Profinet is a powerful communications technology that can provide access to process data and information which is needed by MES systems. In this article, Dr Peter Wenzel of PI (Profibus & Profinet International), Karlsruhe, Germany, explains how it provides excellent support for MES and ERP systems.
Propriety technology is providing access to data stored on automation systems that is needed by manufacturing execution systems (MES). Ethernet-based Profinet offers an excellent mechanism for capturing process data as well as information that is relevant in the context of MES.
Profinet is the open, vendor-independent Industrial Ethernet standard for the manufacturing and process industries. It makes use of TCP/IP and IT standards to provide seamless communication from the corporate management level right down to field devices. It offers scalable real-time communications up to clocked motion control.
Furthermore, Profinet can be used in safety-related applications to protect workers, machinery and the environment. The Profinet security strategy prevents unauthorised access and sabotage, and the proxy feature provides seamless integration of any fieldbus system into Profinet.
Automation of individual production cells, machines or entire production lines can be implemented using the scalable communication features of Profinet. Scalability means that a single communications system is sufficient to handle the full range of production applications. The key benefits are minimal hardware and software costs, efficient engineering and reduced system maintenance requirements.
Ethernet is the key to establishing seamless communication between the automation level and the office, and it takes the pain out of functional integration between the two levels. For supporting the functional vertical integration, the decision has been taken to create a Profinet interface to the MES level, and part of the specification is already in place.
MES and ERP
Integration of automation systems into MES and Enterprise Resource Planning (ERP) is becoming an increasingly important feature of corporate IT strategies. It enables companies to maximise utilisation of their production capacity. As companies strive to improve flexibility, enhance delivery performance and raise quality levels, they have continued to push the integration of their IT and production systems. They have also identified the need to eliminate gaps between their ERP and production automation systems.
MES software was introduced to improve integration and provide additional functionality. These systems are positioned between ERP systems and production automation and control systems.
The Instrumentation, Systems and Automation Society (ISA) has defined interaction models and uniform terminology in standard ISA S95. This is the major specification for MES, and it has largely been incorporated into international standard ISO/IEC 62264. The specification divides MES into four categories:
- Production
- Quality
- Maintenance
- Inventory
These 'operations' are included in the maintenance category. They describe actions within the MES and interaction between the MES and ERP systems. It has been difficult in the past to transfer information from automation systems to the MES because there were no established standards. However, PI (Profibus & Profinet International) has published the Profinet and MES Maintenance Operations guideline to address this problem. It describes Profinet functionality that is not directly relevant at the automation level, but which is very important for MES maintenance systems.
Condition monitoring
The status of a production asset is an essential piece of information that can be used to assess system availability, and this makes it a key parameter in the production planning process. The MES Maintenance Operations activity model needs status information as an input for planning and execution of maintenance activities.
Status information can normally only be provided by system components that have communications capability. These components can also act as proxies for components that do not have this capability. The availability of a standardised communications mechanism is extremely important to avoid extensive engineering work.
Profinet uses an expanded 'traffic light' model to represent device states. The warning levels 'maintenance request' and 'maintenance demand' have been added to supplement the device fault status. An additional 30 status conditions per device can be defined, and this ensures that maintenance state data (standardised device status information from the control system level) is adequate to handle future requirements.
The two warning levels can be used to distinguish between conditions that require attention without delay and conditions that can be addressed during scheduled preventive maintenance. They support simple implementation of condition-based maintenance wherever wear, contamination, etc can impair equipment operation. Manufacturers can define 'monitored entities' that are associated with device channels and are used to track device status. A channel can have one or more 'monitored entities'. A message is sent to the I/O controller whenever the state of a 'monitored entity' changes using the diagnostic alarms that are defined in the Profinet specification. This ensures that no information is lost and guarantees maximum transparency. Reporting the state change as an event avoids an increase in the communications load, and the status data can be accessed in acyclic mode.
There is a common definition of the 'maintenance state' for Profinet I/O nodes and Component-Based Automation (CBA) components. The status information for CBA components is stored in the component interface for the monitored entities and as a summary status for all of the components using the same syntax and semantics. The component manufacturer supplies the information to the interface.
Electronic device identification
Other Profinet functionality that is important in the MES context includes the ability to electronically and uniquely identify the devices that are installed on the system. Profinet uses the functions that are defined in the Identification and Maintenance Functions (I&M) guideline.
The basic I&M functions include the electronic nameplate that the manufacturer stores in the device and that can be read by the user. The nameplate contains device-specific data relating to items such as spare part selection, procurement and inventory, and it can also be used to schedule device updates. Some of the information contained in the electronic nameplate is as follows:
- device manufacturer
- order number
- hardware revision
- firmware revision
- revision number
In addition to the electronic nameplate, other I&M data has been defined that users can store in the device when they are installing the system:
- system and location ID
- installation date and comments
I&M data in the device is stored in data records which can be read in acyclic mode.
Conclusion
Profinet is a powerful communications technology that can provide access to process data and information needed by MES systems. It provides excellent support for both MES and ERP systems. The Profinet and MES Maintenance Operations guideline lays the foundation for future convergence of MES and automation systems by defining an open integration path between MES and Profinet-based automation systems.
