Multisensor-based robotic manipulation in an uncalibrated manufacturing workcell

Abstract

This paper deals with the problem of locating a part moving on a rotating disc conveyor with the aid of a single CCD camera and conveyor encoders and subsequently manipulating the part with a robot manipulator. The precise position and orientation of the disc conveyor with respect to the robot manipulator is assumed to be a priori unknown. Likewise the position and orientation of the camera with respect to the robot is also assumed to be a priori unknown. In order to manipulate the rotating part, the robot controller relies on data obtained from multiple sensors. Among the various sensors that have been used in this paper, we have a single CCD camera which is held fixed in the workspace of the robot and which is able to detect features of the part as it rotates with the conveyor. Likewise, the camera is also able to detect features of the end-effector as it moves in the workspace. Additionally, the conveyor is assumed to be equipped with an encoder that measures the angular position of the rotating disc. What makes the robotic manipulation problem hard is that the precise position of the camera and the robot are a priori assumed to be unknown. Thus, the path that the end effector needs to follow is not a priori known in the coordinates of the robot but needs to be computed during the course of the manipulation. In this paper, a new multisensor fusion scheme is proposed that performs this computation. The advantage of the scheme is that it greatly weakens requirement on the image processing speed. Overall, our algorithm is able to handle lack of calibration between the robot, the camera and the conveyor, advantage of which is that it significantly shortens the setup time of the manufacturing workcell. The paper touches upon both the theory and the experiments. © 1998 The Franklin Institute. Published by Elsevier Science Ltd.