A Flexible Pose Measurement Technology For High-speed Targets Based On Monocular Vision

As the modern aerospace technology develops rapidly, there are higher requirements for the combat capability and cruising ability for a warcraft. The carrying capacity and separation performance of stores become significant guarantees of an aircraft's combat performance. During its flight, the aircraft has to drop stores in some circumstances. An improper separation of the store will directly affect combat performance of the aircraft and even threaten the safety of the mother plane. Therefore, it is necessary to measure the position and attitude parameters of the store after it separates from the mother plane, so as to ensure the safety of store separation during the flight. Wind tunnel testing is an important method to obtain store separation data during the middle stage of aircraft designs. In a wind tunnel testing, a store model is separated from the aircraft in the flow which is simulated according to the real environment in which the aircraft flies, then the position and attitude parameters of the separated model are measured by a set of non-contact equipment installed in the wind tunnel. Along with the increase in model types, there is heavier experimental task in modern wind tunnels. However, the existing position and attitude measurement methods in wind tunnels cannot meet the requirements for a wide range, high adaptability and high efficiency wind tunnel measurement. Therefore, the study of a flexible post measuring method to expand the scope of wind tunnel position measurement, and improve the flexibility of the measurement system as well as the efficiency of wind tunnel testing is of great importance. In this paper, we study the development of a flexible monocular pose measurement system based on the known theory of monocular vision measurement. The main contents in this paper are as follows:(1) Research on the pose measurement method for multi-dimensional movement targets based on the principle of monocular vision. In order to solve the problem that marker points may disappear from the field of view as the target rotates, a specific markers layout is designed based on the direction constraints of features on the target surface. Besides, an image processing method based on image subtraction and iterative in the time domain and space domain of image sequences respectively is proposed to accelerate the recognition and extraction of small image features in a large field of view. Results show that the six-dimensional pose parameters of a complex motion target can be measured with high accuracy using the proposed monocular position and attitude measurement method.(2) Research on a flexible post measuring method for wind tunnel models. In order to solve the problem that the measuring range is highly limited and vision sensors need to be re- calibrated during the measurement process, a post measurement method based on the parameterization of projection matrix define in monocular vision is proposed. And a transformation method between the two coordinate systems of camera motion is proposed to enhance the flexibility of the measurement system. Results show that proposed pose measurement method can obtain the position and attitude parameters of moving targets without re-calibrating the camera when the camera parameters such as the focal length, the direction and angular orientation are changed, improving the flexibility of the pose measurement system.(3) A flexible pose measurement system for wind tunnel testing is established according to the measurement requirements. According to the measuring requirements that camera parameters such as the focal length, the direction and angular orientation can be remotely controlled without camera re-calibration during the measurement process, a set of experimental equipment is selected, and the a control system for the equipment is designed. Results showed that flexible measurement requirements wind tunnel models can be satisfied using the established pose measurement system.(4) The pose measurement of moving targets is finished in the laboratory, and an experimental platform for the validation of the system accuracy is established. The position and attitude parameters as well as the measurement precision of the proposed system for different targets are analyzed. Results showed that the pose measurement system and method can achieve the post measurement of moving targets without camera calibration. The mean deviation of the displacement measurement in the X direction is 0.38 mm, while in the Y direction it is and 0.15 mm, the mean deviation of the pitch angle measurement is 0.36° and the mean deviation of the yaw angle measurement 0.33°.