XML format of IEC61131-3 and its application
With the widespread acceptance of the IEC 61131-3 standard and the increasingly fierce economic competition, coupled with rising development and engineering costs for industrial control software, the demand for exchanging programs, function/function block libraries, and engineering projects between different software development environments is growing. Considering that programming is only one part of a complete application development kit for control software, it is necessary to provide a data exchange specification for implementing IEC 61131-3 programming to standardize the data exchange interface between it and other components. By specifying an XML format for IEC 61131-3, a development environment is advocated, enabling the construction of a unified engineering software platform on this basis.
By utilizing the XML format of the PLCopen specification, data exchange between different software tools can be achieved: providing a foundation for programming and configuring different control functions on a unified engineering platform; providing a foundation for seamless integration of functions across the design, debugging, operation, and maintenance stages of a unified engineering platform; and enabling direct transformation of I/O variables and internal variables defined by different hardware platforms, creating preconditions for the unimpeded portability of control programs. Information including text-based programming languages, graphical programming languages, structured programming languages, graphical information, and data types can all be expressed in XML format.
For example, initiated by the German automaker Daimler, and joined by industrial companies such as ABB, KUKA, Rockwell Automation, and Siemens, as well as some software and service providers, the AutomationML (Automation Markup Language) organization was established. Its purpose was to define and standardize AutomationML, an intermediate format for digital factories. The AutomationML standard is a free and open standard, primarily used for manufacturing automation, including robotics and logistics, but not limited to these. Its innovation lies mainly in integrating and applying many accepted standards from important engineering aspects under a single root format (XML format).
IEC61131-3 OPCUA Information Model
The purpose of establishing the OPCUA information model of IEC 61131-3 is to improve the reusability of communication between controllers, visualization devices (human-machine interfaces), and higher-level information systems. From a long-term application perspective, this will significantly improve the efficiency of engineering processes and substantially reduce engineering costs. Imagine a PLC project with many control platforms provided by different vendors. If a single visualization tool or MES/ERP is used, from the outside, these control platforms appear completely identical. PLCopen chose OPCUA because its unified architecture solves the following problems: how to discover communicating objects at the monitoring level; how to ensure the data, complex data, and functionality of communicating objects are fully available; how to make communication reliable, executable, and independent of operating systems and programming languages; and how to ensure information security.
Physical demonstrations of the IEC 61131-3 information model using OPC were exhibited by multiple suppliers at the SPS/IPC/Drives trade fair in Nuremberg, Germany in 2009, the HMI trade fair in 2010, and the Lighting and Building trade fair in 2010.
Development Trends and Potential of Embedded PLCs
According to a survey by ControlDesign magazine, in 2009, PLC users accounted for two-thirds of the US machinery industry, PAC and PC controls combined accounted for only 13%, and embedded PLCs accounted for only 5%. This indicates that embedded PLCs have great potential for development.
Currently, the development of embedded PLCs is also diversified, with good performance both domestically and internationally: the netPLC launched by HISHUAN in Germany, which combines fieldbus technology and PLC technology, is very distinctive.
Several years ago, Huazhong University of Science and Technology in China loaded embedded PLC system software into the EASYCORE 1.00 core chipset as a hardware platform and developed a multi-mode input channel embedded PLC. Another development path is to develop a hardware/software integrated platform that combines PLC with human-machine interface. This fully utilizes CASE tools, combines development platforms of various embedded chips and hardware circuit libraries of various input/output channels, and develops customized, ODM-like special PLCs for electromechanical equipment.
Embedded PLCs have broad development prospects in my country, primarily because they are well-suited to leveraging two key characteristics of my country's automation industry: a robust market base for supporting electromechanical equipment and a sufficient number of globally competitive design and development teams. We can completely replace general-purpose PLCs with embedded PLCs designed and manufactured to meet customized requirements at the lowest cost and with high quality.
Meanwhile, embedded PLCs offer flexible and customizable hardware, software, human-machine interface, and communication functionalities, better meeting the requirements of various levels of electromechanical equipment. Based entirely on embedded system technology, embedded PLCs are readily available. Their advantages, such as SoC chips, embedded operating systems, and programming environments conforming to the IEC61131-3 programming language standard, make them readily available in the market.
Developing general-purpose PLCs is not technically difficult in the current environment, but seizing market share requires significant financial and human resources. In today's market, where a few large companies have firmly established their dominance, pursuing this approach seems inefficient. However, the promising progress made in my country's small-scale PLC development in recent years further validates this assessment.
