Field-Level Reconfiguration of Real-Time Distributed PLC Operating Procedures

Volatile market conditions like fluctuating supply and regulatory uncertainty require quick adaptions of production recipes (i.e. procedures) on the field-level. In process engineering, promising research targets so-called orchestration, and shop floors with series-produced machine tools effectively form Reconfigurable Manufacturing Systems. Both are highly adaptable to changing product orders, unlike many special-purpose production machines, whose flexibility requirements must be reconciled with the inherently static programming standard IEC 61131 for PLC control. The control software is large and closely intertwined by dependencies to fulfill extra-functional requirements. It traditionally does not expose individually callable functions as building blocks for changeable procedures, but recent advances towards skill-based software engineering are changing that. These approaches however need an external device to invoke skills one-by-one or in limited sequences. This work instead proposes IEC 61131-3 compliant data structures and execution algorithms for runtime-changeable procedures with sequential, conditional and alternative control flow that are executed entirely on one or more distributed PLCs in real-time. They are implemented successfully on a discrete manufacturing demonstrator showcasing procedure reconfiguration without control software changes and without involving additional devices in the control.