Research On Pose Estimation And Hovering Calibration Of Quadrotor Based On Optical Flow Sensor

In this paper,a quadrotort was used as the application platform.Aiming at the problem of inaccurate hovering calibration of the quadrotor,a pose estimation and hovering calibration method for the quadrotor based on optical flow sensor was proposed.The main work of this thesis includes three parts: the construction of the mathematical model for the quadrotor,research on improved algorithm of optical flow sensor,research on the algorithm of the pose estimation and the hovering calibration for the quadrotor.Finally,the flight test of the quadrotor was carried out.(1)Construction of mathematical model for the quadrotorBy analyzing the transformation relationship between the body coordinate system and the navigation coordinate system and the basic movement mode of the quadrotor,the basic principle of the motion control of the quadrotor was introduced.On this basis,the mathematical model of the quadrotor was constructed according to the Newton-Euler method.It is theoretically given that the parameters was needed by estimating the pose of the quadrotor and completing the hovering calibration of the quadrotor.(2)Research on Improved Algorithm of Optical Flow SensorThe inter-frame images are acquired and processed by the optical flow sensor.In order to overcome the problem that the time of calculating for the traditional optical flow algorithm was too long or the algorithm was sensitive to illumination,the continuous inter-frame optical flow field was calculated by VOD block matching criterion.In order to reduce multiplication calculation of VOD block matching criterion,The SEA algorithm of VOD block matching criterion was adopted.the sub-pixel refinement was obtained by using the bilinear interpolation algorithm,in order to obtained the optimal motion vector of the sub-pixel level.Then,the optical component of the image plane x and y was obtained by the rotation compensation algorithm.Finally,the horizontal movement speed of the camera relative to the ground was calculated by metric scaling.(3)Research on the algorithm of the pose estimation and the hovering calibration for the quadrotorThe SEA algorithm of VOD block matching criterion was used to calculate the inter-frame optical flow field,and the horizontal velocity of the quadrotor relative to the ground was obtained by bilinear interpolation,rotation compensation and metric scaling.Then,according to the relationship between the speed and attitude angle to compensate the attitude angle measured by MTI-G sensor and then get high-precision attitude angle.And then using the optical flow sensor to measure the height of the quadrotor from the ground.Finally,Using PID control on the attitude angle and height of the quadrotor,thus,quadrotor can export a certain duty cycle PWM wave and control the motor speed,and ultimately hovering in a small area.The quadrotor mastering platform based on Pixhawk was set up.And the platform integrate optical flow sensor module PX4 FLOW,and then use PX4 FLOW to collect continuous images.Then,in MATLAB,the SEA algorithm simulation experiment based on VOD block matching criterion was carried out on the image obtained by the camera,and the theoretical reliability of SEA algorithm of VOD block matching criterion was verified.And it is advantageous to estimate the pose of the quadrotor.Finally,the quadrotor can hover in a certain area.