On the origin of deadlocks in robotic cycle shop control

For the large class of process plans which include transport loops and multi purpose machines, we analyze the deadlock behavior and provide control structures to cope with blocking of production lines. We present a modular approach to deadlock control based on Petri net representations. By synthesizing large systems from generic plant and control modules, a great range of practically important scheduling tasks can be solved which theoretically are NP-hard. The approach is applied to large industrial settings of 25 machines arranged in several loops and multi loops.