A Hybrid Visual Servo System Considering the Workspace Boundary Singularity

Robotic systems like humanoid frequently move to undesirable pose while being visually controlled at the boundary of its workspace, because the working environment is quite huge as compared with the robot´s workspace. The main objective of this paper is to deal with problems occurring at the boundary of the robot´s workspace. In addition, current typical problems on IBVS and PBVS, e.g., control in 2D and 3D space, task singularity, robustness to camera and robot calibration error, and robot singularity will be considered. To achieve the objective, the proposed two-stage visual servo system consists of exploring and positioning stages. In the exploring stage, given camera parameters, the target pose of the camera is estimated from the obtained images without the knowledge of the object. In the next positioning stage, a new hybrid control law that moves the camera equipped to a robot end-effector to around the target pose, which is estimated in the first stage and then positions it to the target pose more accurately using IBVS is proposed. Although the target pose is located out of the robot´s workspace, the proposed visual servo system shows the proper behavior at the boundary of its workspace. Finally simulation and experimental results shows the feasibility of the proposed visual servo system