Excerpted from a knowledge paper from Process Automation Systems, Siemens Energy & Automation Inc.
In the early 1990s, manufacturing execution systems (MES) were touted as the panacea for shop floor management problems, promising to do away with “islands of automation” and to seamlessly connect the plant floor with enterprise systems. Unfortunately, the early MESs were too vertical in scope. There was an MES for silicon wafer assembly, one for chemicals, another for packaging, and so on, with dozens of companies specializing in finely honed products for vertical applications. This contributed little toward ending the islands of automation, and the seamless connections often required skilled coding to connect to enterprise resource planning (ERP) and process control systems.
In some respects, the concept of MES was ahead of its time. Networking systems and operating systems weren’t quite ready to handle the degree of communication necessary between plant floor and enterprise systems. A potential solution to the communication problem—object-oriented communication—was developing both the PC-based operating systems (OS) often used on the plant floor and the UNIX systems typically used for enterprise systems, but definitions seemed to change with each new release of an OS. Distributed Component Object Model (DCOM) in Windows and Common Object Requester Broker Architecture (CORBA) in UNIX never quite seemed finished and were in a constant state of flux. In addition, the inability of these object platforms to communicate with one another impeded progress.
Bridge the Gap
Today, the availability of Web-based Extensible Markup Language (XML) communications successfully bridges the gaps between these systems, allowing object-based communications. Built on XML, the business-to-manufacturing markup language (B2MML) standard specifies accepted definitions and data formats for information exchange between systems and facilitates information flow and updates between systems.
An MES brings together many functions that fall outside the realm of the plant floor control system. Some of these include plant maintenance, laboratory information management, standard operating procedures, document control, training documentation, raw materials management, and corporate information flow. The MES pulls information from the ERP system concerning orders, bills of materials, work instructions, standard operating procedures, assets, assembly steps, and so on. It also creates a practical manufacturing plan based on prevailing factory floor conditions.
Recent changes make the MES an ideal partner with both plant floor systems and the corporate ERP system. When coupled effectively with an ERP system, today’s MES tightly integrates plant floor events with business events, empowers plant personnel with real-time/near-real-time vision into relevant events and metrics, provides accurate manufacturing costs based on productivity, and shows how much value was added on the plant floor on a shift, daily, or weekly basis. Because past MES/ERP integration problems often occurred due to a lack of definition as to the boundaries of each system, it’s important to define the role of MES functionality in a specific application before deciding how an ERP system might complement it.
Redefining the MES
While the MES has always promised to improve manufacturing agility—making it easier to introduce more new products, create smaller and specialized batches, and shorten lead times—it also satisfied requirements for electronic record keeping and traceability. But in today’s global markets, other important considerations include redefining MES implementation. These include global markets and production facilities, product quality and safety, production efficiency, and product genealogy.
Also helping to redefine the role of the MES is the four-level Instrumentation, Systems, and Automation Society’s (ISA) SP-95 Enterprise-Control System Integration specification, an international standard agreed upon by a consortium of manufacturers, system suppliers, and opinion leaders. This model breaks down business-to-plant floor operations into four levels.
Levels 1 and 2 include batch, continuous, and discrete control. (See Figure 1, p.35.) Level 3 (MES layer) includes manufacturing, operations management, dispatching production, detailed production scheduling, reliability assurance, and so on. Level 4 (ERP) defines business planning and logistics, plant production scheduling, operational management, and related areas.
An ISA SP-95-Compliant MES
With an ERP system at the enterprise level (top) and the control layers at the plant floor (bottom), an ISA-compliant MES will need to communicate data in both directions to help managers decide how to produce, what can be produced, when and what to produce, and when and what was produced. (See Figure 2, right.) In the ISA model, a B2MML layer provides connectivity between the ERP system and the MES. At the bottom, OLE (Object Linking and Embedding) for Process Control (OPC), which began as part of Microsoft’s COM/DCOM object model, connects data from the control system to the MES. The B2MML layer provides protocols for product definition, production capability, production schedule, and production performance. Product definition protocols bring data from the MES Product Definition Management module to the ERP.
Production capability protocols are used to pull data from the MES Production Resource Management module, and production performance protocols deliver data to the ERP from the MES Production Tracking System. Meanwhile, production schedule protocols send data from the ERP system to the Detailed Production Scheduling module in the MES.
The MES also consists of several other interconnected modules, including Production Dispatch, Production Definition Management, Production Execution, Production Data Collection, and Production Performance Analysis. Of these, the Production Definition Management, the Production Execution, and the Production Data Collection modules connect through OPC to the control system.
Improve the ISA Model
To make the ISA model provide real-time, dynamic, rule-based behavior to a real-world, flexible manufacturing system, some further steps help to make the system perform better and provide an easy-to-operate user interface.
First, a Data Integration Service (DIS) sublayer bridges the MES to the ERP system by encapsulating transactional data using B2MML. Second, to bring data from the OPC layer, a real-time, fully redundant data server feeds data to the MES and back to the control systems. It encapsulates data from the plant floor to make it easy for the MES to handle. In addition, the ISA Production Resource Management module can be expanded to include an equipment manager, a material manager, and a personnel manager.
The Production Dispatch module can be changed to a Production Order Manager, and the ISA Production Tracking module can be expanded to include a material manager, a production performance analysis, and a personnel manager. In addition, an historian has replaced the ISA Production Data Collection module, while the ISA Production Performance Analysis module’s duties have been expanded to include a Plant Performance Analyzer. While these modules cover information flow, two additional systems provide the flexibility for engineers to configure the system. A Report Manager provides data necessary for plant managers to run the plant, and a Client Application Builder allows engineers to design and build the MES.
Additional features that go beyond ISA SP-95 specifications provide more flexibility for MES system designers. For example, rules coordinate and synchronize machines, applications, and people. The system accommodates third-party software products and devices, as well as laboratory information systems and specification management systems, which assist users in managing and formulating product specifications for raw materials, semi-finished and finished products, and packaging materials. These systems can also distribute information across the company and throughout different departments.
Simplify Programming and Configuration
A framework approach to building an MES can eliminate trial-and-error spaghetti coding. For example, a graphical modeling environment, along with a strict separation between the production model and the operating components, provide better transparency and flexibility than a traditional approach to building an MES. Just as object-oriented programming reduces “reinventing the wheel,” an MES containing a hierarchy of reusable libraries can significantly reduce project costs and risks.
Also, the MES Client Application Builder with built-in Web server allows engineers to create and publish custom ASP.Net Web pages on a range of devices–from laptops to handheld computers. Data sources include the pro- duction modeler, MES components, the database, and the real-time data server.
Benefits of a Fully Integrated ERP/MES System
An ERP system provides business planning and logistics, plant production scheduling, operational management, and so on—all Level 4 activities. An MES (Level 3) provides manufacturing operations management, dispatching production, detailed production scheduling, reliability assurance, and so on.
In the past, some complained ERP systems tried too hard to provide what an MES does. Integrating an ERP system with an MES meant overlapping functionalities manufacturers couldn’t use or didn’t need. And, in many cases, an “MES functionality” provided within an ERP system was anything but comprehensive.
Today, it’s possible to integrate MES with ERP so that the systems are complementary and don’t overlap. Besides providing integrated workflow management at the business level of an enterprise, ERP systems can also provide supply chain and customer relationship management, as well as product lifecycle management. An MES manages workflow at the plant level of an enterprise, working with programmable logic controllers (PLCs), distributed control systems, and batch control systems. Manufacturers who have both systems can’t afford not to integrate them.
Businesses need to understand their combined manufacturing workflow before they start on the path toward MES/ERP integration. Business and production processes can be presented as a single workflow, with each step representing the functionality of a machine, application, or person. Each step is naturally more business or process oriented, and can, therefore, be plotted on a functionality allocation chart.
ERP functions can be represented on the top half and MES on the bottom half, with the two divided by a horizontal line. B2MML boxes on the chart represent communication/control channels between ERP and MES functions. Moving the borderline changes the balance of responsibility for functionality and workflow; lowering the centerline, for example, would reflect a more ERP-biased implementation. Manufacturers will need to go through this process to determine their own application needs.
Does It Work?
A leading food company in Spain prepares and packages top quality dairy products. Its 17 plants employ 4,000 people and create an annual turnover of nearly $1.2 billion. The company wanted to improve the genealogy, tracking, and traceability of its products—and to increase the efficiency of its filling lines. It also needed to provide for personnel management and production reports. The company also wanted a Web interface for the MES, as well as the ability to connect the MES to its ERP system.
The company installed the Siemens SIMATIC IT Production Suite, Historian, Report Manager, and Server, which provides a direct interface to the ERP. The results were positive, meeting the company’s requirements and, in many cases, going beyond its basic needs.
The integrated MES/ERP system provides a common solution for all plants, because each is based on a standardized product. The system provides full traceability of products and ingredients, improves production efficiency and flexibility, and manages key performance indicators.
Another Spanish manufacturer, one that makes electro-welded mesh and reinforcing joints—with an annual turnover of 90 million—has also seen the results of a combined and integrated MES and ERP system.
Summing up, the benefits of MES-to-ERP integration go far beyond the rudimentary integration efforts. To become agile and responsive, manufacturers must gain vision into their operations to make decisions based on real-time information, understanding the impact of those decisions and the alternatives that may be available. Joining manufacturing with planning systems is the first step towards that agility.