Unicycle-like Robots with Eye-in-Hand Monocular Cameras: From PBVS towards IBVS

This chapter presents an introduction to current research devoted to the visual servoing problem of guiding differentially driven robots, more specifically, unicycle-like vehicles, taking into consideration limited field of view (FOV) constraints. The goal is to carry out accurate servoing of the vehicle to a desired posture using only feedback from an on-board camera. First, a position based scheme is proposed, adopting a hybrid control law to cope with limited camera aperture. This scheme relies on a localization method based on extended Kalman filter (EKF) technique that takes into account the robot motion model and odometric data. To increase the potentiality of the visual servoing scheme with respect to existing solutions, which achieve similar goals locally (i.e., when the desired and actual camera views are sufficiently similar), the proposed method visually navigate the robot through an extended visual map before eventually reaching the desired goal. The map construction is part of the approach proposed here, which is then called visual simultaneous localization and mapping (VSLAM) for servoing. Position based scheme accuracy are intrinsically related to the effectiveness of the localization process, which is related to the estimation of 3D information on both the robot and the environment. A shortcut overcoming the estimation process uses visual information directly in the image domain. In this spirit, an image based scheme is presented. The controller is devoted to constantly track desired image feature trajectories. Such trajectories represent optimal (shortest) paths for the vehicle from the 3D initial position towards the desired one. Optimal trajectories satisfies the additional constraint of keeping a feature in sight of the camera and induces a taxonomy of the robot plane of motion into regions. It follows that the robot uses only visual data to determine the region to which it belongs and, hence, the associated optimal path. Similarly to the previous case, the visual scheme effectiveness is improved adopting appearance based image maps.