rover. In the proposed method, the position is precisely estimated by integration of an absolute and a relative position. The absolute position is measured by observing the sun and the earth, and the relative position is determined by dead reckoning. Effectiveness is confirmed by the results of simulations. Moreover, differences between proposed method and Extended Kalman Filter are shown by results of long-distance simulation.

In order to carry out experiments many times on the Earth in consideration of the difference of gravitational acceleration to design the rover properly, we introduce similarity law to design and construct the experimental models. We have produced two experimental models of the planetary rover with 5-wheel suspension system (called "PEGASUS") and 4WD system under for 1G and 1/2G gravity. We have carried out a low-gravity flight experiment in various parameters using the model on the airplane. Assuming that similarity law is true under every gravity environment, we have made relative evaluation on a degree of mobility by the difference of mobility systems. In the result of the flight experiment, it is show that PEGASUS is able to successfully move better than 4WD.

Hopping is effective mobility for exploration robot on small body. To explore small bodies, a mobile robot is required to move to target points. In case of exploration of microgravity environment by a hopping locomotion, hopping trajectories cannot be controlled after a robot hops. To move to target points, hopping direction and velocity should be controlled at takeoff. The authors proposed a, hopping robot, which consists of three masses, two linear actuators and a spring. This paper discusses how to control a hopping direction of the proposed robot in microgravity environment. When the robot hops, the friction force between the robot and the ground becomes larger. The simulation results show the controllability of a hopping direction even if there is a slip on a ground. The controllability is also confirmed by the free fall experiments.

Performance of mobility is highly dependent on the gravitational environment. Some researchers have proposed novel locomotion methods for extremely small terrestrial bodies like asteroids. Hopping is a possible method under micro-gravity. It is not proved, however, that the proposed method of locomotion is optimum for a given level of gravity. The purpose of this paper is to analyze which level of gravity is optimum for each mechanism, and which mechanism or parameter is optimum for each level of gravity. First, a classification of locomotion mechanism is described. Next, the speed of hopping and wheeled robots is compared. Finally, some simulation studies are performed to analyze the detailed mobility of wheeled robots.

This paper proposes a hopping robot that can move in a microgravity environment. The robot consists of three masses, which are connected by a spring and linear actuators. Using the spring and the linear actuators, the robot can obtain the vertical velocity and the horizontal velocity. Therefore, the robot can hop with the horizontal velocity from the stationary state. Furthermore, the robot can land without bounding and the slipping by transforming the kinetic energy to the elastic energy. Using this approach for controlling hopping and landing, the robot can move to a target in a microgravity environment. The simulation studies and the microgravity experiments shows the effectiveness of the proposed mobility.

This paper proposes a new mobility system for planetary rover using springs and linear actuators. In the microgravity environment, hopping mobility is a possible choice for enhancing a new mobility of the robot. One method to hop is to press one's own to the ground. The proposed robot consists of two masses, and can press one's own to the ground using springs. So the rover can hop from the stationary state by transforming the elastic energy to the kinetic energy using the springs and linear actuators. Furthermore the robot can land without bounding by transforming the kinetic energy to the elastic energy. The simulation studies and the ground experiments shows that the proposed rover could hop and land.

This paper proposes a four-wheel-type robot with the springs and linear actuators mechanism. In the microgravity environment, hopping mobility is a possible choice for enhancing a new mobility of the robot. The proposed robot can hop and land without bounding in the microgravity environment using the spring mechanism. Furthermore, at the moment of hopping, the wheels are pressed to the ground, so the rover can obtain the horizontal velocity by rotating the wheels. The wheels are also used for the attitude control in the air. The simulation of hopping with horizontal velocity is performed and the equation of kinematics of the rover is developed.

This paper describes the path planning method for a planetary microrover. A planetary rover is required to travel safely over a long distance for many days in unfamiliar terrains. Hence it is very important how a planetary rover processes sensory information in order to understand the environment and to make decisions. The authors have newly developed a small rover for future lunar or planetary exploration. As a new data structure for map information, an extended elevation map is introduced, which includes the effect of the size of the rover. The proposed path planning can be conducted in such a way as if the rover were a point while the size of the rover is automatically taken into account. The map obtained by sensors includes uncertainties. Thus a path planning scheme based on traversability and probability is also proposed. The validity of the proposed method is verified by computer simulations.

We discuss a tele-driving system for distant driving of a lunar rover, and describe our newly developed small, lightweight lunar rover called Micro-5 and its visual sensor system. The operator uses a virtual world simulator to make command path. The virtual environment of this simulator is constructed with measurement data from the rover on the moon. However, there is a communication delay between the earth and the moon. So, there is a difference between the old map data which the operator used for path planning and the new data which the rover is tracking. The operator's path command is thus less reliable to avoid obstacles and to reach the goal. Therefore, to achieve a highly reliable operator's command, we propose a command-data compensation approach which compensates this difference as the distortion of the environmental map.

In a new stage of space development, collision and contact tasks under micro-gravity, such as docking, orbital servicing, and touchdown to a minor body, are now increasingly being considered. A hybrid motion simulation consisting of both physical and numerical models is an effective method to test the motions of a spacecraft under zero G on the ground. The authors have developed a hybrid zero G motion simulator based on a highspeed parallel link mechanism. A wide response bandwidth and high stiffness of the simulator have made it possible to simulate the contact motions with high precision. In this paper, they evaluate analytically the simulator characteristics and verify experimentally the impact of dynamics on the hybrid motion simulation by comparing it with a collision experiment under zero G in a drop-shaft facility. The results imply that the simulator is highly reliable for the impact dynamics simulation under zero G.

This paper proposes a direct geographic recognition scheme from a gray-scale image without shape reconstruction. Several geographic categories are expressed in 3 /spl times/ 3-arrays of normal-vector directions. Only by looking up a table, the observed pixel-values (intensities) in a window are transformed into indices of conformity whether the scene in the window is due to each geographic category or not. Geographical features are extracted by multi-resolution interpretation and fuzzy-logical operations. The feasibility and robustness of the proposed method is shown by some computer simulations.

We discuss a tele-driving method for long-range driving of a lunar rover. An operator uses a virtual world simulator to make a command path. The virtual environment of this simulator is constructed with measurement data from a rover on the moon. We have, however, a communication delay between the earth and the moon. So, there is a difference between old map data which the operator used for path planning and new data, which a rover is tracking on. The operator's path command has less reliability for avoiding obstacles and to reach the goal. Therefore, to make the operator's command highly reliable, we propose Command-Data Compensation, which compensates this difference as the distortion of the environmental map.

Under the micro-gravity environment such as on the surface of small planetary bodies (asteroids or comets), traditional wheeled rovers are not expected to move effectively due to the low friction and inevitable detachment from the surface. Therefore, the authors propose a hopping rover suitable for exploration on the surface of small bodies. This paper describes the micro-gravity experiments of a proposed hopping rover which is driven by an internal DC motor torque. The proposed rover could hop under a micro-gravity environment. Experimental results are compared with the computational simulations.

Under the micro gravity environment, such as on the surface of small planetary bodies (asteroids or comets), traditional wheeled rovers are not expected to move effectively due to the low friction and the inevitable detachment from the surface. This paper discusses the friction-based mobility around the surface of small bodies and proposes a new mobility mechanism that drives the rover by hopping. The hop angle and the velocity are analyzed by numerical simulations, which show the effectiveness of the new mobility system.

For evaluating the basic navigation techniques for a planetary rover on a natural terrain, long range navigation experiments had been performed at Mt. Mihara volcano of Izu-Ohshima Island in September of 1996. The experimental rover succeeded in traveling over 800 m autonomously without hitting any obstacle. This paper describes navigation functions installed in the test-bed rover. This paper also presents the results obtained during the first long range navigation test.

This paper describes a practical method for autonomous capture of a target satellite in space using an on-board manipulator. In retrieving a satellite, a reference trajectory for control of the manipulator is generated with time delay due to the processing time of the target motion estimator and the manipulator controller. Consequently, the control system shows a poor performance and the end-effector sometimes fails to capture the target satellite. To solve this problem, a control system is proposed, which utilizes predictive trajectory based on the target satellite dynamics. The validity and the usefulness of the proposed control method are shown by computer simulations and experiments using a 3D hardware simulator with 9 degrees of freedom.

In autonomous retrieval of a free-flying object, tumbling motion makes it difficult to grapple the objects with an on-board manipulator. This paper presents a new control scheme to capture a tumbling satellite based on a simple dynamical model. The target motion is estimated based on visual information using Kalman filtering technique. The capture planning based on the proposed model becomes simple because the motion of a grapple fixture on a target satellite nearly stops relative to the end-effector of a manipulator. The validity and the usefulness of the proposed method are shown by computer simulations and experiments using a 3-D hardware simulator with 9 degrees of freedom.