Multi-camera visual servoing of a micro helicopter under occlusions

This paper proposes a switched visual feedback control method for a micro helicopter under occlusions. Two stationary cameras are placed on the ground. They track four black balls attached to rods connected to the bottom of the helicopter. The control input is computed by using the errors between the positions of the tracked objects and pre-specified reference values for them. The multi-camera configuration is redundant for helicopter control, but it enables us to design a switched controller which is robust against occlusions. An occlusion occurs when an object moves across in front of a camera or when the background color happens to be similar to the color of a tracked object. Multi-camera systems are suitable for designing a robust controller under occlusions, since even when a tracked object is not visible in a camera view, other cameras may track it. The authors have proposed a camera selection approach: If an occlusion is detected in a camera view then the other camera is used to control the helicopter. This paper presents another switched visual feedback control method for a micro helicopter under occlusions. This is called the image feature selection approach. This paper assumes that at most one tracked object is occluded at each time to simplify notations, although we can draw general conclusions. The errors between the positions of the tracked objects and pre-specified references are used to compute the control input, when all the tracked objects are visible. If one of the tracked objects is invisible, then the controller uses the errors given by the other three tracked objects. The position of the occluded object is also estimated by using the other three tracked objects.