People performing office activities in plants make use of IT solutions and infrastructure that are common at all sites in the enterprise. Office workers use standard client personal computers (PCs) attached to the Office Automation (OA) network. These are primarily located in the office area of the plant and in workgroup meeting rooms near the shop floor. The OA network is available on the shop floor as well.
Programmable equipment, programmable logic controllers (PLCs), coordinate measuring machines (CMMs), material handling equipment, test stands and other devices exist throughout the shop floor, while mobile devices may be used in the yard around the plant. These devices connect to special-purpose industrial networks, which are segmented from the OA network for personnel safety and data security.
Each plant has a computer room operated as a small Data Center with a raised floor, multiple independent power sources, uninterruptible power supply (UPS), air conditioning and the like. Servers and other devices in the computer room are available to clients on the OA network and may be accessible from the specialized industrial networks on the shop floor. In some instances, the servers are purposely not accessible to clients on the OA network.
Plant Floor Device Integration
For existing equipment and process controls, an OPC (an open communication standard) server may be used to convert data communicated from devices using proprietary protocols into standard messages for communication with transactional applications. Over time, eXtensible Markup Language (XML) Web Services as defined by the Web Services-Interoperability organization (WS-I), using the latest security and reliable messaging specifications, may be used to integrate with controls. The OPC Foundation has defined a new specification along these lines called “OPC Unified Architecture” (OPC UA). Using Web Services and OPC servers enables the infrastructure as a whole to be refreshed, common and standard while supporting a wide variety of shop-floor technologies.
A logical view of the manufacturing supply chain shows the enterprise
separated into various layers (corresponding to the Instrumentation,
Systems and Automation Society’s ISA95 Enterprise Domain Hierarchy) of
the business: Shop Floor, Plant Computer Room (Office Automation),
Plant or Enterprise Manufacturing Operations Management “de-militarized
zone” or DMZ, Enterprise Data Center, Extranet, Internet DMZ and
Internet. The logical separation between the layers is either a
communication bus or a firewall with a communication bus connecting all
layers and a firewall between the appropriate layers. The various
communication buses may be one physical implementation or several
implementations. The separation shown in the figure is used to specify
the type of communication used at a particular layer. For instance, at
the device communication layer, OPC and other types of architecture
(i.e. sockets) exist for communicating between devices such as PLCs.
Level 4 controls and monitors inventory levels and also establishes the basic plant schedule—production, material use, delivery and shipping. System time frames are in months, weeks and days.
Level 3 establishes work unit definition and control, in the form of workflow/recipe control, to produce desired end products. Manufacturing Operations Management (MOM) systems including Manufacturing Execution Systems (MES) analyze work data, maintain records and optimize the production process. System Time Frame is in days, shifts, hours, minutes and seconds.
Level 2 defines the work unit (operation). Systems monitor and provide supervisory control and automated control of the production work process. System Time Frame is in hours, minutes, seconds and micro seconds or less.
Level 1 defines the sensing and manipulating of production work process. Device Time Frame is in real-time; in micro seconds or less.
Level 0 defines the shop floor through the actual production physical process.
Gary Mintchell, email@example.com, Editor in Chief of Automation World, adapted this article from the MESA International (www.mesa.org) white paper, “SOA in Manufacturing Guidebook.”