Modular robotics holds immense potential for space exploration, where reliability, repairability, and reusability are critical for cost-effective missions. Coordination between heterogeneous units is paramount for precision tasks - whether in manipulation, legged locomotion, or multi-robot interaction. Such modular systems introduce challenges far exceeding those in monolithic robot architectures. This study presents a robust method for synchronizing the trajectories of multiple heterogeneous actuators, adapting dynamically to system variations with minimal system knowledge. This design makes it inherently robot-agnostic, thus highly suited for modularity. To ensure smooth trajectory adherence, the multidimensional state is constrained within a hypersphere representing the allowable deviation. The distance metric can be adapted hence, depending on the task and system under control, deformation of the constraint region is possible. This approach is compatible with a wide range of robotic platforms and serves as a core interface for Motion Stack, our new open-source universal framework for limb coordination (available at https://github.com/2lian/Motion-Stack). The method is validated by synchronizing the end-effectors of six highly heterogeneous robotic limbs, evaluating both trajectory adherence and recovery from significant external disturbances.

Developing algorithms for extra-terrestrial robotic exploration has always been challenging. Along with the complexity associated with these environments, one of the main issues remains the evaluation of said algorithms. With the regained interest in lunar exploration, there is also a demand for quality simulators that will enable the development of lunar robots. In this paper, we propose Omniverse Lunar Robotic-Sim (OmniLRS) that is a photorealistic Lunar simulator based on Nvidia’s robotic simulator. This simulation provides fast procedural environment generation, multi-robot capabilities, along with synthetic data pipeline for machine-learning applications. It comes with ROS1 and ROS2 bindings to control not only the robots, but also the environments. This work also performs sim-to-real rock instance segmentation to show the effectiveness of our simulator for image-based perception. Trained on our synthetic data, a yolov8 model achieves performance close to a model trained on real-world data, with 5% performance gap. When finetuned with real data, the model achieves 14% higher average precision than the model trained on real-world data, demonstrating our simulator’s photorealism. The code is fully open-source, accessible here: https://github.com/AntoineRichard/OmniLRS, and comes with demonstrations.

The ability to associate the current location with previously visited places is an essential aspect of autonomous ground robots. Unstructured environments such as planetary surfaces pose a significant challenge for robots because their terrain is less distinctive. Meanwhile, traversability must be analyzed simultaneously for safe navigation. In the past, place recognition research has rarely considered traversability analysis despite its significance. This is because the structural information of terrains becomes quickly implicit during the encoding process. This paper provides a method that explicitly addresses both problems: place recognition and traversability analysis. It proposes a discrete Fourier transform (DFT) to represent the frequency components embedded in ground curvature, which underlies both concepts. Our place recognition function demonstrates excellent performance in extensive experiments using challenging planetary & urban datasets while estimating traversability that other approaches find difficult to handle.

This paper introduces CloverNet, a novel convolutional neural network (CNN) designed for real-time semantic segmentation capabilities onboard planetary exploration rovers. Teleoperating planetary rovers is a tedious task as it requires close to real-time monitoring and planning, while distance and communication delay further cripple the efficiency. Future up-scaling of off-world robotic systems deployment makes it increasingly difficult to monitor and command each agent in real-time. Thus, at least an autonomous maneuvering capability is essential to reduce the operational workload at the ground station. In order to achieve this objective, the rover is required to understand its operational environment. The rover then needs to process the information at real-time and efficiently respond in order to complete the allocated tasks or to recover from hazards. An innovative CNN for real-time semantic segmentation is proposed, which can be run on limited memory and graphics processing unit (GPU). The solution is benchmarked on an RGB-D visual sensor and on an NVIDIA Jetson AGX Xavier mounted on a skid-steering micro-rover platform. CloverNet consists of a light encoder-decoder architecture that is optimized and quantized using the NVIDIA TensorRT framework, enabling it to operate at high frame rate and low GPU latency. The network is trained using a new data set curated for developing semantic segmentation of rocks and rovers belonging to Lunar and Martian analogue environments. Experimental results showed it can reach high performance in terms of accuracy and intersection over the union, as well as achieving a maximum inference speed of ∼ 55 FPS on a GPU board at the edge. As such, the results prove CloverNet suitable for planetary missions.

Robotic mobility in microgravity is necessary to expand human utilization and exploration of outer space. Bio-inspired multi-legged robots are a possible solution for safe and precise locomotion. However, a dynamic motion of a robot in microgravity can lead to failures due to gripper detachment caused by excessive motion reactions. We propose a novel Reaction-Aware Motion Planning (RAMP) to improve locomotion safety in microgravity, decreasing the risk of losing contact with the terrain surface by reducing the robot's momentum change. RAMP minimizes the swing momentum with a Low-Reaction Swing Trajectory (LRST) while distributing this momentum to the whole body, ensuring zero velocity for the supporting grippers and minimizing motion reactions. We verify the proposed approach with dynamic simulations indicating the capability of RAMP to generate a safe motion without detachment of the supporting grippers, resulting in the robot reaching its specified location. We further validate RAMP in experiments with an air-floating system, demonstrating a significant reduction in reaction forces and improved mobility in microgravity.

This paper presents the modeling and analysis of a novel moving mechanism "tumbling" for asteroid exploration. The system actuation is provided by an internal motor and torque wheel; elastic spring-mounted spikes are attached to the perimeter of a circular-shaped robot, protruding normal to the surface and distributed uniformly. Compared with the conventional motion mechanisms, this simple layout enhances the capability of the robot to traverse a diverse microgravity environment. Technical challenges involved in conventional moving mechanisms, such as uncertainty of moving direction and inability to traverse uneven asteroid surfaces, can now be solved. A tumbling locomotion approach demonstrates two beneficial characteristics in this environment. First, tumbling locomotion maintains contact between the rover spikes and the ground. This enables the robot to continually apply control adjustments to realize precise and controlled motion. Second, owing to the nature of the mechanical interaction of the spikes and potential uneven surface protrusions, the robot can traverse uneven surfaces. In this paper, we present the dynamics modeling of the robot and analyze the motion of the robot experimentally and via numerical simulations. The results of this study help establish a moving strategy to approach the desired locations on asteroid surfaces.

The commercial thermal infrared camera mounting the uncooled microbolometer array (UMBA), which detects thermal wavelengths from 8 to 14 μm, was modified for space use and applied to the small earth-observing satellite called Rising-2. The satellite was launched in 2014, and the camera successfully took 17 of the cloud top and 3 of the land images from the sun-synchronous orbit. Observed brightness temperatures based on the reference data acquired in the laboratory before the launch have been compared with verified products derived from the Japanese meteorological satellite called MTSAT-2, and we confirmed that the UMBA could sense brightness temperature distribution of the target. The demonstration of the commercial thermal infrared camera in orbit would innovate in the development of space instruments as a new approach.

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.

The surface of a minor body in space features a harsh terrain and microgravity. To explore such surfaces in detail, a robot with an appropriate moving mechanism is required. To this end, we proposed a robot that moves by gripping the surface like a rock climber. We focus on the robot's gait, where the motion of the idling arm generates the reaction force that acts on the gripper of the supporting arm. The reaction force needs to be controlled to maintain a grip without slipping. Therefore, we formulate a simultaneous control law that combines the tip position control of the idling arm with reactionless control by utilizing the reaction null-space. Moreover, the validity of the control law was confirmed by an experiment involving an air floating system under microgravity. Furthermore, a planar simulation clarified that the robot can move continuously on an irregular terrain.

Owing to the irregular terrain and microgravity environment of an asteroid, an appropriate locomotion mechanism is required for exploring the asteroid by a robot. In this paper, a ground grip locomotive robot is proposed. One of the most important requirements of the robot is the development of the finger gripping mechanism that can be attached on an uneven surface. To meet this requirement, grip condition and friction characteristics between the finger and the surface need to be understood. Therefore, we conducted an experimental evaluation of gripping characteristics by measuring the coefficients of friction between several types of fingers and simulated grounds. Moreover, the range of possible gripping angles for simulated ground was determined by conditional equations and confirmed by an experiment of gripping the ground using an air-floating system. In this paper, conical shape is shown to be effective for ground grip locomotive robot.

This paper addresses a dynamic model and a control method of a space robot with a rigid manipulator and a flexible appendage. The control method has been developed for performing multiple tasks: end-point motion control and vibration suppression control of a flexible appendage. A simple dynamic model that considers coupling between the manipulator and the flexible appendage is proposed for the control method. The tasks are performed simultaneously on the basis of their order of priorities using a redundant manipulator. Additionally, because vibration suppression requires feedback of the state of the flexible appendage, a state estimator of the appendage using a force/torque sensor is developed. Finally, the proposed model, control method, and state estimator were verified experimentally using an air-floating system.

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.

In this paper, we propose a new method of controlling a group of mobile robots based on formation abstraction. The shape of a formation is represented by a deformable polygon, which is constructed by bending a rectangle, to go through narrow spaces without colliding with obstacles. If the trajectory of the front end point, as well as the width and the length of the formation, are given, the formation automatically reshapes itself to fit the area through which the front part of the group has already safely passed. Furthermore, the robots continuously try to optimize their positions to decrease the risk of collisions by integrating a decentralized locational optimization algorithm into the formation control. We show that the objective function, taking into account the distance between robots, does not decrease for fixed and nonconvex polygonal formation shapes if the zero-order hold control is applied for a sufficiently short sampling period. We also analyze the influence of the decentralized locational optimization algorithm on the objective function in the case of variable formations. The effectiveness of the proposed method is demonstrated in both simulations and real robot experiments.

This paper discusses a vibration suppression control method for a space robot with a rigid manipulator and flexible appendage. A suitable dynamic model that considers the coupling between the manipulator and flexible appendage was developed for the controller to accomplish the vibration suppression control of the flexible appendage. The flexible appendage was modeled using a virtual joint model, and the control method was developed on the basis of this model. Although this type of control requires feedback of the flexible appendage state, its direct measurement is generally difficult. Thus, an estimator of the flexible appendage state was constructed using a force/torque sensor attached between the base and flexible appendage. The control method was experimentally verified using an air-floating system.

This paper presents the modeling and analysis of ciliary micro-hopping locomotion actuated by an eccentric motor, for enabling mobile robots to explore asteroids. Under the proposed system, elastic cilia are attached to the surface of the robot; this arrangement should enable the robot to have better mobility in a microgravity environment. However, in the development of the ciliary micro-hopping mechanism theoretical modeling and analysis of the interactive mechanics between the cilia and the environment pose technical challenges that need to be addressed. In this paper, we present the dynamics modeling of the ciliary micro-hopping locomotion actuated by an eccentric motor, along with its experimental validations and numerical simulations. The results of this study contribute to the design optimization of both the cilia mechanism and the motor control scheme.

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 presents the impedance-based contact control of a free-flying space robot utilizing a compliant wrist for non-cooperative satellite capture operation. An open loop impedance control law based on contact dynamics model is introduced to realize a desired coefficient of restitution defined between a manipulator hand of a space robot and a contact point on a free-flying target. The coefficient of restitution and the damping ratio are expressed as a function of contact and impedance parameters; and hence, the impedance parameters are tuned by setting a desired coefficient of restitution and a desired damping ratio. The collision experiment using twodimensional microgravity emulator, called air-floating test bed, verifies that the proposed open loop control law is capable of realizing a desired coefficient of restitution with fairly small errors.

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.

This study addresses a time-optimal control of a free-floating space robot to stabilize a tumbling target satellite while paying attention to: 1) limitations on the grasping force and torque, 2) detumbling operation along an arbitrary arm motion, and 3) parameter uncertainty in the target satellite, by parameterizing the manipulator hand motion. The consept of detumbling speed, determines the optimal control input and is also advantageous when handling dynamics parameter uncertainty in the target satellite.

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 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.

This paper discusses the target motion around the contact in the satellite capture operation using a free-flying space robot. The contact force has the potential for pushing the target beyond the manipulator reach or making the target have a tumbling motion. An impedance control is useful to prevent the robot hand from pushing the target. However, the relationship between the dynamics parameters, contact characteristics, and target motion have not been clarified yet. In this paper, virtual mass of impedance system (VMI) model is proposed to represent the influence of the hand impedance on the target motion. Using this model, the condition to prevent the robot pushing the target away is clarified.

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.

The interest on the study of asteroids has increased due to the recent missions that have been sent to explore such low gravity bodies. Due to its complexity, little attention has been given to close surface analysis by a mobile robotic system. In this paper, the authors present a study on the locomotion of limbed robotic systems based on the detection of friction force in an emulated microgravity environment. The issues rose by the microgravity environment and its effect on the dynamics of such robotic system during motion are addressed, and an algorithm to generate compliant motion gaits is presented. Experimental results show that the control system is capable of maintaining balanced contacts during motions.

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.

This paper addresses a time-optimal manipulator control strategy of a free-floating space robot with constraint on reaction torque induced by the manipulator motion. When a manipulator of a space robot is controlled, rotational motion of the base body is induced by the reaction torque. Assuming that reaction wheels are used to cancel the reaction and to stabilize the base attitude, the torque limitation of the wheels should be considered in order to realize zero base rotation of the robot. In this paper, a time-optimal control strategy of a free-floating space robot is discussed considering an arbitrary prescribed path for the manipulator hand and the dynamic constraints on reaction torque. The strategy is verified by numerical simulation with a free-floating space robot model equipped with a 7DOF (degrees-of-freedom) manipulator and a system of three reaction wheels.

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.

This paper discusses a control strategy of a free- floating space robot for capturing a non-cooperative target. It is desirable that the base attitude deviation of the robot is minimized for accurate operation by a manipulator arm mounted on it, for communication with the earth, and the ideal contact with the target so that the target would not be pushed away, impedance control and Distributed Momentum Control are reasonable for the above two requirements. The proposed strategy includes both control methods simultaneously using the manipulator's redundancy. Moreover, a control law for reaction wheels is proposed so that the singularity problem would not happened. The proposed strategy is verified from results of numerical simulations that compare the different degree of freedom manipulator.

This paper presents the design and gait analysis of a mobile rover for asteroid exploration. The basic requirement for the robot is to achieve scientific investigation of the asteroid surface at arbitrary locations with fine positioning capability after a large stride movement. This paper implements a general method for analyzing gaits, independent of the robot discussed, and could be applied to the gait of any legged robot; although special attention is given to creating a suitable gait for a nearly weightless environment. The discussion and simulation of different types of gaits in microgravity are addressed considering the principle of the motion using 3D computer simulation and control focused on the generation of statically stable and adaptable gaits so the rover advances with a desired speed and direction

This article introduces a new technique for planning reactionless paths to a point in Cartesian space, for manipulators mounted on a free-floating satellite. It is based on decomposition of the manipulator joint space into sets referred to as primitives which have redundancy one with respect to the attitude motion of the base body. The time duration of the manipulator motion is divided into sub-intervals. During a given sub-interval only one primitive is used. The choice of feasible sequence of primitives and times for their actuation, that satisfies given path constraints is made using mixed-variables optimization solver based on a mesh adaptive direct search algorithm

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

One of the most important phases of a satellite capturing operation by a space robot is the contact phase. During the contact between the end-effector and grasping point, there is a risk that the target and the robot can be pushed away from each other by the contact force. An impedance control of the hand with respect to the inertial coordinate is effective in keeping the contact with the target. In this paper, we propose a method for impedance control for a space manipulator. The end tip of the manipulator is controlled like a mass-damper-spring system fixed at a point in space in spite of the reactive motion of the base. In order to verify the proposed method, numerical dynamics simulations are carried out. Furthermore, an application of the proposed control to orbital service mission is discussed

On a scene of a natural disaster, rescuers require heavy duty hydraulic machines to answer their need of large forces, or to approach an unreachable spot. Those industrial vehicles are hydraulically actuated arms kinematically different, and equipped by specific tools to fit the task to accomplish. They require trained operators because of their complex use. As time and accuracy are primordial factors to save lives in such a situation, the use of automation and robotic concepts on the control of those machines becomes necessary. The standard approach is to use manual teleoperation based on a bilateral master/slave system, to enhance the maneuverability of the machines, but their diversity is nearly never taken into account. We propose here, a modular platform based on an original synchronization of module states that allows easy manipulator changes and flexibility of use. We will describe the proposed concept of intelligent interface, and verify its utility and performances through some pertinent configurations and experiment

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.

This paper deals with problems related to the capture of a tumbling satellite by a space robot. The minimization of the base attitude deviation before and after the contact with the target is discussed from the viewpoint of angular momentum distribution. By using the bias momentum approach during the approaching phase, impedance control during the impact, and distributed momentum control during the post-impact phase, we propose a possible control sequence for the successful completion of a capturing operation

This paper addresses an adaptive control of a space manipulator termed JEMRMS for vibration suppression. Space manipulators such as JEMRMS are subject to vibrations due to structural flexibility. To cope with such a drawback, control strategies for minimization of vibration excitation and for maximization of vibration damping have already been developed. However those strategies require an accurate model of the manipulator dynamics. If a payload with unknown dynamic properties is being handled, the use of the above stated strategies lead to vibration excitation, or to inaccurate positioning of the end point. In this paper, an adaptive control for the vibration suppression control is addressed to guarantee the stability of the system in the presence of model uncertainty.

In this paper, steering characteristics of an exploration rover on loose soil is studied. Analysis of the steering characteristics is a key to plan and control the motion trajectory of a rover. Traditionally, such analysis has been made based on a model called "bicycle model." In that model, a four-wheel car-like vehicle is approximated by a two-wheel bicycle-like vehicle with the fore-wheels and the rear-wheels paired. However, the bicycle model does not show a good performance when a vehicle travels off-road. In order to analyze the steering characteristics of a vehicle on loose soil, the authors develop a model that respects the dynamics of each wheel's slip and skid behavior. The developed model is called all-wheel dynamics model. In the all-wheel dynamics model, the behavior of each wheel on loose soil is modeled based on terramechanics. The motion trajectory of the vehicle is obtained by numerical simulation using the wheel-and-vehicle dynamics model. The validity of the proposed model is examined by the experiments of a wheel and a vehicle using simulated lunar-surface soil. The experimental results show that the proposed model provides a better approximation than the traditional bicycle model.

Space arms such as SSRMS and JEMRMS are designed by the concept of the macro-micro manipulator system, where the macro arm provides a long-reach capability and the micro arm performs the dexterous manipulation. One drawback however is that the macro part is subject to vibrations due to flexibility. Since the macro and micro parts are dynamically coupled, the motion of the small arm induces vibrations into the macro part hence, resulting in degradation of its positioning accuracy. To cope with this drawback, control strategies for minimization of vibration excitation and for maximization of vibration dumping have already been developed. However those strategies require an accurate model of the manipulator dynamics. If a payload with unknown parameters is being handled, the usage of the above stated strategies lead to vibration excitation, or to inaccurate positioning of the end point This paper presents two methods for on-line parameter identification of an unknown payload handled by JEMRMS. Both methods can be applied simultaneously while vibration suppression control is performed. The first one is vibrational motion based method, and the second one requires information about reaction forces and torques induced from the motion of the small arm. Simulation results illustrate the validity and applicability of both methods.

This paper deals with problems related to the capture of a tumbling satellite by a space robot. The minimization of the base attitude deviation after the contact with the target is discussed from the viewpoint of angular momentum distribution. A new capturing strategy utilizing bias momentum is introduced. By using the null space of the coupling inertia matrix we present a method for angular momentum redistribution while following a desired trajectory.

This paper presents a new strategy for capturing a free floating satellite initially having angular momentum. The main focus is on the base attitude before, during and after the catch. We use a joint space orthogonal decomposition procedure involving the so-called reaction null space during the pre-impact and post-impact phases. The idea of preloading bias momentum in a space robot system is discussed. Furthermore, we show that if proper post impact control is utilized the base deviation can be minimized.

In this paper, steering characteristics of a rigid wheel (tire) on loose soil is investigated. Based on terra-mechanic analysis, the lateral force characteristics of a driving wheel is modeled as a function of slip ratio and slip angle. The model suggests that the lateral force decreases according to the increment of the slip ratio and increases according to the increment of the slip angle. Such characteristics are confirmed and evaluated by experiments using simulated lunar-surface soil, called lunar regolith simulant. The proposed model is validated with the experimental results in reasonable precision. A model that properly predicts the lateral force can be useful for future practical issues, such as controlling the steering motion of a vehicle for following a desired trajectory in the operational phase, and also to compare the feasibility and/or stability of candidate steering maneuvers in the motion planning phase.

In this paper, the contact motion between rigid body systems floating in space is formulated and dynamic conditions are investigated in order to capture a non-cooperative satellite. As for the theoretical investigation, impedance matching is discussed for the case in which the robot hand under impedance control approaches and collides with a passive target, and a specific impedance value is defined to yield the matching. The impedance matching is understood to give a criteria if the contact is maintained with a target, or the target is pushed away. Experiments are carried out using two robot manipulators as a motion simulator of the chaser and target. Through the experiments, the concept of the impedance matching is verified, and a satellite capture operation is demonstrated using the strategy that an impedance controlled probe is inserted into the thruster nozzle cone of the target.

This paper investigates kinetic behavior of a planetary rover with attention to tire-soil traction mechanics and articulated body dynamics, and thereby study the control when the rover travels over natural rough terrain. Experiments are carried out with a rover test bed to observe the physical phenomena of soils and to model the traction mechanics, using the tire slip ratio as a state variable. The relationship of load-traction factor versus the slip ratio is modeled theoretically then verified by experiments, as well as specific parameters to characterize the soil are identified. A dynamic simulation model is developed considering the characteristics of wheel actuators, the mechanics of tire-soil traction, and the articulated body dynamics of a suspension mechanism. Simulations are carried out to be compared with the corresponding experimental data and verified to represent the physical behavior of a rover.

Presents the experimental results and post-flight analysis of reaction null-space based reactionless manipulation, or zero reaction maneuver (ZRM). The concept has been developed with an insight into the motion dynamics of free-flying multibody systems and its practical availability is clearly demonstrated with ETS-VII, a Japanese space robot. The ZRM is proven particularly useful for removing the velocity limit of manipulation due to the reaction constraint and the time loss due to waiting for the attitude recovery. The existence of the ZRM is very limited for a 6 DOF manipulator arm mounted on a free-flying base, but it is discussed how more operational freedom is obtained with a kinematically redundant arm.

We develop a collection of useful subroutines named SpaceDyn, in order to offer an open and free environment of numerical simulations to researchers both in robotics and space engineering fields. The SpaceDyn is a MATLAB toolbox for the kinematic and dynamic analysis and simulation of articulated multi-body systems with a moving base. Examples of such systems include a satellite with mechanical appendages, a free-flying space robot, a robotic system with structural flexibility, and a mobile robot, all of which make motions in the environment with or without gravity.

This article presents impact dynamic analysis of a free-floating space robot, subject to a force impulse at the hand. We study the joint and the base reactions in terms of finite velocity changes and clarify their role for the post-impact motion behavior of the robot. The analysis makes use of a joint-space orthogonal decomposition procedure involving the so called reaction null space. The article focuses on the specific case of a nonredundant arm and a reaction null space in terms of base angular motion. We further show that with proper post-impact control it is possible to transfer the whole angular momentum from the base toward the manipulator, and in the same time to reduce the joint velocity.

A composite control law for end-effector path tracking with a flexible structure mounted manipulator system is proposed, such that no disturbances on the flexible base are induced. The control law is based on the reaction null-space concept introduced earlier to tackle dynamic interaction problems of free-floating robots, or moving base robots in general. The control law is called composite since it ensures base vibration suppression control as well, although independently of the reactionless motion control subtask. The requirement of task independence is essential to avoid the appearance of complex dynamics expressions in the control law, such as nonlinear velocity-dependent coupling terms and dependencies of inertias on the elastic coordinates. We present experimental data from computer simulations and the experimental test bed TREP developed at Tohoku university. The experimental data is shown to agree well with theory.

This work is an extension of the authors' previous result (1995), mainly to tackle the post-impact control problem. We focus on the specific case of a nonredundant arm and a reaction null space in terms of base angular motion. It is shown that with proper post-impact manipulator control it is possible to swiftly transfer the whole angular momentum from the base toward the manipulator, and in the same time to reduce the joint velocity.

This work reports progress on a long-reach manipulator project. The original single-arm manipulator was complemented with an identical second arm. We introduce several noncontact motion control strategies which are based on the reaction null space concept. Experimental verification of disturbance compensation control via a single arm, and via the two arms while holding an object, is done. Also, motion feasibility on reactionless paths for a closed kinematic chain, including the two arms and the object, is examined.

A general framework for under-actuated manipulator systems is introduced. Within this framework, we show how to decompose the second-order dynamic motion constraint into two orthogonal components. Based on this decomposition, feedback control laws are proposed for motion stabilization to a reactionless-motion equilibrium manifold. Reactionless motion without drift is guaranteed for first-order nonholonomic systems. It is also shown that for a second-order nonholonomic system, reactionless motion in general leads to a drift.

The control of a dextrous manipulator mounted on a flexible structure is discussed. Using the concept of reaction null space, the manipulator dynamics is decoupled from the base dynamics. As a consequence of the decoupling, feedback control gains for structural vibration suppression and manipulator end-point control can be determined in a straightforward manner. We examine experimentally the performance of the above control tasks, using a planar experimental setup.

Under-actuated and macro-mini manipulators represent common characteristics in dynamics. This paper introduces a general formulation of kinematics and dynamics for manipulator systems which are composed of two types of generalized coordinate, active and passive, or primary and secondary. The generalized Jacobian matrix and the generalized inertia tensor, originally proposed for free-floating space manipulators, are redefined for general under-actuated manipulator systems. The reaction null-space and reactionless motion which are recently studied focusing to flexible-base manipulators, the compensability which is originally discussed for flexible-arm manipulators, and the measure of dynamic coupling, are proposed as examples of common properties for general under-actuated systems.

The problem of impact dynamics of Space robotic systems that consist of a rigid manipulator supported by a flexible deployable structure is addressed. Due to joint back-drivability and the dynamic coupling between the manipulator and its supporting structure, unknown motion of the system occurs after it makes impulsive contact with the environment. A method that uses the system's dynamic model is proposed to estimate the motion of the system after impact. This method which can be used to find ways to minimize the impact effect and vibrations of the supporting structure due to impact, is verified experimentally using the MIT Vehicle Emulation System (VES II). The experimental results show that the impact force and the system motion after impact can be reduced if the manipulator configuration prior to impact and the controller gains are properly selected.

Point-to-point operation of a flexible structure mounted manipulator systems (FSMS) is discussed. Four operation strategies: (1) straight-line path in joint space, (2) high-coupling path, (3) low-coupling path obtained from the coupling map concept, and (4) 3-phase motion obtained from the reactionless path are examined and compared in terms of a minimum oscillation of the supporting flexible structure, using an FSMS test bed, TREP, developed at Tohoku University.

This paper presents a practical control method for the robot satellite attitude to cope with manipulator reaction on free-floating space robots, developing the computed-momentum based reaction compensation (CMRC) concept. The author proposes versions of the CMRC control schemes based on angular momentum conservation in floating multi-link systems, practical schemes which require far less computation than the computed-torque based methods. The proposed schemes are demonstrated and examined by computer simulations using a realistic 3D model which involves the free-floating dynamics and the structural vibration of solar paddles.>

Investigates impact dynamics among free-floating multibody systems in space, by developing an extended inertial tensor concept, and establishes the theoretical basis for floating chain collisions. The authors have developed a concept named an 'extended inversed inertia tensor' (Ex-IIT), paying attention to free-floating behavior in the space environment. They apply Ex-IIT to impulse minimization arguments. To illustrate the magnitude of the impulses caused by link collisions in various conditions, the concepts of 'impulse index' and 'impulse ellipsoid' are introduced. By means of these concepts, the authors discuss the relationship of the impulse to collision directions and link postures, in order to determine the condition minimizing the impulse.

The authors present a basic formulation of motion dynamics of a free-floating rigid-link system to establish a basis of the collision dynamics. They propose a novel concept named extended generalized inertia tensor (Ex-GIT), which is an extended version of the GIT for ground-based arms, and discuss the virtual mass concept. By means of these concepts, they formulate the collision problem focusing on a velocity relationship just before and after the collision without sensing the impact force, but considering the momentum conservation law.>

An analysis of the momentum conservation equations of a redundant free-flying spacecraft/manipulator system acting in a zero-gravity environment is presented. In order to follow a predefined end-effector path, the inverse kinematics at velocity level is considered. The redundancy is solved alternatively in terms of pseudoinverses and null-space components of the manipulator inertia matrix, the manipulator Jacobian matrix, and the generalized Jacobian matrix. A general manipulation task is defined as end-effector continuous path tracking with simultaneous attitude control of the spacecraft. Three subtasks of the general task are considered. The case of manipulator motions that yield no spacecraft attitude disturbance is analyzed in more detail and a special 'fixed-attitude-restricted' (FAR) Jacobian is defined. Through singular-value decomposition of this Jacobian, corresponding FAR dexterity measures (FAR manipulability and FAR condition number) are derived.>

The control problem of multiple manipulators installed on a free-flying space robot is presented. Kinematics and dynamics are studied and the generalized Jacobian matrix is formulated for the motion control of a multiarm system. Individual and coordinated control of dual manipulators is discussed. For the coordinated operation, a new method of controlling two arms simultaneously-one arm traces a given path, while the other arm works both to keep the satellite attitude and to optimize the total operation torque of the system-is developed. By means of this control method, an interesting torque optimum behavior is observed and a practical target capture operation is exhibited by computer simulation.>

Presents a coordinated control of multiple manipulators in space free-floating robots. The authors firstly develop the generalized Jacobian matrix and equation of motion for a space robot with multiple arms, then propose a new control method optimising the sum of squared control torque in the sense of local (instantaneous) minimization by means of redundancy. The method is applied to realistic models installing a mission arm and reaction wheels, and also a redundant arm. Through the simulation study, this paper shows that the installation and utilization of the redundant arm has great effectiveness in terms of reducing the burden of reaction wheels for satellite attitude control.>

The authors establish a control method for space manipulators taking dynamical interaction between the manipulator arm and the base satellite into account. The kinematics of free-flying multibody systems is investigated by introducing the momentum conservation law into the formulation and a novel Jacobian matrix in generalized form for space robotic arms is derived. The authors develop a control method for space manipulators based on the resolved motion control concept. The proposed method is widely applicable in solving not only free-flying manipulation problems but also attitude-control problems. The validity of the method is demonstrated by computer simulations with a realistic model of a robot satellite.>