Yubo Guo

2-DOF Angle Measurement of Rocket Nozzle with Multivision

A real-time measurement method is presented for the 2-DOF swing angles of rocket nozzle by the use of multivision and rocket nozzle rotation axes. This method takes offline processing to measure the position of two nozzle rotation axes in image coordinate system by means of multi-vision and identify the rotation transformation relation between image coordinate system and fixed-nozzle coordinate system. During real-time measurement, the nozzle 2-DOF swing angles can be measured with transformation of marker coordinate from image coordinate system to fixed-nozzle coordinate system. This method can effectively resolve the problem of occlusion by markers in wide swing range of the nozzle. Experiments were conducted to validate its correctness and high measurement accuracy.

Pose measurement model of space cooperative target capture based on zoom vision system

In view of the mission of the cooperative target capture with the space manipulator, this article proposes to establish pose measurement model of the space cooperative target capture based on thick lens model for the first time. First, a ground simulation system is established for the cooperative target capture with the space manipulator based on the zoom vision system, coordinate system is defined, and pose calculation process is given. Then, space coordinate measurement model and pose calculation model are established for the system. Finally, the simulation experiments are conducted and the results validate the algorithm model and the high accuracy of measurement.

Real-time calibration of space zoom cameras based on fixed stars

Compared with fixed focus cameras, zoom cameras can be used to provide more precise measurements in space tasks. However, the calibration of zoom cameras in this case is a difficulty, as it is not convenient to set up a calibration device on the spacecraft. To solve this problem, the authors present a real-time zoom camera calibration algorithm based on fixed stars. With the star images captured by the zoom camera, they firstly use a star identification method to recognise the identity of stars. By means a series of coordinate transformation, they are able to build the one-to-one mapping between the pixel coordinates and epoch celestial coordinates of the stars. Finally, the internal and external parameters of the zoom camera are obtained based on the thick lens zoom camera model. Simulation and experiment results show that the internal parameters of zoom cameras are rarely affected by the noise of latitude, longitude and time. Furthermore, the calibration precision and robustness of focal length reaches a satisfactory level.

Effective ellipse detection method in limited-performance embedded system for aerospace application:

Up to present, there have been numerous articles on ellipse detection. However, it is still a great challenge especially for embedded application with restricted available computing and memory resources. To handle this problem, a novel and effective method is presented for ellipse detection. The method consists of two main steps: extraction of elliptic edge contours and edge contours grouping. These two steps are integrated to improve the accuracy and speed of the method. Finally, the aim of this method is to process high-resolution image for embedded system, which needs fast and accurate ellipse detection with limited computational and memory resources.

Space camera optical axis pointing precision measurement system

In order to realize the space camera which on satellite optical axis pointing precision measurement, a monocular vision measurement system based on object-image conjugate is established. In this system the algorithms such as object-image conjugate vision models and point by point calibration method are applied and have been verified. First, the space camera axis controller projects a laser beam to the standard screen for simulating the space camera’s optical axis. The laser beam form a target point and has been captured by monocular vision camera. Then the two-dimensional coordinates of the target points on the screen are calculated by a new vision measurement model which based on a looking-up and matching table, the table has been generated by object-image conjugate algorithm through point by point calibration. Finally, compare the calculation of coordinates offered by measurement system with the theory of coordinate offered by optical axis controller, the optical axis pointing precision can be evaluated. Experimental results indicate that the absolute precision of measurement system up to 0.15mm in 2m×2m FOV. This measurement system overcome the nonlinear distortion near the edge of the FOV and can meet the requirement of space camera’s optical axis high precision measurement and evaluation.