Study On Vision-Based Operation For Satellite On-Orbit Self-Servicing

If the satellite is able to maintained on-orbit or be serviced by itself, not only the lifeof the satellite can be extent, and its performance can be enhanced in space systems, butalso the substantial costs of waste and the growing problem of space junk can be reduced.In recent years, the development of space robot technology shows that its great potentialin the satellites self-servicing. The work of this dissertation is supported by Commissionof Science Technology and Industry. All experiments are done on the satellite on-orbitself- maintaining system's experimental platform developed by robotics institute, HarbinInstitute of Technology. The major work focuses on pattern recognition, visual objecttracking, visual servoing, and map-based operation for space robot.Image feature extraction plays an important role in pattern recognition, amongwhich, Corner is a quite important feature. In our work, Harris corner detector is im-proved. On this basis, a corner-based feature selection method is proposed for the char-acteristics of the objects in satellite having obvious edge and corner as man-made ob-jects. New method reduce the required number of features. JointBoost has been widelyadopted to detect different kinds of objects. It's improved by combining multiple clas-sifiers in a cascade to get faster detection speed and higher classification accuracy. Thepose of the object should be calculated after the object is identified so as to enable robotto complete the operation on the target object. To achieve higher precision, an optimizedthree-dimension coordinate on-line measurement method based on collinear constraintin derived, in which Direct Linear Transformation (DLT) method is utilized to determinethe initial values for the iterative process.Automatic target tracking in image sequences plays also important role in com-puter vision. The methods based on hausdorff distance track objects by calculating thehausdorff distance between the objects in both ideal model and actual images. It's atime-consuming method because of that such distances are calculated for each pixels inthe image. To overcome such disadvantage, particle filter is implemented, the hausdorff-distance will be calculated for some sample pixels, in the sequel, the computational costis decreased. Through comparison with the advantage and disadvantage between thepatch-based tracking method and the active contour tracking method, a novel methodcombing the patch-based tracking method and the active contours tracking method isproposed, which is robust against occlusion and has better accuracy. In the aspect of visual servoing, the concept of the generalized distance in two posi-tions and orientations of robot is defined in the dissertation and a new method for motionplanning based on the generalized distance of position and attitude is proposed. Onlythe robotic direct kinematics is, and the robotic motion is divided into many stages. Thejoint displacements during each stage are determined with heuristic information providedby decreasing the generalized distance between the end-effector and the target and theoptimal joint displacements is determined by the meanshift algorithm. The new methodavoids robot singularity problem in the process of visual servoing, and and improves thesafety of robot operation.The impedance control based on joint torque is implementedinto the visual servoing algorithm. While executing contract task, the visual servoingcan provide the tactile information with high accuracy, in the sequel, the satellite self-Servicing platform's adaptability and compliance capability to environment can be im-proved.In order to solve current problem in the space robot operation, such as big timedelay, restriction about communication bandwidth, a novel operation based on map ispresented, in which visual algorithm mentioned above is involved. Firstly, the map iscreated after the operator finished the operation in virtual environment, and then therobot is navigated by the map to finish the actual task. Virtual environment modeling,interface design, map building, robot navigation involved in the operation based on mapare discussed in detail.At last, three experiments are carried out successfully with the platform of SOOSS,thus verify the efficiency of the proposed tele-operation method.