Assembly experiments are described that were conducted to evaluate direct calibration, a straightforward approach to the calibration problem for sensor-guided assembly systems. In direct calibration, the entire assembly system — the robot, the sensors, and the parts to be assembled — is calibrated for the required assembly task in a single procedure to directly determine the relationship between the part feature information in sensor coordinates and the part location in robot coordinates. This calibration procedure is accomplished in two steps: calibration data are generated by using the robot to move the part(s) to be assembled under the view of the sensors; and the best-fit mapping representing this assembly process is determined.
In this research project, the method of direct calibration is applied to the use of a vision-guided robotic system to install windshields in automobiles. Glass installation on the automotive assembly line is a delicate and difficult-to-automate assembly task. In the approach to windshield loading proposed herein, direct calibration is used to provide robust estimates of the location of both the windshield and the windshield opening, or aperture, in the car body. This location information is used to modify the taught insertion path such that each windshield is inserted into the corresponding aperture in the same manner that the windshield at calibration was inserted into the aperture at calibration.
To evaluate direct calibration as an approach in windshield loading and to determine the level of performance achievable with common industrial hardware, simplified 3-DOF assembly experiments were conducted. Results from these preliminary experiments indicate that direct calibration is a promising technical approach for the industrial application of automated windshield installation.