Since the birth of the first PLC in 1969, PLC has become the apple of the eye of the industry. After nearly half a century of development, PLC has become the core component of industrial automation system. In the intelligent era of industrial transformation and upgrading, PLC not only meets the control function, but also has data analysis, process optimization, network security protection, fault prediction and other functions, completing the transformation from classic control to intelligent control.

1. Development and application of traditional PLC

1.1 development and application history of international PLC

PLC, also known as programmable logic controller, is RichardE.Morley It was invented in 1968. Its core design idea is to use software programming instead of hardwired relay control to build program control system. In the same year, general motors developed the design standard of PLC. Since then, PLC has been widely used in various industrial fields.

The 1970s is the rising period of PLC. Since Rockwell Automation first proposed PLC based on 8-bit microprocessor in 1977, many manufacturers have imitated and produced PLC products based on 8-bit microprocessor, such as Intel 8080 and zlog Z80.

In the 1980s, with the development of microelectronics and microprocessor technology and the application of PC, PLC technology is in a mature stage. Athani designed a PLC based on 8-bit microprocessor 8085, which has a manual programmer and CRT display terminal, and program segments can be displayed on CRT.

In the 1990s, with the formal promulgation of the international standard IEC61131, PLC technology has entered the third development period. At this time, the development of the system structure from the traditional single processor to the multiprocessor, the development of the control system configuration from the independent control system to the distributed and remote control system, and the programming language tends to be diversified and mutually transformed. In addition to the automatic production line, PLC based distributed control system (DCS), supervisory control and data acquisition system (SCADA), flexible manufacturing system (FMS), safety interlock protection (ESD) system, motion control system, etc. are developed to improve the application scope and level of PLC in all aspects.

Since the end of 1990s, due to the rapid development of information technology and users’ strong demand for openness, open communication interface is adopted for fieldbus network on the premise of retaining PLC function. Gradually break the closed state of each PLC product, adopt the relevant international industrial standards, so that the application developed by users can be transplanted to different PLC products.

To sum up, since the advent of PLC, it has always shown strong vitality and rapid growth. At present, there are more than 200 PLC manufacturers in the world, as well as thousands of kinds of products.

1.2 development and application history of PLC in China

In China, since 1970s, the research and application of PLC have been started in China. In 1974, China first copied the second generation PLC produced in the United States. In 1977, China successfully developed the first PLC with practical value in China by using mc14500 integrated chip of Motorola Company. In 1979, the PLC of Modicon 584 imported from the United States was first successfully applied in the auxiliary equipment of power station.

In the early 1980s, while actively introducing foreign PLC production lines, China developed some of its own PLC products, which greatly improved the reliability and gradually gained the recognition of users.

It is understood that the total demand of the domestic PLC market is large, and the domestic PLC accounts for a very small share of the whole market. The reasons for the backwardness of the domestic PLC are as follows: first, technical problems, lack of openness; second, lack of a large amount of funds, no scale; third, the manufacturing process needs to be strengthened; fourth, the urgent need to enhance competitiveness and form a brand. Therefore, we should concentrate capital and technology to develop a series of products with independent property rights. In particular, we should seize the opportunity of the era of intelligent manufacturing, make full use of the advantages of the era of continuous improvement of software and hardware performance, and develop professional, high-performance and intelligent PLC for big data.

2. In the era of intelligent manufacturing, the new demand and new foundation for the development and application of PLC

2.1 new requirements of PLC Development

2.1.1 in recent years, the market development of PLC puts forward new requirements for PLC

According to the global PLC market report released by Frost & Sullivan, PLC market is developing actively in many fields. It is estimated that the installed capacity of PLC is currently 52 million units, of which micro PLC accounts for a considerable number. It is expected to reach 65 million units by 2019, most of which will be replaced. Replacing the existing PLC in the next five years will be an important factor in the growth of PLC market. Due to the rapid popularization of industrial Internet of things and the gradual entry of cloud services into the industrial market, PLC needs to be directly connected with MES, ERP and other upper management software information systems. PLC system must meet the requirement of intelligent manufacturing of hardware and software. As a part of industrial Internet of things, PLC becomes more and more important as edge computing. Deploying PLC as the first layer computing function close to devices or processes can achieve intelligent or coordinated event response, and help reduce the data processing burden of cloud. In a system with dozens, hundreds or even thousands of sensors, most of the data from these sensors may not be of much value and only report “normal” operating conditions. PLC can filter, discard or more effectively reassemble data for transmission to the cloud for storage and analysis. When a critical event occurs, PLC can quickly determine the correct response, issue appropriate instructions to the connected devices, and summarize the events in a report suitable for cloud use.

2.1.2 the demand of complex control puts forward new requirements for PLC function

In the field of machine control, some PID adjustment and process algorithm similar to process control are needed, and PLC is required to have excellent algorithm design and processing ability; motion control is more widely used, PLC needs to meet the requirements of electronic gear, electronic cam and positioning control, and develop products with safety and equipment safety requirements. In order to meet the complex path planning and matrix transformation of robot, it is necessary to integrate CNC and robot library into PLC.

2.1.3 the demand of big data puts forward new requirements for PLC function

More and more sensors are used to monitor the environment, the health status of equipment and various parameters of the production process. The effective collection of these industrial big data forces PLC to adopt embedded PLC and complete the increasingly complex field as much as possible, which greatly improves the seamless connectivity. The relevant control parameters and equipment status can be directly transmitted to the upper system and application software, or even sent to the cloud .

2.2 new foundation of PLC Development

2.2.1 requirements of PLC hardware assisting intelligent manufacturing

2.2.2 requirements of PLC software assisting intelligent manufacturing

In order to solve the problem that different software is used in the engineering design, programming, operation and management of PLC control system, which leads to the inconsistent naming of the same object, PLCopen international is committed to cooperating with many international standardization organizations and foundations to develop the information model of IEC61131-3, opcuaclient FB and opcuaserver FB, and to establish an open standard ecosystem.

2.2.3 requirements of IT technology for intelligent manufacturing

With the development of IT technology, CPU processing power, communication speed, storage and expansion ability, software function block (OPC), diagnosis and maintenance ability and display ability have been greatly improved, and the development of IT technology also brings about the continuous decline of hardware cost.

3. The new trend of PLC Development in the era of intelligent manufacturing

3.1 continuous enhancement of performance index

With the development of IT technology, the performance index of PLC has changed from speed to safety, stability and reliability, communication ability, motion control ability, real-time communication ability, data processing ability, process optimization ability and fault diagnosis ability.

3.2 continuous enhancement of network support capability

With the improvement of field equipment intelligence and the need of control system to ensure reliability, stability and availability, network coverage ability directly determines the control level of field process equipment. Therefore, PLC will enhance the ability of interface support from bus, Ethernet, real-time Ethernet and other aspects. Ethernet higher speed data transmission meets the application of video data, visual recognition, image processing and other industrial data transmission. The real-time Ethernet meets the data exchange capacity requirements of robot, CNC, motion control and safety high-speed synchronous control. Its data refresh speed is in μ s level, and the synchronization accuracy is 0.1 μ s.

3.3 continuous enhancement of software support capability

In order to complete the intelligent control, the software development platform must have a high-level language supporting complex algorithms. High end PLC uses RTOS to improve real-time processing and support multi task processing. In order to realize the unified programming and security of logic and motion control, PLCopen standardizes the support of program interface and custom library.

3.4 increasing security technology

“One network to the end” after the whole network is connected, the on-site production process equipment and the above management software and even the cloud are connected together, the requirements for information security are higher, so we must follow the IEC61508 standard and strengthen the research on Safety PLC and bus safety.

3.5 continuous enhancement of software platform integration

The integrated platform represents the ability to provide the overall solution. Through the integration of basic PLC technology, HMI technology, motif technology, sensor technology and bus technology, it provides the service ability of PLC with full product life cycle functions including programming, simulation, testing, maintenance and diagnosis, so as to provide value for customers.

3.6 continuous enhancement of industry standards

IEC / PLCopen integrates plcopenlogic, XML, safety, motif, hydraulic, IEC61131-3 and other standards, and can easily develop software applications based on these libraries. Universal standard Unicode can meet the multi language support library of the system, ensure that PLC products can support all kinds of languages all over the world, so that the products can be sold all over the world. In order to be able to connect with the upper SCADA and the ERP system of the management layer, Microsoft and other automation manufacturers jointly developed OPC servers for different PLC connections to ensure the connection with the management system.

3.7 the ability of information processing is constantly enhanced

In intelligent manufacturing system, PLC is not only controller, but also collector and repeater. Only by using the function of SOA can PLC accomplish these important tasks. Soaplc actually puts the web service of virtual private network (VPN) supporting information security into PLC. The service authority performs object-oriented data communication, including real-time data and historical data, alarm data and other services. Through these services, PLC will connect the corresponding large amount of data to the superior service and data layer, so as to model and use the information model. It allows PLC to integrate opcua’s server function and opcua’s client function to ensure that PLC can perform secure data communication through VPN.

3.8 continuous enhancement of user experience performance

In the future, all devices will connect intelligent development, field devices and field instruments directly to the control system through Ethernet. The screen of the monitoring system will become very large, but the equipment should be as small as possible to improve comfort and efficiency. This needs to solve EMC interference, solve the problem of heat dissipation, solve the problem of circuit layout, and achieve a more powerful controller in a smaller space.

3.9 continuous enhancement of professional quality ability

In order to reduce the production and manufacturing costs of the system, PLC products continue to move towards modular and standardized design. Due to the generalization and standardization of hardware, the cost of the system is reduced, and in order to seek the competitiveness of differentiation, high-end PLC will pay more attention to the development of software function and industry application library, and the more subdivided market makes the application differentiation become a competitive weapon.

Editor in charge: yyx

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