Visual control of 6 DOF robots with constant object size in the image by means of zoom camera

Abstract

In this paper a new approach for robust visual-servoing in 6 degrees of freedom (DOF) is described. The procedures of image-based visual-servoing provide calibration robust methods for visual control of robots. One of the main problems for visual-servoing with a gripper mounted camera is the variable object size due to camera movements. This leads to very high demands on the object recognition algorithms. Furthermore, with the decrease of the object size in the image, the influence of measurement noise increases. In this paper, an approach using a zoom camera to get constant object sizes during movement is described. Object identification is simplified and the influence of measurement noise is reduced. Because of the variable focal length objects may become invisible by the camera due to gripper movements. Pose control in 6 DOF is used to overcome this problem. The control strategy is divided into the phases exploration, rough-approach, alignment, and fine-approach. Marked objects are introduced to the system by teaching-by-showing. The whole process is calibration robust and therefore suitable for only rough calibrated camera and robot systems. No object knowledge, except the distance of the object to the camera while teaching, is used for adaptation of the system model. The approach and its verification by a simulation is described in this paper.