In a modern integrated manufacturing system, the ERP/MES/PCS three-tier architecture plays a crucial role. As illustrated in Figure 1, the ERP system focuses on enterprise resource optimization through financial analysis and decision-making, emphasizing strategic planning. The MES system, located in the middle layer, optimizes production processes using comprehensive indicators, ensuring efficient execution of plans. Meanwhile, the PCS system centers around equipment integration and control, enabling precise management of industrial machinery. To achieve full-scale enterprise automation—where both management and control are seamlessly integrated—the MES is essential.
There are three primary methods for an application to access process control devices: the driver method, DDE (Dynamic Data Exchange), and OPC (OLE for Process Control). The driver method, as shown in Figure 2, requires a separate driver for each software-device combination, resulting in a complex structure and high development costs. The DDE method, depicted in Figure 3, simplifies the process but suffers from slow data transfer speeds, limited flexibility, and reliability issues, making it unsuitable for distributed applications. In contrast, the OPC method, illustrated in Figure 4, offers a more streamlined approach where any device only needs one driver, allowing multiple systems to access it efficiently. This method provides faster data transmission, greater reliability, and reduced development effort.
OPC technology, specifically OPC COM/DCOM, is widely used in industrial automation. Based on Microsoft’s COM and DCOM technologies, it offers a standardized interface for exchanging and sharing data between process control and manufacturing software modules. This allows developers to focus on application logic rather than device-specific details. The client/server architecture enables hardware vendors to package their drivers into servers that continuously supply data to OPC clients. Developers can then write applications in any language, without needing to handle communication protocols or device characteristics. This makes integration flexible and cost-effective.
The OPC standard includes several key specifications, such as real-time data access, alarm and event handling, historical data retrieval, and security features. These ensure reliable and efficient data exchange in industrial environments. With the rise of web technologies, OPC XML emerged as a new solution, leveraging XML for open, platform-independent data exchange. This has enabled OPC to support internet-based integration and multi-platform environments, offering a more scalable and interoperable solution.
Modern MES systems now face new challenges, such as integrating process information across the internet and managing diverse operational environments. Traditional MES systems were confined to local networks, but today’s enterprises require seamless connectivity beyond firewalls. Additionally, many organizations still operate with legacy systems, creating a multi-operational environment that complicates integration efforts. OPC technology, especially OPC XML DA, helps overcome these barriers by supporting secure, cross-platform data exchange.
Despite the benefits of OPC XML, the transition from traditional OPC COM/DCOM is gradual. Many existing systems perform well in factory LANs, and DCOM remains faster for certain applications. However, OPC XML offers promising potential for enterprise-wide automation, particularly where web-based integration is a priority. While the future may see a shift towards OPC XML, the legacy systems will continue to play a role for the foreseeable future.
As shown in Figures 5 and 6, the OPC-based MES architecture supports both traditional and modern integration approaches, ensuring compatibility and scalability. For businesses looking to enhance efficiency and connectivity, a hybrid model that combines OPC COM/DCOM with Web services can provide a balanced solution. This ensures that existing infrastructure is not discarded, while also paving the way for future advancements in industrial automation.
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