In the modern manufacturing landscape, an integrated system based on the ERP/MES/PCS three-tier architecture is widely used to enhance operational efficiency and data flow across different levels of production. As depicted in Figure 1, the ERP system focuses on enterprise-wide resource optimization, particularly through financial analysis and decision-making. The MES (Manufacturing Execution System) bridges the gap between planning and execution, managing production processes with a focus on real-time monitoring and control. Finally, the PCS (Process Control System) ensures equipment-level integration and control, making it essential for achieving full automation within an enterprise.
There are three primary methods for an application to access process control devices: the driver method, the DDE method, and the OPC method. The driver method, as shown in Figure 2, involves a direct connection between software applications and devices, but this approach requires a large number of drivers—M×N for M applications and N devices—which can lead to complex structures and high development costs. The DDE (Dynamic Data Exchange) method, illustrated in Figure 3, offers a simpler setup but suffers from slow data transfer speeds, limited flexibility, and poor reliability, making it unsuitable for distributed environments. In contrast, the OPC (OLE for Process Control) method, demonstrated in Figure 4, simplifies the integration by allowing any device to connect to any system via a single driver, resulting in faster communication, lower development effort, and higher reliability.
OPC technology has evolved significantly over the years. Initially based on COM/DCOM, it provided a standardized interface for process control and manufacturing automation. This client-server model allowed hardware vendors to package their device drivers into servers that continuously supply data to OPC clients. Developers could then write applications without worrying about the underlying hardware, enabling seamless integration across multiple systems. The OPC standard includes specifications for real-time data access, alarms, historical data, and security, ensuring comprehensive support for industrial applications.
With the rise of web technologies, the OPC Foundation introduced OPC XML, which leverages XML for data exchange. This new approach enables more flexible and platform-independent communication, supporting web-based applications and cross-platform interoperability. While OPC COM/DCOM remains popular due to its speed and performance, especially in factory LANs, OPC XML offers greater scalability and compatibility with modern enterprise systems. However, transitioning fully to OPC XML may take time, as many existing systems still rely on COM/DCOM for efficient operation.
Modern MES systems now face new challenges, such as integrating process information over the internet and handling multi-operational environments. Traditional MES solutions have successfully utilized OPC COM/DCOM for local network integration, but enterprises now demand more advanced capabilities. The ability to transmit shop floor data beyond the firewall and integrate it across the internet is becoming increasingly important. Additionally, the coexistence of legacy systems within organizations presents a challenge for seamless data flow and integration.
As shown in Figure 5, the use of OPC-based approaches allows for better connectivity and flexibility in MES implementation. While OPC XML DA Web services offer promising solutions for enterprise-wide automation, the transition from traditional COM/DCOM systems will be gradual. For applications requiring high performance, OPC COM/DCOM will continue to play a vital role, while those focused on broader connectivity can benefit from OPC XML's features.
The overall architecture of an OPC-based MES system, illustrated in Figure 6, highlights how these technologies work together to enable efficient and scalable process integration. As industries continue to evolve, the combination of OPC COM/DCOM and OPC XML will remain key to achieving seamless automation and information sharing across the entire enterprise.
Zgar International (M) SDN BHD , https://www.zgarvape.com