Shown at the Control show in Stuttgart earlier this year, Zeiss developed correlation-free measuring to ensure that component dimensions are measured reliably in the production line, beginning with the very first part.
With this system, companies no longer need to measure their car body components on a highly precise coordinate measuring machine (CMM) at regular intervals, and then transfer the identified deviations between the in-line and CMM measurements to the in-line measuring systems as correction values. “Correlation-free measurements will provide an entirely new foundation for in-line measuring technology and boost manufacturing efficiency,” says Dr Kai-Udo Modrich, head of Carl Zeiss Automated Inspection.
At the moment, says Zeiss, automotive manufacturers throughout the world monitor production using in-line measuring systems to meet their own high quality standards. These systems detect geometric deviations from defined characteristics and provide 100% inspection in the production cycle. The speed and precision at which the geometric characteristics are inspected depend primarily on the optical sensors used. For example, the Zeiss AIMax 3D sensor uses fringe projection to generate a point cloud in just a fraction of a second. By obtaining thick point clouds, multiple characteristics can be measured immediately with just a single capture thanks to Zeiss AIMax cloud. Moreover, even very small characteristics can be measured precisely and on different surfaces.
As is typical with all in-line systems, a flexible robot arm moves this sensor to the corresponding characteristics on the individual car body components. This method ensures that the entire measuring system provides accurate results, making subsequent measurements unnecessary. With traditional in-line measuring systems, reference measurements are performed on artefacts for reliable repeat accuracy. Active compensation is necessary for the robot arm extension, because of self-heating and changing ambient temperatures. As robot measurements typically have minimum absolute precision, the determined measurement values are usually offset by performing a comparison measurement on a CMM. The correlation is then checked using multiple measurements. The additional workload for the CMM in the measuring lab, as well as the time required pose a challenge in the automotive industry, but correlation-free measurements will make this a thing of the past.
But Zeiss’ correlation-free measurement approach ensures that component dimensions are measured reliably, beginning with the very first part. This system uses standard cameras to detect robots’ deviation from their specified position resulting from temperature influences.
These cameras are installed above the in-line cell and track every movement of the Zeiss AIMax cloud sensor without any difficulty.
There are markers on the robot arms and on the base of the in-line cell so that the system can determine the absolute spatial position of the sensors.
Thanks to this information and, most importantly, intelligent algorithms, the software developed by Zeiss detects deviations from the standard state and immediately filters these out.
Concludes Modrich: “Companies significantly expedite the ramp-up times for manufacturing new models and achieve the desired move rate more quickly. And that means real savings. Since the system already delivers reliable data beginning with the first part, it lays the foundation for implementing a closed production loop between the in-line measuring station and the welding robot, to take just one example.”
