Calibration Method And Application Of Pan-tilt Motion Parameters With Integrated Camera And LRF

In recent years,optical camera and LRF(Laser Range Finder),as the two most common environmental sensing sensors,have been widely used in the fields of robotics,surveying and mapping,and autonomous driving.In the application of environment sensing scene,the field of view of a single sensor is often limited,and the cooperation with the motion actuator can expand the field of view of the sensor under the condition of maintaining the imaging accuracy,and achieve flexible and diversified imaging methods.As one of the most common motion actuators,the pan-tilt is often transformed into complex multi-angle imaging systems for cameras and LRF.The key factor of pan-tilt rotation imaging is the need to accurately calibrate the geometric relationship between the rotating pan-tilt and each sensor,as well as the geometric parameter relationships between different types of sensors.This paper takes the movement parameter calibration of a rotating pan/tilt equipped with a camera and an LRF sensor as the research objective.The research content is as follows:(1)Two types of pan-tilt terminal designs with different degrees of freedom.The design includes a single-axis pan-tilt equipped with 2D-LRF,and a two-axis pan-tilt equipped with a camera and 2D-LRF sensor.Deduced the geometric parameter models of the pan-tilt with different types of sensors,designed a set of indoor U-shaped calibration boards for calibration of various sensors and pan-tilt geometric parameters,and compiled the corresponding image and laser data acquisition software;(2)Research on internal parameter calibration of camera sensor.The disadvantages of Zhang Zhengyou's calibration method under the condition of limited rotational movement are studied,and the ChArUco calibration board is designed to automatically calibrate the camera's internal parameters of the small hole imaging;(3)Research on camera and LRF external parameter calibration.The role of U-type calibration plate in external reference calibration of different sensors is introduced.The point cloud data returned by 2D-LRF were preprocessed by homogenization upsampling,laser filtering and image spatial conversion.A robust point cloud key corner extraction algorithm was designed to determine the coordinates of the corner points in the world coordinate system,and then the external parameters of the camera were obtained through the checkerboard calibration method.The coordinates of the corner points with the same name in the image coordinate system were calculated,and the external parameters between the camera and the LRF sensor were optimized to minimize the backprojection error.(4)Research on the calibration method of the rotation axis parameters of the pan-tilt.Considering the various sensors mounted on the pan-tilt as a particles,the rotational movement of the pan-tilt can be abstracted as the problem of a point in space rotating around arbitrary axis.First,the mathematical model of a point in space rotating around arbitrary axis is derived;then different calibration strategies are adopted for the acquisition terminal of the two types of different configurations of the pan-tilt,and for the pan-tilt only integrated with LRF,the rotation parameter values are calculated by using the search strategy from coarse to fine based on the sequence point cloud;for the pan-tilt that integrated the camera and LRF at the same time,based on the rotation axis parameters obtained by using LRF,and then according to the key point coordinates in the image obtained by rotating the camera around the acquisition terminal and combining with the external parameters of the camera and LRF in the previous chapter,can achieve higher precision of the rotation axis parameter calibration;(5)Application of pan-tilt geometric parameters.The two types of pan-tilt terminal are used in two projects respectively.The single-axis pan-tilt with integrated LRF is used in the three-dimensional shape scanning of coal piles in large scenes and the digital twin system of stacker and reclaimer,and the multi-axis pan-tilt with integrated camera and LRF used in the bridge inspection robot system,the application of the calibration parameters in the above systems and the effect of taking the ground are explained separately.