Fast recognition of cooperative target used for position and orientation measurement of space station's robot arm

When space station's robot arm performs auxiliary docking or target arresting, position and orientation between the visual sensor fixed on robot arm and the cooperative target on object must be measured in real-time, and its prerequisite is fast recognition of cooperative target. A fast recognition algorithm of cooperative target is proposed. The algorithm consists of three steps. To begin with, Sobel operator and the improved non-maximum suppression algorithm are hired to extract single pixel edges in the picture of cooperative target. Moreover, every edge is split into two sections, and each section is fitted into a circle using least square circle fitting method. If two halves have similar fitting results, the edge belongs to a circle. Finally, we draw two square windows around each circle according to the circle's radius, one big and one small. The number of straight lines that are in the complement area of the two windows and are close to the circle center is counted, and the cooperative target is identified if the number of straight lines suites the predetermined condition. Experiments using hand-eye camera, six-DOF turntable and the cooperative target are executed to test our algorithm. Results demonstrate that the proposed algorithm can accurately identify the cooperative target within a distance of 1.5 m regardless of lighting condition. In conclusion, the cooperative target recognition method is fast and stable and has strong anti-interference capability. , 2015, AAAS Press of Chinese Society of Aeronautics and Astronautics. All right reserved.