Manufacturing Execution Systems
There has been significant innovation and market growth in the Manufacturing Execution System (MES) arena in the last decade. This article will provide a description of the evolution of MES to date, a description of what an MES is and does, and provide insight into how an MES can be modeled to provide assistance in operations management of a manufacturing facility.
The Evolution of the MES
Before we discuss what an MES is and does, we need a brief history lesson on the use of computers in manufacturing. The late 1960’s saw the first steps of automated manufacturing processes away from electro-mechanical and pneumatic control and towards the use of computers. By the mid-1970’s the Computer-Integrated Manufacturing (CIM) automation revolution was in full swing. The development of manufacturing using digital microprocessor controlspawned software tools that allowed improved manufacturing design and control through use of process modeling and process segment control schemes. Computer integration also allowed the replacement of mimic busses and panel boards with graphic user interfaces. Local unit controllers were developed and the growth and standardization of digital communications connectivity allowed connected controllers to evolve into distributed control systems.
As computers became more common in manufacturing, the delineation of the different ‘levels’ of manufacturing were needed to provide a framework for optimal design, operation, control, and reporting. Figure 1 shows the CIM “pyramid”, a graphical depiction of enterprise work processes.
Figure 1: CIM Pyramid
MES concepts originated in the early 1980’s as computer data collection systems became more prevalent. In the middle 1980’s the Purdue Laboratory for Applied Industrial Control had an International Workshop on Industrial Computer Systems. This workshop formed a CIM Reference Model Committee culminating in a book published by the Instrument Society of America (ISA) in 1989. The book (known today as the Purdue Reference Model for CIM) provides a set of data flows, models, and function hierarchies for a generic manufacturing facility. The Purdue Reference Model for CIM addressed only those functions that either already were – or could someday be – automated. In the PRM for CIM, the Reference Model segments industrial control devices into hierarchical operational “levels” in a facility.
Figure 2: MES Functions
The Manufacturing Enterprise Solutions Association (MESA) is a manufacturing and production educational association that provides information, terminology, and models that help in mutual understanding and planning for increased performance across levels and disciplines within a manufacturing organization. In 1997, MESA developed a model defining eleven (11) functions that set the scope of an MES, shown in Figure 2. In early 2000, the ISA-95 standard merged the MESA model with the Purdue Reference Model (PRM). The merged model is shown in Figure 3.
Figure 3: ISA-95 CIM Levels
The merged-model hierarchical “levels” in a manufacturing facility are as follows:
Level 4 - The business-related activities needed to manage a manufacturing organization that are executed by enterprise-level software and systems to include:
• Plant scheduling - material use, delivery, and shipping
• Determining inventory levels
• Delivery of materials to the right place on time for production
Level 3 - The activities of work flow to produce the end products that are executed by the MES and MES-related systems.
Level 2 - The activities of monitoring and controlling the physical processes that are executed by the PLC, the HMI, and the Area and Unit Operations portion of the Supervisory Control and Data Acquisition (SCADA) system.
Level 1 - Activities involved in sensing and manipulating the physical processes executed by valves, sensors, motors, etc.
Level 0 - The actual physical processes
In Figure 2 we see the scope and functionality of an MES as imagined in 1997. ISA-95 took those basic MESA definitions and expanded them by adding activity tasks, and extended them into additional areas as well as into Maintenance, Quality, and Inventory. This “expanded” Level 3 is termed Manufacturing Operations Management (MOM). The remainder of this article will concentrate on Level 3 and the MES.
What is an MES?
An MES monitors and more efficiently controls plant operations. It helps to minimize downtime through real-time viewing of production and all its pieces. An MES coordinates the execution of recipes and records process data, alarms, and events from each production process segment.
Figure 4: ISA-95 Level 3 Activity Model
Figure 4 shows the ISA-95 Activity Model for Level 3. In effect, the MES is a series of applications residing on network servers that take their orders from Level 4 (Enterprise) in the form of recipes, schedules, and quotas and provide connectivity to Level 2 to tell the suite(s) or line(s) what to make, how much, and when. At the same time, the MES is monitoring the Production Level to assist in recording production data.
When MES systems were first introduced more than a decade ago, they were focused primarily on production and were under the domain of automation engineers. The first commercially available MESs were a subset of the ISA Level 3 MOM with a “these are the MES features, period” offering. The MOM is defined by ISA - 95 as a set of operational activities and MES the execution subset of those activities. Today, commercial MES packages have morphed into disparate - yet linked - modules and add-ons that support a wide variety of MOM activities and the line between MOM and MES is blurred.
The MES is used to bridge the gap between Level 2 (PLC/HMI) and Level 4 (enterprise). Where business decisions made at Level 4 can take months and years, information is gathered at Level 2 in seconds and minutes. There can be a real disconnect between these two hierarchical levels and the sheer volume of data gathered from Level 2 and generated and used at Level 3 can be overwhelming and unwieldy at Level 4. MESs can collect, collate, and parse manufacturing data to allow real-time or historical viewing and reporting of the data. The ability to take this manufacturing data and reconcile it with short- and long-lead business plans allows a manufacturer to improve business processes, achieve operational excellence, and hone a competitive market position. The key is to provide the right information to the right person so that the right decision can be made at the right time.
MES/MOM Application Offerings
We finish with a brief tour through MES implementation choices (plural here, since there are several groupings of MES building blocks that meet different needs within each facility MOM structure). Custom MES systems are currently in use throughout the world, but the trend is to purchase, configure, and customize standardized ISA compliant MES platforms. Using Figure 4 as a reference, MESs provide configurable building blocks used to create a system on a facility’s IT infrastructure.
The Production MES controls and coordinates manufacturing elements, material, equipment, personnel, specifications and procedures for Areas and Units within a facility. Module examples are:
• Product Definition Management
• Production Order Management
• Materials Management
• Plant Performance Analysis – Data collection necessary for Key Performance Indicators (KPIs) and Overall Equipment Effectiveness (OEE) calculations
• Detailed Production Scheduling
• Quality Assurance
• Laboratory Information Management (LIMS)
Research and Development (R&D) MES
The R&D MES communicates with, and integrates, Level 4 (business), R&D Level 2 (operations) and ancillary R&D-specific Units. Module examples are:
• Research Trial Management
• Laboratory Management
• Batch Record and Inventory Management
• Production Process Design
• Formula and Delivery System Development
• Quality Control
Additional MES Modules
MES Modules coordinate the ancillary and support activities in manufacturing. Module examples are:
• Operator/Engineer/Technician Training
• Materials Track and Trace
• Warehouse Management
The various modules, selections, and features of MESs available today allow users to be more selective in implementation, provide a business-related focus, and can integrate with already-installed applications. The challenge for any company looking to implement an MES in their facility is to effectively sort through the long list of available solutions.
ANSI/ISA–95.00.03–2005 - Enterprise-Control System Integration Part 3: Activity Models of Manufacturing Operations Management
A Reference Model For Computer Integrated Manufacturing (CIM) - A Description from the Viewpoint of Industrial Automation (Purdue Research Foundation – ISA, 1989)
MESA International Website: www.mesa.org