Model Predictive Control Approach for assembling Large Components in Motion

The assembly of large components is characterized by a large number of varieties and a high process influence by environmental factors. For this reason the assembly in the field of truck manufacturing is in most cases carried out as a moving line with a high percentage of manual processes. Automation of these assembly process, albeit desired from a quality viewpoint, is presently limited as it requires the workpiece to be stationary. The ability to keep the workpiece on the moving assembly line while keeping the used handling systems flexible can enable business benefits. By assembling for example the windshield of a truck in motion, lead times can be shortened and floor space requirements can be reduced while at the same time the quality can be increased. To enable assembly in motion of large components, it must be possible to synchronize the movement between the handling system and the moving workpiece placed on an unguided transport system. Within this article we describe a Model Predictive Control Approach for robotic assembly of large components on moving assembly lines. One approach to synchronize the motion between product and robot is a direct metrological reference between them. This can be done by using an iGPS metrology system in which every handling system can be referenced to every work piece throughout the whole production line. The measurement system must be able to detect sufficiently small movements to ensure a reliable synchronization and thereby a high quality of the assembly process. The interaction of several systems makes for a number of restrictions. Here especially the delay times of the measuring system and the preset position for the robot have to be taken into consideration. To control the assembly process, a model predictive control loop is necessary. Only this control approach can meet the restrictions which are strictly necessary for the assembly. This article shows the first results and describes a demonstrator which has been set up to mount a windshield on a moving truck cabin with the help of a robot.