Enhancements to off line programming through improvements to robot kinematic performance.

Abstract

Off-line programming techniques have been developed to improve productivity of advanced robot systems. In the manufacturing industry, they enable robot workcells to be simulated and robot programs to be generated without interrupting the production process. However, due to the poor structural integrity of present-day robots, discrepancies exist between the CAD model used in the off-line programming system and the real robot. These discrepancies severely limit the effectiveness of off-line programming techniques, since manual operator intervention is required to modify the off-line generated trajectories required for the robot to operate in the manufacturing cell. The work presented here addresses the problems associated with some of these discrepancies to enhance off-line programming systems, by concentrating on two aspects of robot kinematic performance. Identification of the 'actual' kinematics of the manipulator using a new calibration methodology enables the static positioning accuracy of the device to be improved. Validation experiments have been performed using the new kinematic calibration methodology. Identification of the 'actual' kinematics of a Puma-560 industrial robot has shown that this robot's average positioning error can be reduced by approximately 93%. By providing the workcell designer with a new performance index known as the Condition Vector as an indication of the variation in robot kinematic performance throughout its workspace, workcells can be arranged and robot postures selected based on desired robot characteristics for prescribed tasks. Validation experiments for the Condition Vector, undertaken on two industrial robots, were not conclusive but provided promising results.