Global calibration of a robot/vision system

The success of industrial robotic applications involving off-line programming and sensory-based guidance will depend significantly upon the positioning accuracy of robots, the accuracy of sensing devices and the software coupling between the robot controller and the sensors. These accuracy and coupling issues are addressed by a methodology developed for the automatic global calibration of a robot/vision system. The methodology employs a stereo-pair of CCD array cameras, which are mounted to the end-effector of a six-axis revolute robot arm. With an automatic procedure,three-dimensional coordinate measurements are made, relative to the robot's base frame, of a single spherical point in space at numerous and widely varying joint-angle configurations. Based upon a modified Denavit-Hartenburg robot kinematic model, both geometric and nongeometric robotic errors are inferred simultaneously with the geometric errors of the vision system using an iterative least-squares algorithm. Preliminary results indicate an approximately threefold improvement in positioning accuracy of the robot arm.