Define, integrate, implement MES with controls, ERP
Modern manufacturing execution systems (MES) can deliver the flexibility to enable manufacturers to define the solutions that meet their strategic needs. MES is what you make it: Define the MES functions needed, use standards, consider modularity, and integrate controls with MES and MES with enterprise resource planning (ERP), as needed.
Strategic enterprise integration has been in the making for the past two decades. While much of the technology to accomplish this integration is available, the number of companies actually claiming to have achieved any grand integration is few. The first generation of manufacturing execution system (MES) implementations were among the first technological categories tasked with providing the glue that would integrate all parts of the enterprise and established the potential of this category. However, their success was limited, partially by narrow and often conflicting definitions of what MES scope and functionality actually are. Today, a new generation of more open, flexible systems allows manufacturers to define MES in the way that works best for their operations.
An MES is a dynamic information system that drives effective execution of manufacturing operations. Using current and accurate data, the MES guides, triggers, and reports on plant activities as events occur. Ideally, an MES is composed of a set of functions that manage production operations from the point of order release to manufacturing through the point of product delivery, depicting all stages of the overall production process.
One of the most significant programs to define MES technology and its role in improving manufacturing excellence was the ISA-95 standard developed by the International Society of Automation (ISA), in league with the manufacturing community and system suppliers, including control, enterprise resource planning (ERP), and MES providers. (See sidebar at the end of the story: ISA-95 Enterprise-Control System Integration, Parts 1 to 6.) ISA-95 addresses MES concepts using the somewhat broader term of Manufacturing Operations Management (MOM), but both attempt to model the exchange of information between business logistics software and manufacturing operations software. They also model which activities the software can play and the exchange of information within manufacturing operations systems.
Figure 1 shows the ISA-95 functional hierarchy of levels of manufacturing decision making. At level 4, there are business planning and logistics decisions, which are supported by ERP and supply chain management (SCM) systems. Level 3 has been where traditional MES lives, providing tracking and trending information to support decisions in areas such as workflow, recipe control, and maintenance. At levels 0, 1, and 2 are decisions related to real-time production events, such as process sensing, manipulation of supervisory control, and process automation technology. This is the domain of distributed control, supervisory control and data acquisition (SCADA), and programmable logic controller (PLC) systems.
In addition to mapping out the hierarchies of manufacturing operations, ISA-95 also aims to improve interoperability among them, particularly between the ERP and MES systems. Figure 2 is a compact systems view of the ISA-95 standard mapped to the Purdue Reference Model. The dashed line indicates a possible border between ERP and the control system. In the most typical flow, scheduled orders pass to the control layer, which then returns the production response and capability information. The standard describes material, personnel, equipment, and other information required for an effective scheduling model. But it is critical to note that the standard does not intend to dictate exactly which system to use in which situations. It provides only neutral guidelines and data exchange structures that companies are expected to adapt to their own situations.
The ISA-95 standard also provides guidelines for defining the functional scope of manufacturing operations management activity. This includes definition management, resource management, detailed scheduling, dispatching, execution management, data collection, tracking, and analysis as they apply to the production, maintenance, quality, and inventory areas. Traditionally, MES has been viewed as a translation layer between ERP (level 4) and the controls and automation layer (level 2). In this role, the purpose of the MES system is to register and control-in near real time-all production orders coming from the ERP level. It does so by interfacing with the control levels to collect and provide real-time production data and return all the necessary logistics and financial relevant data back to the ERP. But defining the function of the MES in only this way does not do justice to its tremendous potential for improving manufacturing productivity, quality, and flexibility. Its ability to process real-time data, enforce business rules, and integrate them with engineering, quality, and production workflows make it the ideal platform for continuous improvement.
Loosening the categories
Realizing the true potential of MES requires shifting focus from trying to define where anything fits in the categories, to looking at what is needed to maximize production value for the end user. Ever since the Manufacturing Enterprise Solutions Association (MESA) created the first model, MESA and the industry in general have acknowledged that the boundaries between the different systems which co-exist in a manufacturing company are fluid, not rigid. When looking at the barriers between the ERP and MES software, for example, there is a clear overlap among many functions, such as planning, order control, human resources (HR), and maintenance management, to name a few. And likewise, there are overlaps between what might constitute the activities at the MES level and at the supervisory control level (level 2).
A modern analytical framework can help us determine the feasibility, the effort and cost, the flexibility, and the maintainability of deploying systems at various levels of the enterprise. Framework created by CGI/Logica, for example, categorizes 15 questions that can help manufacturers determine their software needs (Click here for more information).
The following are examples of criteria that can be used in deployment:
- Resolution: What data resolution is required for tracking and tracing?
- Response: Does the operation require real time data, or can it be processed in batch mode?
- Configurability: Is the configuration possible through out-of-the-box product features, or does it require custom development?
- Changeability: Is the manufacturing process expected to be stable over a given period of time, or does it require frequent changes and adaption?
Answering such questions guides the determination of the right system to implement each of the MES functions. While the ISA-95 standard makes it clear that such level-3 functions fit into the overall MOM scope, it does not dictate that all shall be necessarily implemented by a given MES solution. In fact, for some segments and for some industrial contexts, some of these functions might even be better fulfilled by the ERP.
Learn more about the case for modular MES and information about the six parts of ISA-95 Enterprise-Control System Integration.