Search

Investigation of small planetary bodies is now attracted and some missions on asteroids and comets have been realized. Such bodies are full of geographical features that next demand would be direct surface investigation by a rover. In order to navigate the rover to the specific points, the localization of the rover is required. However, conventional localization method is not adequate on small bodies whose size is less than 1[km]. One of the conventional methods, localization by camera images obtained on the rover needs a map made by a mother spacecraft. The resolution of the map is not enough for the rover's local view. Another method, localization by observing the movements of stars and the sun has little accuracy. Global positioning system (GPS) is not practical for small planetary bodies because it needs several orbiters. In this paper, we propose a reasonable method which localizes the rover on a small body with reasonable accuracy, with reasonable time and with reasonable resource. This method measures two way range between a rover and a mother spacecraft repeatedly. Even this method uses only one orbiter, the localization accuracy is estimated about 1[m] assuming ITOKAWA-size asteroidwhoseradiusisatmost600[m].

This paper proposes a new mobility system for planetary exploration robot using springs and linear actuators. In microgravity environment, it is difficult to obtain the horizontal velocity, because the friction force between a robot and the ground is very small. By pushing the ground, however, the robot can not only hop, but also obtain the horizontal velocity. The proposed hopping robot consists of two masses, and can push the ground by using springs. The robot can hop from the stationary state by transforming the elastic energy to the kinetic energy using the sprigs and linear actuators. Furthermore the robot can land without bounding by transforming the kinetic energy to the elastic energy. The simulation studies and the ground experiments show the effectiveness of the proposed mobility system.

In recent years, missions for exploring small bodies such as asteroids, comets, and meteorites have received a significant attention all over the world. The rovers which hang around the surface of such small planetary bodies can provide in-situ surface observations on the various points of the target body. So the research and development of exploration rovers for small planetary bodies are very important.Under the micro gravity environment such as on the surface of small planetary bodies, traditional wheeled rovers are not expected to move effectively due to the low friction and the inevitable detachment from the surface. This paper discusses the friction-based mobility around the surface of small bodies and proposes a new mobility mechanism that drives the rover by hopping. The hop angle and the velocity are analyzed by numerical simulations, which show the effectiveness of the new mobility system.

This paper deals with a free-flying space robot which grapples a target satellite based on a visual feedback control scheme. As the robot body is not fixed in an inertial space, manipulator motion causes changes in the view of the visual sensor. Therefore the closed loop system for the manipulator controller involves the visual data processing which normally takes long calculation time. We construct a control system which is not explicitly affected by the calculation time and analyze stability of the system. Analysis results show that a stable control system can be constructed in spite of the long calculation time, on condition that the manipulator trajectory which is not close to singular points is settled. Moreover we developed a zero gravity motion simulator which combined a computer simulation and servo mechanisms. An experimental space robot system is constructed and experiments to grapple a target are performed on the simulator. It is confirmed through the experiments that the free-flying space robot automatically grapples the target with the visual feedback control scheme proposed.

This paper describes a retraction control scheme for a space manipulator after grasping a floating object in space. Many control methods for a pre-retracting phase have been proposed by other authors. However those for a retracting phase have been very few, and the essential problem which an object is moving had not been treated so far. Firstly we divide a retracting process into four phases, and clearly show the problems to be resolved. Secondly we derive a new kinematic equation which relates angular velocities of joints with the integral of force and moment at an end-effector in space. Thirdly a force control method is proposed by using that important equation, and the possibility to grasp within the admissible error is proved effective: This control method corresponds to a velocity control for an end-effector feedbacking the integral of force and moment considering the derived kinematic equation. Fourthly we apply that control method to a retraction control, and demonstrate the stability of the proposed control scheme. Finally the effectiveness of the proposed retraction control method is shown by computer simulations.

This paper proposes a method for controlling a space manipulator with an end-effector for grasping a satellite floating in space. The previously published methods have two problems, (1) they have not dealt with the case where a satellite-manipulator-target system has translational and rotational momenta, and (2) they need much calculation when an end-effector linearly approaches a target's grasping point. We applied a sliding mode control method, and the first problem was resolved by considering momenta as external distubrances and the second problem was dealt by considering the exponential convergence of errors. And we proved a practical stability of the control which means that relative errors can be suppressed within a planned sphere in a finite time (for a case where angular velocities of the manipulator arms were controlled) . This control scheme uses observed data obtained on-board the spacecraft. Finally the practicality of the proposed method is investigated and the efliiectiveness of that is demonstrated by computer simulations.

This paper proposes two items: One is a sliding mode based on a new concept concerned with redundancy. The other is a control scheme based on that concept for a redundant manipulator in space to grasp a floating object. The previously published methods required many calculations becasuse of using pseudo inverse. To deal with this problem, we introduce a new concept of redundancy based on redundancy of sliding mode itself, and introduce a new sliding mode. This concept is combined with a conventional sliding mode control method. By using this hybrid control scheme the number of calculations is reduced to about 1/5 or 1/6 for tracking the same trajectory of an end-effector utilizing the redundancy as that of the conventional methods. And the proposed control method eliminates the necessity of the estimation of uncertain motion parameters of translational and rotational momenta by adaptive gains. Finally the effectiveness of the proposed method is verified by computer simulations for the trajectry control where the satellite angular velocity is surpressed by taking advantage of redundancy based on a new concept.

As space robots are used in zero gravity environment, there are some technical problems; the control scheme of the manipulator considering the reaction movement caused by the manipulator motion, the recognition scheme of 6 D. O. F. motion of the target, and so on. To solve these problems, we have constructed the ground simulation system combining numerical simulation and servo mechanisms. On this system, dynamics of the space robot and the target is solved based on the momentum conservation law, and the relative motion between them is realized. Using this simulation system, we can develop space robots efficiently. In this paper, we describe about the configulation of this system, simulation algorithm, results of evaluation tests.