Application domain: SMART FACTORIES
Here is an extract from 'The IEC 61499 Function Block Standard: Launch and Takeoff', by Thomas Strasser et al.
Mass customization of footwear is characterized by very dynamic and heterogeneous demand for products whose features are customized to user requests, and by generally high production volumes, thus justifying the adoption of highly automated production systems. The high number of product variants and possible customizations, together with the need to match evolving production requirements and market trends, can be accomplished only by relying on extremely agile and reconfigurable production solutions. A production system has been developed to meet the challenging requirements of this market. The resulting modular and reconfigurable system architecture, illustrated in the figure, comprises a number of production islands 24 connected by a flexible transport system. This system was named the European Best Practice in mass customization in 2009. The production system architecture is composed of the following main production phases: (1) cutting of shoe components, (2) stitching of the shoe upper components, (3) last milling, (4) shoe assembly and roughing, (5) sole application, (6) shoe finishing, and (7) packaging. In order to match the evolving production requirements, the production system has been conceived with two major characteristics:
- Flexible transport system: Different shoe production cycles require the product to visit different production stations – within each phase – according to specific sequences of operations. This results in a high number of alternative routings across the shop floor depending on the production process to be executed. As a result, the transportation system has been designed as a scalable line composed of a number of standalone mechatronic modules. In turn, each module is composed of two transport and dispatching units, the table and the manipulator and a buffering island, serving specific machines disposed it. This mechanism enables each item to reach equally well any operation unit of the shopfloor coherently with the process plan.
- Flexible and reconfigurable machines: Machines have also been conceived with reconfigurable and flexible fixturing and tooling systems, to match frequent changes of product geometric and technological features. As example, within the robotized roughing cell, flexibility has been exploited with reference to (i) dedicated multifunctional tools for differentiated shoe roughing and gluing, (ii) a flexible gripper for fixturing and handling of items with extremely different shapes and dimensions, and (iii) variable geometry tool path generation.
Agility and reconfigurability requirements necessitate complex and flexible automation infrastructure, characterized by different hierarchical levels covering several control tasks - from the single control loop to the supervision, coordination, and scheduling activities.
With specific focus on the control system, a distributed and modular architecture has been designed coherently with the standard IEC 61499. The adoption of this standard has been driven by two major advantages. On the one hand, it supports the control software development across its lifecycle from the control specification, the architecture and functional design, the algorithm development until the implementation, verification and validation up to the final deployment of the control software into the real target. In addition, the development of a control software solution for a reconfigurable manufacturing system requires very high levels of software modularity, integrability, diagnosis, customization, and convertibility.
Compared to traditional control solutions characterized by monolithic, rigid and looselycoupled architectures, the development of IEC 61499 based control software is conceived to enable efficient control modifications without a major overhaul of the entire software so to accomplish the integration and/or substitution of portion of the control software driven by system reconfigurations or adaptations.
The shop floor control system solution relying on IEC 61499 standard has been implemented in ISaGRAF 5.2 workbench. Specific Function Blocks of the implemented control system incorporate a set of control 25 algorithms devoted to ruling single controlled mechatronic components, as well as module optimization policies whose goal is to compare the actual and nominal behaviors of components and executing an adaptation if necessary. Full modularity and reconfigurability of single modules is thus supported, both from hardware and from software point of view. In fact, twofold automation reconfigurability has been incorporated in the control Function Blocks, facing both forecasted and unforeseen events:
- Offline predictive reconfiguration: The control system comprises some latent Function Blocks, coupled with forecasted system physical reconfigurations so that as soon as the physical reconfiguration will occur, the correspondent control modules are activated by Function Block events.
- Online dynamic reconfiguration: When a new intelligent unit is introduced in the system, it openly shares its functional description, process capabilities, and requirements. The recognition phase involves the comprehension of the entity features to be exploited within the production environment so to enable the integration of the new entity (new Function Blocks,) within the control infrastructure.
Both the offline and the online control reconfiguration policies require - beside the control module integration at shopfloor - an adaptation of the dispatching process. For each single product, it ensures the understanding of the mapping of tasks to be performed vs. resources, dynamic step by step building of consequent product routing, and resulting distribution of tasks across (new) available resources. The deployment of such a solution evidences how the IEC 61499 approach extends not only “horizontally” (i.e., at shopfloor level), but also vertically , involving supervisory and control management levels.
An example of offline control reconfiguration is related to the roughing and cementing robotic cell. The robotic cell control has been implemented by considering a set of production cases, with each representing the sequence of operations to be performed for the specific part type. Together with the production cases related to the actual part types to be processed, there is a number of cases related to parts types which are not at the moment under production but are expected to be included in the future. As a result, when the new part type will be introduced in the product portfolio, the control will be robust in the reaction so that it will be automatically capable of recognizing the part type and associating it to one of the existing specific cases.
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