A study on real-time implementation of visual feedback control of robot manipulator

摘要

Presents an approach to real time implementation of visual feedback control for a robotic manipulator. There are mainly two ways to put the visual feedback into practice. One is called look-and-move and the other is visual servoing. The former is the method which transforms the position and orientation of an object obtained by a visual sensor into those in the world frame fixed to an environment and guides the arm of the manipulator to a desired location in the world frame. Visual servoing uses the Jacobian matrix which relates the displacement of an image feature to the displacement of a camera motion and performs a closed-loop control regarding the feature as a scale of the state. Therefore, we can construct a servo system based only on the image and can have a robust control against the calibration error because there is no need to calculate the corresponding location in the world frame. In order to control the position and orientation of a robot with respect to an object, a new technique is proposed using binocular stereo vision. The stereo vision enables us to calculate an exact image Jacobian not only around a desired location but also at other locations. The suggested technique can guide a robot manipulator to the desired location without giving such priori knowledge as the relative distance to the desired location or the model of an object even if the initial positioning error is large. The performance of the proposed visual servoing system is illustrated by the experimental results and compared with the case of conventional method for an assembling robot with four joints.