MES process information integration framework based on OPC technology

A modern integrated manufacturing system model based on the ERP/MES/PCS three-tier architecture is shown in Figure 1. The ERP system uses the financial analysis/decision as the core of the overall resource optimization technology, emphasizing the planning of the enterprise; the MES system uses the production of comprehensive indicators as the target of the production process optimization control, production operation optimization operation technology, emphasizing the implementation of the plan; PCS The system takes the equipment integrated management control as the core technology and emphasizes the control of the equipment. To achieve integrated enterprise automation (ie, management and control integration), the production execution system MES in the middle layer is indispensable.

Figure 1 ERP / MES / PCS three-tier architecture integrated manufacturing system

There are three ways for an application to access a process control device:

(1) Driver method, as shown in FIG. 2, using M application software, N devices, the number of drivers is M×N. The downside is that the structure is complex and developers spend a lot of effort developing drivers.

Figure 2 Driver Method

(2) The DDE method, as shown in Figure 3, is not too complicated, but requires a dedicated DDE to export the linked list. The disadvantage is that the data transmission speed is slow, the function lacks flexibility, the reliability is unsatisfactory, and it is not suitable for distributed applications.

Figure 3 DDE method

(3) OPC method, as shown in Figure 4, any device only needs to provide a driver for any software system. Compared with the other two methods, the advantages are simple structure, small development workload, fast data transmission speed and high reliability.

Figure 4 OPC method

OPC technology and its development

OPC COM/DCOM technology

Generally referred to as OPC (Ole for Process Control) technology is OPC-COM / DCOM technology, based on Microsoft's COM, DCOM technology, provides a common interface set for process control and manufacturing automation software module exchange And sharing data allows users to care about the details of control software and devices in process control during system development, providing users with an open and flexible plug-and-play software solution with minimal hardware and software Supplier development and maintenance costs.

The OPC COM/DCOM standard uses a client/server architecture that requires all hardware vendors to package hardware device drivers into separate servers that are responsible for continuously providing data to the OPC client. Application developers can rely on OPC requirements. Write the program code in any language. As the OPC client, the upper application can not contain any communication interface program, do not care about the underlying hardware device characteristics, and do not need to consider how the hardware and software communicate. As long as the data interface protocol is followed, the data can be retrieved from the data server, so that the data can be realized. Flexible configuration and true integration of multiple systems.

The OPC COM/DCOM standard mainly includes real-time data access interface specification, Alarm and Event Interface specification, historical data access interface specification, security specification (OPCSecurity), OPBCatch and OPC Data Exchange, etc. The real-time data access interface specification is for real-time data processing; the alarm and event interface specification is for highly sensitive real-time data; the historical data access interface specification is for data for trend display, historical analysis, and reporting.

OPC XML technology

With the development of Web technology, Web services provide a broader prospect for the further development of OPC technology. Web services are new platforms for creating interoperable distributed applications. The main goal is cross-platform interoperability. Web services are completely independent of platform and software vendors based on XML, and the new generation of Web Programming is widely defined in XML Web Services, enabling it to implement Web-based distributed computing and processing.

In recent years, XML has become a popular data encoding and exchange format due to its openness and system independence. Corresponding to the existing OPC-COM interface, the OPC Foundation chose XML as the enabling technology for accurate data transmission.

New requirements for MES process information integration

Traditional MES has successfully used OPC COM/DCOM to integrate shop floor LAN process information. However, with the further deepening of enterprise informationization, modern MES has created new requirements for OPC in the following two aspects:

(1) Internet-based process information integration Traditional MES is integrated in the enterprise LAN. However, with the development of the Internet, enterprises require MES to pass the enterprise process firewall to transmit the process information of the workshop, which can be further extended through the Internet. The ability to build enterprise applications based on Internet integration.

(2) Process information integration in multi-operational environment Due to the difference between the historical “legacy system” and the implementation of enterprise informationization, there is a common phenomenon of multi-operational environment coexisting within the enterprise, which limits the process of enterprise process information integration to a certain extent. It has become a huge obstacle for enterprises to achieve information connectivity.

Through a comprehensive understanding of OPC technology, we can know that OPC technology has greatly promoted the development of enterprise automation , especially the emergence of OPC XML DA technology, which enables OPC to pass through the enterprise firewall friendly and support more. A multi-platform and computing environment provides a new way to solve problems.

Figure 5 OPC-based MES approach

However, as a new technology, its widespread promotion requires more support from OPC XML servers. Currently, it is unrealistic to require thousands of OPC COM/DCOM servers to be completely modified or launched. . In fact, many current OPC COM/DCOM servers run very well at the shop floor, and DCOM execution is faster than Web services, and OPC XML execution efficiency needs to be further improved, which makes the OPC COM/DCOM server mandatory. It will continue to exist for a long time and will not be eliminated immediately.

Currently, for applications that focus on speed, efficiency and effectiveness, especially in factory LANs, most existing OPC COM/DCOM applications will continue to use OPC COM/DCOM technology for a certain period of time. For the needs of enterprise information development, it is possible to expand its Web service interface; for those places where enterprise connectivity is its main goal and execution efficiency is not high, the OPC XML DA Web service will provide good development for enterprise automation. Technical support.

Figure 6 OPC-based MES overall architecture