A visual calibration method of monocular camera and pan-tilt for mobile robots

In the competition of 'RoboMaster', the robot, a mobile platform with a two-axis pan-tilt and a barrel, needs to shoot the target by launching a projectile. In order to detect and shoot the target automatically, we develop a visual system with a monocular camera mounted on the chassis. Based on some target detection algorithms, the target's 3D pose in the camera coordinate system is obtained. As the launching mechanism of the robot is on the two-axis pan-tilt, it demands to further obtain target's pose in the pan-tilt coordinate system to achieve precise shooting. Therefore, how to obtain the relative position between the camera coordinate system and the pan-tilt coordinate system is the main problem in our research. We propose a fast and effective method for the relative position calibration between the camera and two-axis pan-tilt based on specular reflection. We utilize a plane mirror to reflect the laser pointer light path mounted on the barrel. Then, the camera calibration method is applied to obtain the rotation matrix between the camera coordinate system and the world coordinate system. We finally verify the effectiveness of our method through experiments and achieve the first place in the competition.