A system is expected to facilitate coordination among multiple construction machines or robots, enabling them to adaptively perform various tasks in disaster sites and unknown environments. Prior research has generally adopted a model-based approach to designing cooperative behavior. However, it is difficult to adapt to environments and scenarios that cannot be predicted by the model. In recent years, it has been reported that a robot equipped with foundation models can adapt to unknown (open) environments and unpredictable situations. However, there has been little discussion on foundation models for multiple robot systems; a flow that cooperatively handles unexpected events does not exist. In this paper, we propose the system flow that enables multiple robots to adaptively coordinate to unforeseen scenarios based on the functional expressions of each other and environment understanding utilizing GPT-4 and GPT-4V. Through experimentation, we verify that the proposed flow is able to adapt to an unforeseen environment, particularly path obstruction via robot experiments. Furthermore, we examine the validity of the proposed flow by varying the robots’ functional expressions and sensor information for the environment.

Backhoe loads sediment onto the bed of dump trucks during earthmoving work. The prediction of backhoe loading time is essential for ensuring safe cooperation between the backhoe and dump trucks. However, it is difficult to predict the instant at which the backhoe is ready to load sediment, because of the similarity in motions observed during gathering sediment. Moreover, since operators have different skill levels, the prediction requires a unique model for each operator. In this study, we attempt to predict the instant at which the backhoe is ready to load sediment into the dump truck. For this purpose, the beta-process hidden Markov model (BP-HMM) is employed to build a backhoe motion model for a specific operator. Time series data of backhoe loading motions for crushed rocks and wood chips, which were measured using 6-axis inertial measurement unit (IMU) sensors equipped at the cab, boom, and arm of the backhoe, were used for modeling with the BP-HMM. Several primitive motions of the backhoe, which occur at the completion of preparation before the loading process begins, were discovered as a result of the motion modeling based on the BP-HMM. We developed the prediction of the instant using three primitive motions. At best, the proposed method could predict the instant with a probability of 67% and 100%, at 6.0 s and 0.7 s before the loading motions began, respectively. This phased prediction can be used to reduce the idle time and risk for dump trucks during earthmoving work with the backhoe.

We introduced the disturbance degree of ground and proposed an evaluation method to measure the mobile performance of a crawler on soft ground during direction switching. First, we developed a planar omnidirectional crawler, which had a configuration with two left and right unit crawlers for performing turning motion, as the target for evaluation. Second, by utilizing the proposed disturbance degree of ground evaluation method, we investigated how the turning and translational motions of the crawler mechanism affected soft ground by measuring the flow of sand on a horizontal surface. It was quantitatively shown that translational motion switched the travel direction with lesser disturbance to the road surface compared to turning motion. We confirmed that ground disturbance could be evaluated during direction switching using the proposed method.

Observations of fumaroles are important in forecasting volcanic eruptions. However, such observations are dangerous for humans because of volcanic gases and high-temperature steam that surround fumaroles. In previous study, a teleoperated mobile robot was developed to realize remote observations. However, it was observed that typical mobile robots were unable to reach fumaroles on a steep cliff. Therefore, extant research focused on the development of tethered small mobile robots to tackle thsese types of challenging cliffs to observe fumaroles. This study proposes a design of a tethered mobile robot to traverse a steep slope based on the analysis of slip and turnover. A few indoor experimental studies and field experiment were performed to verify the proposed design.

A wheeled mobile robot traveling on loose soil has wheels with grousers (i.e., lugs) on their surface to improve its mobility performance. Although previous studies have analysis and modeling of the mobility performance of a wheel with grousers, most of them did not cover the stress distribution of the wheels. In this study, we measured the three-dimensional forces acting on the grouser and three locations of the wheel surface, respectively. The stress distributions generated beneath the wheel with grousers at every angle of the wheel rotation were represented based on the three-dimensional force data. The stress distributions showed that the shear stress hardly affects the wheel surface between each grouser.

Small multirotor unmanned aerial vehicles (UAVs) are suitable for surveillance or inspection operations, such as disaster site observations or building inspections, as they can hover. Therefore, engineers and associations plan to use them for civilian applications. However, the payload capacity of current UAVs is too small to carry heavy sensors or batteries. Thus, improving payload capacity by increasing the number of rotors has been considered to achieve an increase in the thrust for a limited body size. Although, most rotor arrangements cause rotor flow interaction, which degrade the total thrust. To design a rotor arrangement on small multirotor UAVs, it is necessary to first evaluate the thrust from an aerodynamic perspective. In this study, we evaluated the effect of rotor flow interactions on thrust for three two-rotor configurations. The investigation showed that the thrust of rotors in wake flow is degraded. Thus, we proposed a new octorotor UAV configuration based on the results of our evaluation of the rotor flow interaction and verified the thrust improvement compared to a coaxial octorotor UAV configuration. This investigation demonstrated a thrust improvement of 24% over the total thrust of the coaxial octorotor UAV.

When an active volcano erupts, a restricted area is typically set according to the eruption level. However, it is very important to observe eruption products inside of this area to predict the timing and scale of volcanic hazards, such as debris flows. Therefore, we propose a robotic observation system for active volcanoes that is composed of a multi-rotor unmanned aerial vehicle (UAV) and a mobile ground robot. To deliver the ground robot safely from the multi-rotor UAV to the ground, we implemented a sky-crane mechanism and confirmed the feasibility of the mechanism theoretically. In this paper, we introduce our volcano observation scenario as well as the observation system and sky-crane mechanism we have developed. Finally, we report on a field test conducted at Mount Asama in September 2013.

During a volcanic activity, it is very dangerous to approach a restricted area. For this reason, robotic remote observation system would be quite useful, and it is particularly urgent for a country with a high degree of volcanic activity, such as Japan. In response to this need, our research group developed a novel multi-D.O.F. tracked vehicle, called ELF, which can conduct observation in a restricted volcanic area. The robot essentially consists of six tracks, and it has eleven actuators that change its configuration. These actuators enable the robot to assume various configurations, which increase its ability to traverse weak and rough terrains in the area around a volcano. In this research, we propose one configuration of the robot, in which the surface of the contact plane at the bottom of the track is horizontal, which is advantageous for traversing a weak slope. The feasibility of this design was verified in a field experiment on Mt. Kushigata, on the island of Izu-Oshima, and in a simulated volcanic field that was filled with pumice stones.

Rovers that are used to explore craters on the Moon or Mars require the mobility to negotiate sandy slopes, on which slippage can easily occur. Such slippage can be reduced by actively readjusting the attitude of the rovers. By changing attitude, rovers can modify the position of their center of gravity and the wheel-soil contact angle. In this study, we discuss the effects of attitude changes on downhill sideslip based on the slope failure mechanism and experiments on reconfiguring the rover attitude and wheel angles. We conducted slope-traversing experiments using a wheeled rover under various roll angles and wheel angles. The experimental results show that the contact angle between wheels and slopes has a dominant influence on sideslip when compared with that of readjusting the rover's center of gravity.

The surfaces of both the Moon and Mars are covered with loose soil, with numerous steep slopes along their crater rims. Therefore, one of the most important requirements imposed on planetary rovers is their ability to minimize slippage while climbing steep slopes, i.e., the ability to generate a drawbar pull with only a small amount of slippage. To this end, the wheels/tracks of planetary rovers typically have parallel fins called lugs (i.e., grousers) on their surface. Recent studies have reported that these lugs can substantially improve the traveling performances of planetary rovers. Therefore, in this study, we conducted experiments using lightweight two-wheeled and mono-tracked rovers to provide a quantitative confirmation regarding the influence of lugs on the traveling performances of planetary rovers. Based on our experimental results, we confirmed that, although an increase in the number of lugs contributes to the high traveling performance of wheeled rovers, it does not contribute much to that of tracked rovers. Furthermore, an increase in lug height improves the traveling performances of both types of rovers.

Future planetary rovers are expected to probe over steep sandy slopes, such as crater rims, where wheel slippage can be a critical issue. One solution to this issue is to mount redundant actuators on the locomotion mechanisms of the rovers such that they can actively reconfigurate themselves to adapt to the driven terrain. In this study, we propose a mechanical model of a rover based on a wheel-soil contact model combined with the classical terramechanic theory. The effects of the rover reconfiguration on its slippage tendencies are analyzed based on slope traversing experiments and numerical simulations. The validation of the proposed contact model is also discussed based on experimental and numerical simulation results. According to the experimental results, both longitudinal and lateral slippages are greatly reduced by tilting the rover in an uphill direction. The results of the numerical simulation match the experimental results quantitatively, and indicate the possible need to include a slope failure model.

This paper proposes a novel control strategy for autonomous underwater vehicles (AUVs), named as path tracking, which combines the conventional path following and trajectory tracking control in order to achieve smooth spatial convergence and tight temporal performance as well. This idea is inspired by the previous work of Hindman [1] and Encarnacao [2], however, the path tracking design herein goes from path following to trajectory tracking, which indeed is an inverse way from the previous solutions so that the complex projection algorithm resulting in a local stability is avoided. A kinematics controller is first derived by using Lyapunov direct method where a virtual path parameter is introduced to bring an extra control degree of freedom, and then it is extended to the dynamics of AUVs based on backstepping technique. The resulting nonlinear control design is formally shown and it yields global asymptotic convergence of the AUV to the path. Finally, simulation results illustrate the efficiency of the path tracking control design for AUVs.

Numerical simulation analysis of the motion of wheeled mobile robots is significant for both their R&D and control phases, especially due to the recent increase in the number of planetary exploration missions. Using the position/orientation of the rover body and all the joint angles as generalized coordinates, the Jacobian matrices and recursive dynamic models are derived. Terramechanics models for calculating the forces and moments that act on the wheel-as a result of the deformable soil-are introduced in consideration of the effect of normal force. A rough terrain modeling method is developed for estimating the wheel-soil interaction area, wheel sinkage, and the terminal coordinate. A simulation program that includes the above techniques is developed using Matlab and SpaceDyn Toolbox. Experimental results from a 4-wheeled mobile robot moving on Toyoura soft sand are used to verify the fidelity of the simulation. A simulation example of a robot moving on a random rough terrain is also presented.

This paper provides valuable information about 3-D map construction using a tracked vehicle at Disaster City. Disaster City is a training facility for the Federal Emergency Management Agency (FEMA) in the United States. FEMA staff used our rescue robot Kenaf to conduct simulated emergency testing. Kenaf is a tele-operated tracked vehicle that has high mobility suitable for use in outside terrains and inside buildings. We equipped Kenaf with a 3-D laser scanner that can measure dense and wide angle 3-D shapes. We collected about 50 3-D mapping data sets during the tests. A part of these data sets can be accessed at our website. In this paper, we explain the Kenaf's tele-operation system, the 3-D mapping system, and the comments about the usability of the 3-D mapping from FEMA staff. In addition, we discuss about the limit of our mapping method on the basis of the trials at Disaster City. This information will be helpful for researchers in the robotics to improve their method of 3-D map construction and their tracked vehicles.

This paper describes the development of a sensing device that can be used to estimate the position of mobile robots on slippery terrains. The device consists of an optical sensor designed for a computer mouse and dual laser light sources for generating a laser speckle pattern. It detects the motion of a moving surface at a large distance from the surface, from 80 mm to 300 mm, by tracking the laser speckle pattern. The use of dual laser light sources makes the tracking robust for both large distances from the ground and different surface materials. Some fundamental experiments validated the performance of the device, which tracked surfaces of different materials with high accuracy under various height conditions. Finally, the device was mounted on our mobile robot, and simple experiments were conducted on a slippery sandy terrain to evaluate the usefulness of the device as a noncontact odometry system.

In the case of disasters such as earthquakes or Nuclear/Biological/Chemical(NBC) terrorist attacks, mobile robots, called “rescue robots,” that can work in dangerous environments instead of rescue crews in rescue missions, can be of great help. However, realizing such robot systems requires many types of technologies. In particular, path planning is an important technology that provides a mobile robot with autonomous navigation to a target destination with collision avoidance. To avoid evacuees, the robot should consider the motion of people in the near future. In this research, we propose a collision avoidance method that estimates the motions and personal spaces of the evacuees. The method consists of three steps: “estimation,” “conversion,” and “planning.” In the estimation step, the future positions of evacuees are estimated by considering their planned motions and personal spaces. Then, in the conversion step, a time axis is added to construct a 3D time-space coordinate system. Finally, in the planning step, a distance-time transform is applied to plan a safe 3D path from the robot's current position to the desired goal. The proposed method has been implemented on our rescue robot simulator, and some simulation experiments were conducted to verify its usefulness.

Tracked vehicles are frequently used as search-and-rescue robots for exploring disaster areas. To enhance their traversability on rough terrain, some are equipped with “active flippers.” However, manual control of such flippers also increases the operator's workload, particularly for teleoperation with limited camera views. To eliminate this tradeoff, we developed a shared autonomy system using an autonomous controller for flippers that is based on continuous three-dimensional terrain scanning. In our system, real-time terrain slices near the robot are obtained using three laser range sensors, and these are integrated to generate three-dimensional terrain information. In this paper, we introduce the autonomous controller for the flippers and validate the reliability of the shared autonomy system through experimental results on actual rough terrain.

This paper describes various configurations of two connected unit crawlers. By changing the relative position of the two connected vehicle units, the overall robot comprising such a mechanism can automatically adapt to surface obstacles on the field, including complicated structures such as disaster-generated debris. In addition, we analyzed the effect of axis arrangements in order to simplify the realization of the switching function so as to achieve the four basic configurations.

In this paper, a new category of the wheel-leg hybrid robot is presented. The proposed mechanism can compose large wheel diameter compared with the previous hybrid robot to realize a greater ability to climb obstacles. A prototype model of one Wheel-Leg module of the proposed robot mechanism has been developed to illustrate the concept. Actual design and mode changing experiment with a test mechanical module is also presented. Basic movement tests and a test of the basic properties of the rotational fingertip are also shown. The Basic configurations of wheel-leg retractable is considered well. The integrated mode is also described.

In this video, a novel tracked mechanism for sideways motion is presented. The tracked mechanism is of circular cross-section and has active rolling axes at the center of the circles. Conventional tracked mechanisms can support massive loads, but cannot produce sideways motion. Additionally, previous crawler edges sink undesirably on soft ground, particularly when the vehicle body is subject to a sideways tilt. The proposed design solves these drawbacks by adopting a circular cross-section crawler. A prototype has been developed to illustrate the concept. Motion experiments confirm the novel properties of this mechanism: sideways motion and robustness against edge-sink. Motion experiments, with a test vehicle are also presented.

The wheel slip ratio is an important state variable in terramechanics research and the control of planetary rovers. Definitions of the slip ratio for a wheel with lugs and methods of estimating it for all wheels onboard have seldom been attempted. This paper presents several definitions for the slip ratio of a lugged wheel, which can be interconverted by altering the shearing radius. Equations for calculating the longitudinal velocity and slip ratio of a wheel moving on rough terrain are deduced from the horizontal speed of the wheel's axle. Wheel-soil interaction experiments were performed for two types of wheels with different radii and lugs of different heights. The drawbar pull, torque, and wheel sinkage were measured using sensors. These data confirmed the effectiveness of the proposed slip ratio definition methods. Furthermore, two slip ratio estimation methods are proposed and verified: a visual information-based method by analyzing the lug traces marked on the terrain with high precision, and a terramechanics-based method in which the equations for the vertical load and torque are solved to estimate the slip ratios of all wheels.

Identifying planetary soil parameters is not only an important scientific goal, but also necessary for exploration rover to optimize its control strategy and realize high-fidelity simulation. An improved wheel-soil interaction mechanics model is introduced, and it is then simplified by linearizing the normal stress and shearing stress to derive closed-form analytical equations. Eight unknown soil parameters are divided into three groups. The highly complicated coupled equations, each of which includes all the unknown soil parameters, are then decoupled. Each decoupled equation contains one or two groups of soil parameters, making it feasible to make a step-by-step identification of all the unknown parameters that characterize the soil. Wheel-soil interaction experiments were performed for six kinds of wheels with different dimensions and wheel lugs on simulated planetary soil. Soil parameters are identified with the measured data to validate the method, which are then used to predict wheel-soil interaction forces and torque, with a less than 10% margin of error. The improved model, decoupled analytical model, and soil-characterizing method can play important roles in the development of both the planetary exploration rovers and the terrestrial vehicles.

The wheels of planetary rovers that are used in space explorations sometimes slip or lose contact with the ground while traversing a sandy terrain. In order to estimate the behavior of these rovers moving on loose soil, it is very important to accurately estimate the drawbar pull of their wheels. Some wheel-soil interaction models based on terramechanics have been proposed for the estimation of the normal stress distribution and drawbar pull of such rovers. However, our experimental results (normal stress distributions are directly measured using a pressure sensor array, which is attached to the wheels of a rover) show that the distribution range of normal stress for small wheeled rovers obtained using the proposed method is considerably smaller than that obtained by using conventional method. Consequently, the drawbar pull estimated using conventional methods is inaccurate. Therefore, in this study, the normal stress distribution is directly measured using pressure sensors in order to estimate drawbar pull accurately. From the data obtained using the sensors, a soil parameter, which is generally very difficult to measure, is estimated. Then, the drawbar pull is estimated using this parameter. The drawbar pull estimated by using the proposed method is more accurate than that estimated using conventional methods. In this study, we propose a new method for the estimation of drawbar pull and also validate this method.

For tracked vehicles moving over rough terrain, it is important to avoid rollovers and rapid motion. To realize smooth locomotion on rough terrain, some tracked vehicles are equipped with ¿active flippers.¿ Such flippers increase the traversability and stability of tracked vehicles. However, their control increases the operator workload, especially in the case of teleoperation. To eliminate this problem, we have developed an autonomous controller for generating terrain-reflective motions of flippers. Terrain information is obtained using laser range sensors that are located at both sides of our tracked vehicle testbed. Using this system, operators only have to specify a direction to the robot, following which the robot traverses rough terrain using autonomous flipper motions. In this paper, we introduce a strategy and an algorithm for the controller for active flippers and validate the reliability of the system through experimental results on rough terrain.

In this paper, a tetrahedral mobile robot with central axis for transformation to the flat vehicle is presented. The throwable robot with the function of going into narrow spaces when its in the flat-vehicle mode is explained in detail. A prototype has been developed to illustrate the concept. Motion experiments confirm the novel properties of this mechanism: mode changing function and omnidirectional motion. Basic Motion experiments, with a test vehicle are also presented.

In this paper, the basic running performance of the cylindrical tracked vehicle with sideways mobility is presented. The crawler mechanism is of circular cross-section and has active rolling axes at the center of the circles. Conventional crawler mechanisms can support massive loads, but cannot produce sideways motion. Additionally, previous crawler edges sink undesirably on soft ground, particularly when the vehicle body is subject to a sideways tilt. The proposed design solves these drawbacks by adopting a circular cross-section crawler. A prototype. Basic motion experiments with confirm the novel properties of this mechanism: sideways motion and robustness against edge-sink.

This paper presents slope traversal experiments with slip compensation control for lunar/planetary exploration rovers. On loose soil, wheels of the rover easily slip even when the rover travels with relatively low velocity. Because of the slip, following an arbitrary path on loose soil becomes a difficult task for the rover, and also, the slip will increase when the rover traverses a slope. To cope with the slip issue, the authors previously proposed path following control strategy taking wheel slippages into account. Through numerical simulations in the previous work, it has been confirmed that the proposed control effectively compensates and reduces the slip motions of the rover, and then, the rover can follow a given path. In order to confirm the usefulness of the proposed control for practical application, slope traversal experiments using a four-wheeled rover test bed are addressed in this paper. The control performance of the slip compensation is compared to that of no slip control based on motion traces of the rover in side slope traversal case. Further, the effectiveness of the proposed control is verified by quantitative evaluations of distance and orientation errors.

For a mobile robot it is critical to detect and compensate for slippage, especially when driving in rough terrain environments. Due to its highly unpredictable nature, drift largely affects the accuracy of localization and control systems, even leading, in extreme cases, to the danger of vehicle entrapment with consequent mission failure. This paper presents a novel method for lateral slip estimation based on visually observing the trace produced by the wheels of the robot, during traverse of soft, deformable terrain, as that expected for lunar and planetary rovers. The proposed algorithm uses a robust Hough transform enhanced by fuzzy reasoning to estimate the angle of inclination of the wheel trace with respect to the vehicle reference frame. Any deviation of the wheel trace from the planned path of the robot suggests occurrence of sideslip that can be detected, and more interestingly, measured. This allows one to estimate the actual heading angle of the robot, usually referred to as the slip angle. The details of the various steps of the visual algorithm are presented and the results of experimental tests performed in the field with an all-terrain rover are shown, proving the method to be effective and robust.

In this paper, a trafficability analysis for the exploration rover is described. A rover traveling on loose terrain often experiences its slippages (wheel slips or vehicle sideslip), and in particular, these slips become larger when the rover traverses on sandy slopes. The authors have investigated traction mechanics of a rigid wheel of the rover on loose terrain with paying attention to slipping behaviors of the wheel. In this paper, based on our previous works regarding the wheel-terrain mechanics, we propose a Thrust-Cornering Characteristic Diagram for trafficability analyses of the rover. The thrust-cornering characteristic diagram consists of various characteristics curves of wheel forces, namely thrust and cornering forces, with various wheel slippage conditions. This diagram provides quantitative criteria for slope traversing capability of the rover on arbitrary angles of slope. The usefulness of the proposed diagram for the trafficability analysis is confirmed through slope traversal experiments using a four-wheel test bed. Further, a steering maneuver control for slope traversing situation is discussed based on the diagram.

Active flippers for tracked vehicles are very useful to improve traversability on uneven terrain. However it is widely known that control of flippers also increases the work-load for operators, particularly where the vehicle and the operator are far apart. To reduce the work-load, we aim to realize a sensor-based autonomous controller of flippers to enable a “semi-autonomous operation” of tracked vehicles. The “semi-autonomous operation” means that the only requirement for an operator is to indicate the robot’s direction. In this way, the robot is navigated autonomously through its sensors and actuators to surmount or avoid obstacles. In this research, two laser range sensors are used for terrain sensing, and gyro sensors are used for the measurement of the robot’s attitude. Based on such sensor system, we propose a strategy of simple sensor-based motion of active flippers for tracked vehicles to enable a semi-autonomous operation. In this paper, we introduce a strategy of motion of active flippers, and the stability analysis of tracked vehicles with active flippers. Finally, we report several experimental results to verify the validity of our approach.

Active flippers for tracked vehicles are very useful to improve traversability on uneven terrain. However it is widely known that control of flippers also increases the work-load for operators, particularly where the vehicle and the operator are far apart. To reduce the work-load, we aim to realize a sensor-based autonomous controller of flippers to enable a ‘semi-autonomous operation’ of tracked vehicles. In this research, two laser range sensors are used for terrain sensing, and gyro sensors are used for the measurement of the robot’s attitude. Based on such sensor system, we propose a strategy of simple sensor-based motion of active flippers for tracked vehicles to enable a semi-autonomous operation. In this paper, we introduce a strategy of motion of active flippers. Finally, we report several experimental results to verify the validity of our approach.

In this paper, we propose an action planning algorithm and its evaluation method based on dynamic simulation for a novel type of hybrid leg-wheel rover for planetary exploration. Hybrid leg-wheel robots are recently receiving a growing interest from the space community to explore planets, since they offer an appropriate solution to gain improved speed and mobility on unstructured terrain. However, in order to fully reach the hybrid mechanismpsilas potential, it is necessary to establish an optimal way to define when to use one over the other locomotion mode, depending on the soil conditions and topology. Even though this step is crucial, little attention has been devoted to this topic by the robotic community. The switching of motion mode, that is either wheel or leg are the actions to be planned, that we are considering in this paper. We aim at generating the safest and the least energy demanding path to reach a point of scientific interest. In order to define the optimal path with the set of switching actions required for the robot to follow it, the authors developed an action planning algorithm and a path evaluation method based on a four steps approach. First, an optimal candidate path on a rough terrain is generated based on topology and specificationspsila criteria functions. Then switching actions are defined along this path depending on the hybrid robotpsilas performances in each motion mode. The next step is a dynamic simulation of the robot controlled to follow the path. Finally, the path is evaluated based on the energy profile spent by the actuators and calculated by the simulation. Demonstrations for the proposed technique are addressed along with a discussion on characteristics of the candidate path and the energy profile of the robot.

In this paper, a novel crawler mechanism for sideways motion is presented. The crawler mechanism is of circular cross-section and has active rolling axes at the center of the circles. Conventional crawler mechanisms can support massive loads, but cannot produce sideways motion. Additionally, previous crawler edges sink undesirably on soft ground, particularly when the vehicle body is subject to a sideways tilt. The proposed design solves these drawbacks by adopting a circular cross-section crawler. A prototype has been developed to illustrate the concept. Motion experiments confirm the novel properties of this mechanism: sideways motion and robustness against edge-sink. Motion experiments, with a test vehicle are also presented.

In this paper, a path planning and its evaluation method is described with taking into account wheel slip dynamics of lunar/planetary exploration rovers. The surface of the planetary body is largely covered with powdery soil. On such loose soil, the wheel slippage which will make the rover get stuck must be concerned. Since the slippage dynamically depends on the posture/velocity of vehicle, soil characteristics, and wheel-soil interactions, it becomes difficult issues to incorporate the wheel slip dynamics as a criterion into path-planning algorithms. To tackle the slippage problem, the authors develop the path-planning algorithm and the path-evaluation method based on the following approach. First, a path on a rough terrain is generated with the terrain-based criteria function. Subsequently, the dynamics simulation of a rover is carried out in which the rover is controlled to follow the candidate path. Finally, the path is properly evaluated based on the slip motion profiles calculated by the simulation. Demonstrations for the proposed technique are addressed along with a discussion on characteristics of the candidate path and the slip motion profile of the rover

Crawler mechanisms have the advantage of stable navigation on uneven terrain; as a result, such mechanisms have been adopted for many types of locomotion of outdoor robots, including "search and rescue robots". However, crawler mechanisms always slip when tracking curved paths, and it generates a large accumulating positioning error in vehicles as opposed to conventional wheeled mobile robots. To measure the velocity of the vehicle correctly and improve the accuracy of the odometry, consideration of crawlers' slippage is very important. In this research, we propose a more accurate odometry method for crawler vehicles. In the proposed method, the vehicle can estimate the slip ratios using information from encoders (attached to the actuators) and gyro-sensors. The validity of the method was confirmed by experiments using our crawler vehicle.

Tracked vehicles have the advantage of stable locomotion on uneven terrain, and, as a result, such mechanisms are used for locomotion on outdoor robots, including those used for search and rescue. However, such mechanisms always slip when a tracked vehicle follows a curve, and the slippage generates large accumulated positioning errors in the vehicle compared with conventional wheeled mobile robots. To improve the accuracy of the odometry and enable a path-following control, the estimation of the track slippage is essential. In this paper, we propose an improved method of odometry for tracked vehicles to follow a straight line or a curve. In this method, the vehicle estimates the slip ratios using two encoders (attached to the actuators) and a gyro-sensor. Based on the improved odometry, the path-following control of tracked vehicles is significantly improved. The validity of the method was confirmed with experiments involving our tracked vehicle on several types of surfaces.

In this paper, a path following control strategy for lunar/planetary exploration rovers is described, taking into account slip motion of the rover. It is determined that the slip motion of each wheel of the rover must be increased and cannot be neglected when the rover travels on loose soil. Because of slip, following an arbitrary path on loose soil is a difficult task. In order to improve this situation, the authors have developed a path following algorithm with slip compensation. In this algorithm, both steering and driving maneuvers of the rover are derived not only to follow an arbitrary path, but also simultaneously compensate for the slip. The performance of the path following strategy is confirmed through numerical simulation using the wheel-and-vehicle model elaborated in our previous research. The slip motion of the wheel is also addressed, based on a terramechanics approach. The proposed path following algorithm shows better performance than traditional control without slip compensation in the simulation

In this paper the authors present the current progress of a networked robotic system intended to be deployed at disaster areas. This system is formed by three mobile robots: two twin crawlers that will have search-and-recognition tasks gathering information about their surroundings, and an outdoor-wheeled rover that will approach the area and which will also carry the two crawlers. The communication system for these robots consists of a wireless local area network that will have an operator located at a safe distance controlling them. As a final communication objective, the integration of a satellite-based IP communication, linked to the Japanese satellite ETS-VIII is scheduled. In order to be able to navigate the crawlers remotely, a wireless LAN camera and a Laser Range Finder (LRF) sensor have been mounted on both of the crawlers. These LRFs will scan the area where the crawler is at, obtaining a detailed point-based 3D image. A special focus of this paper is made on the possibility of maneuvering the crawlers based only on the remotely-acquired LRF and camera's information.

When a mobile robot executes a given task in human-robot co-existence environment, it is necessary for the robot to perform robust motions and to have abilities to deal with unforeseen situations. Therefore we aim to realize an intelligent and robust motion for a dual-arm mobile manipulator. To carry out a research of intelligent motion, we set a concrete task as "grasping a book and returning it to a bookshelf". In this task, a path of an end-effector that grasps a book should be planned according to the book's position. A motion of returning a book also requires confirming return position and planning manipulator's motion. In this paper, we introduce our motion planning algorithm for a dual-arm mobile manipulator, and shows an example of integrated motion of "tidying a room" task.

In the fields of urban search and rescue (USAR), it is important that crawler-type mobile robots explore occluded areas (collapsed buildings, underground shopping centers, etc.) in preference to rescue workers from the point of view of safety. To map such an occluded environment, it is important for robots to localize their position and pose. In this paper, we propose two three-dimensional localization algorithms for crawler-type mobile robots. The algorithm is based on "three-dimensional scan-matching" using the three-dimensional laser range finder information. Several experiments using our crawler-type mobile robot verifies the validity and limitation of this method in a simulated disaster environment.

To relieve damages of earthquake disaster, "The Special Project for Earthquake Disaster Mitigation in Urban Areas" have been kicked off in Japan. Our research group is a part of the sub-project "modeling of disaster environment for search and rescue" since 2002. In this project, our group aims to develop a three-dimensional mapping's algorithm that is installed in a mobile robot to search victims in a collapsed building. To realize this mission, it is important to map environment information, and also the mapping requires localization simultaneously. (This is called "SLAM problem".) In this research, we use three-dimensional map by laser range finder, and we also estimate its location in a global map using correlation technique. In this paper, we introduce our localization and mapping method, and we report a result of preparatory experiment for localization.

This paper describes a new method for improving the azimuth accuracy of range information using conventional (Polaroid) low-resolution ultrasonic sensors mounted in a circular array on a mobile robot. Although ultrasonic sensors are fairly accurate in measuring distance in depth, they commonly have significant uncertainty in azimuth. We model this uncertainty with a uniform distribution along an arc. This means that the echo has an equal likelihood of originating from any point along the arc. We then introduce a new method to fuse sonar data to better approximate the actual obstacle location. This new method is termed the arc transversal median method because the robot determines the location of an object 1) by intersecting one arc with other arcs, 2) then by considering only "transversal" intersections, those which exceed a threshold in angle, and 3) by taking the median of the intersections. The median is a robust estimator that is insensitive to noise; a few stray readings will not affect its value. We show, via some simple geometric relationships, that this method can improve the azimuth accuracy of the sonar sensor by a specified amount under well-defined conditions. Experimental results on an ultrasonic sensor array situated on a mobile robot verify this approach.

Our research goal is to realize a motion planning for an intelligent mobile manipulator. To plan a mobile manipulator's motion, it is popular that the base robot motion is regarded as manipulator's extra joints, and the whole system is considered as a redundant manipulator. In this case, the locomotion controller is a part of the manipulator controller. However, it is difficult to implement both controllers as one controller, in our implementation experience, because of difference of actuators' character. In this research, we focus on a path planning algorithm for a mobile base with keeping manipulability at the tip of the mounted manipulator. In this case, the locomotion controller is independent from the manipulator controller, and a cooperative motion is realized by a communication between both controllers. In this paper, we propose a motion planning algorithm for a mobile manipulator, and report several experimental results.

Our research objective is to realize sensor based navigation by car-like mobile robots. The generalized Voronoi graph (GVG) can describe a mobile robot's path for sensor based navigation from the point of view of completeness and safety. However, it is impossible to apply the path to a car-like mobile robot directly, because limitation of the minimum turning radius prevents following the non-smooth GVG. To solve the problem, we propose a local smooth path planning algorithm for car-like mobile robots. Basically, an initial path is generated by a conventional path planning algorithm using GVG theory, and it is deformed smoothly to enable car-like robots' following by maximizing an evaluation function proposed in the paper. The key topics are: definition of our evaluation function; and how to modify the GVG. We introduce a local smooth path planning algorithm based on the GVG, and explain a detail of the evaluation function. Simulation results support validity of the algorithm.

This paper presents a new method for simultaneous localization and mapping that exploits the topology of the robot's free space to localize the robot on a partially constructed map. The topology of the environment is encoded in a topological map; the particular topological map used in this paper is the generalized Voronoi graph (GVG), which also encodes some metric information about the robot's environment, as well. In this paper, we present the low-level control laws that generate the GVG edges and nodes, thereby allowing for exploration of an unknown space. With these prescribed control laws, the GVG can be viewed as an arbitrator for a hybrid control system that determines when to invoke a particular low-level controller from a set of controllers all working toward the high-level capability of mobile robot exploration. The main contribution, however, is using the graph structure of the GVG, via a graph matching process, to localize the robot. Experimental results verify the described work.

Our research goal is to realize a robust navigation in indoor and outdoor environment for autonomous vehicle. An omnidirectional vehicle driven by four Mecanum wheels was chosen for our research platform. Mecanum wheel has 16 tilted rollers (45 degrees against the direction of wheel rotation) around the wheel, so the vehicle moves omnidirectionally by controlling these wheels independently. However, it has a disadvantage in odometry because of wheel slippage. Particularly, when the robot moves laterally, same wheels' rotations generate different traveling distance depending on friction of ground surface. To cope with the problem, we estimate robot's position by detecting optical flow of ground image using vision sensor (visual dead-reckoning). The estimation method is inaccurate comparing with odometry, but it is independent from friction of ground surface. Therefore, the estimated vehicle position can be improved by fusing odometry and visual dead-reckoning based on maximum likelihood technique. This paper describes an odometry method and a visual dead-reckoning method for omnidirectional vehicle, and fusion technique to improve the estimated position of the vehicle. Finally, experimental results support above technique.

This paper describes a new method for determining range information about a robot's surroundings using low resolution ultrasonic sensors. These sensors emit ultrasound which bounces off of nearby objects and returns to the sensor. The time-of-flight for the sound to return to the sensor is the distance between the sensor and the object. A sonar arc represents the possible locations of the object. We model these locations with a simple uniform probability distribution on the sonar arc. We then introduce a new method to fuse sonar data to determine the actual obstacle location. This new method is termed the arc-transversal median method because the robot determines the location of an object by intersecting one arc with other arcs whose angle-of-intersection exceeds a threshold and then taking the median of the intersection. The median is a robust estimator that is insensitive to noise because a few stray readings will not affect the median. We show via some simple geometric relationships, that this method can improve the accuracy of the sonar sensor by a specified amount, when certain assumptions were in place. Finally, experimental results on a real mobile robot verify this approach.

Considers sensor based mobile robot exploration in an unknown indoor environment. One of the big problems in this area is positioning error. To deal with this problem in the exploration task, we proposed a localization method using a partially constructed topological map termed the generalized Voronoi graph (GVG). The GVG-based method performed successfully in some large scale indoor environments, but had problems resulting from poor sensing ability of the sixteen sonar sensors on-board the robot. The poor sensing ability was particularly deleterious at geometric structures in the GVG that were "unstable." To solve the problem, we adopted "the Reduced Generalized Voronoi Graph (RGVG)" for the exploration map instead of the original GVG. The RGVG is a stable subset of the GVG and is sufficient for motion planning. To enable realistic and reliable exploration using the RGVG structure, we developed an edge matching procedure for topology matching. In this paper, we introduce the RGVG structure and the edge matching procedure for robust exploration. Experimental results verify the described work.

Sensor based exploration is a task which enables a robot to explore and map an unknown environment, using sensor information. The map used in this paper is the generalized Voronoi graph (GVG). The robot explores an unknown environment using an already developed incremental construction procedure to generate the GVG using sensor information. This paper presents some initial results which uses the GVG for robot localization, while mitigating the need to update encoder values. Experimental results verify the described work.

A goal of this research is to successfully accomplish a long distance navigation task, including "passing through a doorway", by an autonomous robot equipped with a manipulator. In our approach to this problem, we apply the concept of action primitives to the mobile manipulator control system. Action primitives are defined as unit elements of a complex behavior, such as door opening behavior. Basically, the action primitives control a robot according sequences of planned motion primitives. But as an important feature, each action primitive is designed with an error adjustment mechanism to cope with accumulated positioning error of the mobile base. In this paper, we report the design and implementation of action primitives for door opening behavior for our experimental robot, and show experimental results of an autonomous mobile manipulator's "passing through a doorway" using sequences of designed action primitives.

An aim of this research is to realize a behavior of opening a door and passing through a door-way using an autonomous mobile robot equipped with a manipulator. This behavior is realized by integrating several sub-tasks, such as, finding a door knob, pushing the door to open by cooperation between a manipulator and a locomotion. First, we pay attention to one important sub-task, pushing the door. To realize the sub-task, a mobile robot needs to cooperate with an equipped manipulator. In this paper, we propose how to implement the sub-task on the robot, and show experimental results of it.

One approach of how to pass through a doorway by a mobile robot is discussed. In this task-oriented approach, the proposed task is to realize a total behavior of opening a door and passing through a doorway for a mobile robot equipped with a manipulator. In this paper, we describe a design of such behavior, and a simulation of the behavior is shown. The key of such behavior is the cooperation between robot's function sub-systems, e.g. the locomotion control system, the manipulator control system and the sensor systems.>

A path planning algorithm for mobile robotics is proposed. When a mobile robot is navigating, the error in estimated position of the robot increases in proportion to the traveling distance. Because of this error, the robot has a greater risk of collision with objects in the environment. To reduce this error, a robot should obtain environmental information by using its environment sensors, and modify its estimated position accordingly. The authors propose a cost function for the mobile robot's path which minimizes the risk of collision and an algorithm to find the optimal path and sensing points. They have implemented the proposed algorithm on a real robot system and conducted several experiments to verify it.