Computer control system

System composition

Computer control system is a system that uses computers (usually called industrial control computers) to realize automatic control of industrial processes. In the computer control system, since the input and output of the industrial control machine are digital signals, the signals collected on site or sent to the actuator are mostly analog signals, so compared with the conventional closed-loop negative feedback system controlled by deviation , The computer control system needs to have two links of digital/analog converter and analog/digital converter.

The computer directly feeds back the digital signal sent by the measuring element, the transmission unit and the analog-to-digital converter to the input terminal for comparison with the set value, and then performs calculations according to the deviation according to the requirements, and the obtained digital The output signal is sent to the actuator through the digital-to-analog converter to control the controlled object and stabilize the controlled variable at the set value. This kind of system is called a closed-loop control system.

Computer control system is composed of industrial control machine and production process. Industrial control machine hardware refers to the computer itself and peripheral equipment. The hardware includes computer, process input and output interface, man-machine interface, external memory, etc. A software system is the sum of computer programs that can complete various functions, usually including system software and application software.

The range of accused objects is very wide, including production processes, mechanical devices, vehicles, robots, experimental devices, instrumentation, household living facilities, household appliances and children's toys in all walks of life. The purpose of control can be to make the state or movement process of the controlled object meet a certain requirement, or to achieve a certain optimization goal. Computer control systems usually have the characteristics of high accuracy, high speed, large storage capacity and logical judgment function, so they can realize advanced and complex control methods and obtain fast and precise control effects. The development of computer technology has caused considerable changes in the entire human society, and naturally it has also been applied to industrial production and business management. Moreover, the information processing capabilities of computers can further organically combine process control and production management (such as CIMS), thereby realizing comprehensive automated management of factories and enterprises.

Same as the general control system, the computer control system can be closed-loop. At this time, the computer must continuously collect various status information of the controlled object. After processing according to a certain control strategy, the output control information directly affects the Control object. It can also be open-loop, and there are two ways: one is that the computer only affects the controlled object in chronological order or a given rule; the other is that the computer only processes the information from the controlled object. Provide operation guidance information to the operator, and then manually influence the accused object.

The computer control system is composed of a control part and a controlled object, and its control part includes a hardware part and a software part, which is different from a system composed of an analog controller only composed of hardware. Computer control system software includes system software and application software. System software generally includes operating systems, language processing programs and service programs, etc., which are usually matched by computer manufacturers for users and have a certain degree of versatility. Application software is a special program compiled for specific control purposes, such as data acquisition program, control decision program, output processing program and alarm processing program. They involve the characteristics and control strategies of the controlled objects, etc., which are compiled by the professionals who implement the control system.

Formation and development

Ignoring the quantization effect of digital signals, the computer control system can be regarded as a sampling control system. In this system, the continuous links are discretized, then The whole system can be regarded as composed of different discrete systems. The development of computer control theory is mainly to integrate sampling theory, difference equation, transformation theory, state space theory and system identification adaptive control theory into the control technology, so that the computer control system has a preliminary development. For complex and time-varying nonlinear systems, the control system incorporates many new theories such as robust control, fuzzy control, and predictive control, gradually forming a new direction for industrial process control systems.

Since the world's first electronic computer came out, the computer was first used to automatically detect the process parameters of the chemical production process and carry out related data processing. At the same time, the open loop control of the computer was also studied. By the 1960s, computers for process control appeared, realizing direct digital control. Later, the centralized computer control system developed to a layered control system with a microprocessor as the core, and the production process was centrally monitored, operated, and managed through the computer. With the development of computer processors and other technologies, computer control technology has also undergone corresponding changes, which are finally applied to industrial production and have a huge impact on it.

Development and status quo

In many fields such as production and scientific research, there are a large number of physical quantities that need to be controlled according to a certain change law. Before the 1930s, industrial production was mostly manual. At first, base-type instruments were used to control pressure and temperature within a constant range, and the mechanical control practice for industrial production was initially established. With the rapid development of electronic technology and the emergence of computer control systems, the digital control of various parameters and processes in industrial production has been directly realized. The miniaturization of computers has made the control technology more intelligent. At the same time, the mechatronics technology, which organically combines mechanical, electronic, computer technology and control technology, has also developed rapidly, and is more and more widely used in various production fields. At present, the main electromechanical control technology that has been formed and applied is PID control. PID is the representative of classic control theory. It absorbs intelligent control ideas and uses the advantages of computers to form adaptive PID and nonlinear PID, which are more conducive to control variants. Controller. In addition, there are fuzzy control (FLC), variable structure control, etc., which are constantly expanding with the development of the computer field.


Introduction and production application of mechatronics

Mechatronics refers to the main function and power function of the mechanism , Information processing function and control function, the introduction of electronic technology, the general name of the system constituted by the integration of mechanical devices, electronic design and computer software Supervise the operation of the control process in the field. Its main application areas are numerical control machine tools. Through the corresponding numerical control technology, the structure, function, and operation accuracy of industrial operations have been significantly improved. The use of a multi-CPU and multi-mainline architecture enriches the CNC functions and improves production efficiency.

The application of flexible manufacturing system is the application of computer technology and manufacturing system in the electromechanical control industry, and it is a computerized manufacturing system. It is mainly composed of computers, CNC machine tools, automated warehouses, etc. In industry, it can randomly and quantitatively produce any workpiece within its capacity according to the requirements of the assembly department. It is more suitable for the mass production of discrete parts of multiple varieties and small batches.

The development of AC drive technology also has important applications in industry with the development of electronic technology and computer technology, especially in the iron and steel industry, enabling the realization of complex vector control technology, whether it is large Both the capacity motor and the small capacity motor can now realize the reversible sliding speed regulation of the synchronous motor or the asynchronous motor. It also makes the AC drive system widely used in steel rolling production.

Programmable controller (PLC) is a new type of control system that integrates computer technology and automatic control technology. This system solves the problem of a large number of switch control in the industrial control system, and gradually replaces the relay control system that consumes a lot of energy and has a high failure rate. With the advancement of PLC technology, its application fields are constantly expanding. It can collect and store data, and can also monitor the control system. PLC can compile various control algorithm programs to complete closed-loop control. This kind of process control is widely used in metallurgy, chemical industry, heat treatment, boiler control and other occasions. In addition, with the development of factory network automation, PLC can realize communication and networking functions, which is more conducive to the monitoring of the control process of industrial production. Today, PLC technology has been widely used in various industries such as metallurgy, petroleum, chemical industry, building materials, machinery manufacturing, electric power, automobiles, light industry, environmental protection, culture and entertainment.

Application examples of computers in the machinery and electronic control industry

The organic combination of computer technology and the integration of mechanical and electronic control technology continues to make relevant new technologies Applied to more fields, these fields of application are no longer limited to industrial production, and more technologies are closely related to our daily work and life. Here are a few specific examples to introduce the practical application of the combination of computer technology and electromechanical control.

PLC realizes the control process of manipulator moving workpiece. With the development of the world economy and technology, the scope of human activities continues to expand, and the application of robots is rapidly expanding to various fields of social production and life, and from the manufacturing field to the non-manufacturing field, a variety of robot products appear. . With the production and large-scale application of robots, in many fields, many single and repetitive mechanical tasks are completed by robots (also called manipulators). Industrial robot is an automatic control, reprogrammable, multi-functional, multi-degree-of-freedom, and multi-purpose manipulator. Industrial robots are widely used, which can not only improve product quality and output, but also ensure personal safety. It is of great significance to improve the labor environment, reduce labor intensity, increase labor productivity, save raw material consumption and reduce production costs. The widespread use of industrial robots combined with computer and network technology is increasingly changing the production and lifestyle of human beings.

In agriculture, the instrument panel in the cab during mechanical operation is rapidly being replaced by electronic monitoring instruments and gradually transitioning from a single parameter display mode to an intelligent information display terminal to improve the human-computer interaction interface. This kind of intelligent display terminal is also called Virtual Display Terminal (Virtual Display Terminal), which represents the mainstream direction of the development of contemporary instruments and control devices. It can arbitrarily select and display terminal information of different parts of the unit through the screen, call database information according to the needs of the operator on the screen, and display multimedia information such as data, graphics, and voice. In addition, the data information can be dynamically stored in a high-density intelligent data storage card similar to the size of a credit card, and the data information of the agricultural operation process can be brought back to the office through the smart card and processed by the computer application of advanced software. The decision and operation instructions of the manager can also be transmitted to the intelligent control terminal on the tractor through the smart card to realize the automatic control of the operation of the agricultural machinery.

The application of PLC in vending machines. The automatic vending machine selects the product switch through the customer, and the value of the coin is displayed by the PLC driven digital tube. After the light sensor is identified, the next step is performed through the judgment, and the sales process is completed through the PLC system control and signal output. The application of computer technology and electromechanical automatic control in vending machines greatly facilitates people's lives and makes the application of PLC more extensive.

Traffic signal lamp system is also a typical example of microcomputer software applied to electronic control system. Mainly apply PLC technology to control the action of signal lights at intersections. Accurately complete the signal light changing action to control the time, this application is greatly convenient for people's daily work travel.

The application of computer technology in computerized flat knitting machines has brought tremendous changes to the mechanical knitting industry. Computerized flat knitting machine is a complex system involving computer, machinery, electronics, control and many other fields. The knitting of a computerized flat knitting machine is an extremely complicated process. The original flat knitting machine was a manual flat knitting machine, which was only capable of a relatively simple knitting process. With the application of computer technology to the computerized flat knitting machine, through the automatic control of the computer, the designer can digitally design the knitting pattern, and directly control the machine's unwinding, sanding, unwinding, sand bending and other corresponding machinery through the computer digital The knitting action is completed by the computer command control system to complete the knitting of the entire design, which greatly improves the industrial production efficiency.

There are still many technologies related to mechatronics, and with the development of science and technology, the trend of integration of various technologies will become more and more obvious. The main body's mechatronics technology is an inevitable trend in the development of the machinery industry.

Application type

Data acquisition system

In this application, the computer only undertakes the work of data acquisition and processing, and Not directly involved in control. It conducts round-robin detection, processing, recording and over-limit alarm of various process variables in the production process. At the same time, it conducts cumulative analysis and real-time analysis of these variables, and obtains various trend analysis to provide references for operators.

Direct digital control system

The computer performs calculations according to the control law, and then passes the result through the process output channel to the controlled object, so that the controlled The variable meets the required performance index. The difference from the analog system is that in the analog system, the signal transmission does not need to be digitized; while the digital system must first perform analog-to-digital conversion, and the output control signal must also perform digital-to-analog conversion before driving the actuator. Because the computer has strong computing power, it is very convenient to change the control algorithm.

Because the computer directly assumes the control task, it requires good real-time performance, high reliability and strong adaptability.

Supervisory computer control system

This system performs optimization analysis and calculation according to the working conditions of the production process and the predetermined mathematical model, and generates the optimal settings The value is sent to the direct digital control system for execution. The supervisory computer system is responsible for high-level control and management tasks, requiring strong data processing functions and large storage capacity. Generally, higher-end microcomputers are used.

Hierarchical control system

It is also the DCS system. For details, please see the entry on Distributed Control System.

Fieldbus control system

also known as FCS, is a new generation of distributed control system. This system improves the high cost of the DCS system, and the product communication standards of various manufacturers are not uniform, which results in the weakness of not being able to interconnect.

In recent years, due to the development of fieldbus, smart sensors and actuators have also developed in the direction of digitization, replacing 4-20mA analog signals with digital signals, laying the foundation for the application of fieldbus. Fieldbus is a fully digital, two-way, multi-site serial communication network that connects industrial field instruments and control devices. Fieldbus is called the industrial control network standard of the 21st century.

Development trend

The development of the microcomputer control system is closely linked with the development of the microcomputer, the core part of the control system. Since the rise of microcomputers and microprocessors in the 1970s, the development has been extremely rapid: the integration of chips has become higher and higher; the capacity of semiconductor memory has become larger and larger; control and computer performance have increased by an order of magnitude almost every two years. In addition, a large number of new interfaces and special-purpose chips are constantly emerging, and software is becoming more and more complete and abundant, which greatly expands the functions of microcomputers, which creates conditions for promoting the development of microcomputer systems.

Currently, computer control technology is developing towards intelligence, networking and integration. The development trend of microcomputer control systems is as follows:

· Low-cost industrial control automation based on industrial PCs will become the mainstream.

· PLC is developing in the direction of miniaturization, networking, and PC integration and openness.

· DCS system for integrated design of measurement, control and management.

· The control system is developing in the field bus (FCS) direction.

· Instrumentation technology is developing in the direction of digitization, intelligence, networking, and miniaturization.

· The industrial control network will develop in the direction of the combination of wired and wireless.

· Industrial control software is developing in the direction of advanced control.

Low-cost industrial control automation based on industrial PCs will become the mainstream:

Industrial control automation mainly includes three levels, from bottom to top It is basic automation, process automation and management automation, and its core is basic automation and process automation. In the traditional automation system, the basic automation part is basically monopolized by PLC and DCS, and the process automation and management automation part are mainly composed of minicomputers. Since the 1990s, due to the development of PC-based industrial computers (industrial PCs), PC-based automation systems composed of industrial PCs, I/O devices, monitoring devices, and control networks have been rapidly popularized and become low-achieving An important way to cost industrial automation.

Because PC-based controllers are proven to be as reliable as PLCs and are accepted by operators and maintenance personnel, manufacturers one after another are adopting PC control solutions in at least part of their production. The PC-based control system is easy to install and use, has advanced diagnostic functions, and provides system integrators with more flexible options. From a long-term perspective, PC control systems have low maintenance costs.

Industrial PC mainly includes two types: IPC industrial computer and CompactPCI industrial computer and their deformation machines. Because basic automation and process automation have high requirements on the operational stability, hot swap and redundant configuration of industrial PCs, the existing IPC can no longer fully meet the requirements, and will gradually withdraw from this field, and will be replaced by CompactPCI-based industrial computers. , And IPC will occupy the management automation layer.

When the "soft PLC" appeared, it was thought that industrial PCs would replace PLCs. However, today the industrial PC has not replaced the PLC. There are two main reasons: one is the system integrator; the other is the software operating system. A successful PC-based control system must have two points: one is that all work must be completed by software on a platform; the other is to provide customers with everything they need. The competition between industrial PCs and PLCs will be mainly in high-end applications, with complex data and high equipment integration. Industrial PCs cannot compete with low-cost micro PLCs, which is also the fastest growing part of the PLC market. From the perspective of development trends, the future of control systems is likely to exist between industrial PCs and PLCs.

PLC is developing towards miniaturization, networking, PCization and openness:

For a long time, PLC has always been the main battlefield in the field of industrial control automation. The automation control equipment of the company provides a very reliable control scheme, forming a tripartite trend with DCS and industrial PC. At the same time, PLC also bears the impact from other technical products, especially the impact brought by industrial PCs.

Miniaturization, networking, PCization and openness are the main directions for the future development of PLC. In the early days of PLC-based automation, PLCs were large and expensive. But in recent years, micro PLC has appeared, the price is only a few hundred yuan. With the further improvement and development of soft PLC control configuration software, the market share installed with soft PLC configuration software and PC-based control will gradually increase.

Currently, one of the biggest development trends in the field of process control is the expansion of Ethernet technology, and PLC is no exception. More and more PLC suppliers begin to provide Ethernet interface. It is believed that PLC will continue to shift to the direction of open control systems, especially control systems based on industrial PCs.

DCS system for integrated design of measurement, control and management:

Miniaturization, diversification, PCization and openness are the main directions of future DCS development. The market occupied by small DCS has been gradually shared with PLC, industrial PC, and FCS. In the future, small-scale DCS may be the first to integrate with these three systems, and "soft DCS" technology will first be developed in small-scale DCS. PC-based control will be more widely used in small and medium-scale process control, and various DCS manufacturers will also launch small-scale DCS systems based on industrial PCs. The open DCS system will extend both upwards and downwards at the same time, allowing on-site data from the production process to flow freely within the entire enterprise, realizing the seamless connection of information technology and control technology, and developing towards the integration of measurement, control and management.

The control system is developing in the field bus (FCS) direction:

Due to the development of 3C technology, the process control system will develop from DCS to FCS. FCS can completely decentralize PID control to field devices. Fieldbus-based FCS is a new generation of production process automation system that is fully decentralized, fully digital, fully open and interoperable. It will replace the one-to-one 4-20mA analog signal line in the field and give the traditional industrial automation control system. The structure brings revolutionary changes.

According to the definition of IEC61158, fieldbus is a digital, two-way transmission, multi-branch structure communication network between field devices installed in the manufacturing or process area and automatic control devices in the control room. The field bus enables the measurement and control equipment to have digital calculation and digital communication capabilities, improves the accuracy of signal measurement, transmission and control, and improves the function and performance of the system and equipment. In addition to the eight field buses of IEC61158, IEC TC17B has passed three bus standards: SDS, ASI, and Device NET. In addition, ISO published the ISO 11898 CAN standard. In the competition of various fieldbuses, the COTS communication technology represented by Ethernet is becoming a new bright spot in the fieldbus development. The use of fieldbus technology to construct a low-cost fieldbus control system, promotes the intelligentization of field instruments, the decentralization of control functions, and the openness of the control system, in line with the technological development trend of industrial control systems. In a word, the development of computer control system will move towards field bus control system (FCS) after experiencing base pneumatic instrument control system, electric unit combined analog instrument control system, centralized digital control system and distributed control system (DCS). The direction of development. Although FCS based on fieldbus has developed rapidly, there is still a lot of work to be done in the development of FCS, such as unified standards and intelligent instrumentation. In addition, the maintenance and transformation of traditional control systems also require DCS. Therefore, it will take a long time for FCS to completely replace traditional DCS. At the same time, DCS itself is constantly developing and improving. To be sure, FCS combined with new technologies such as DCS, industrial Ethernet, and advanced control will have strong vitality. Industrial Ethernet and fieldbus technology, as a flexible, convenient and reliable data transmission method, have been more and more used in the industrial field, and will occupy a more important position in the control field.

The combination of computer network technology, wireless technology and smart sensor technology has produced a new concept of "networked smart sensor based on wireless technology". This kind of networked smart sensor based on wireless technology enables industrial field data to be transmitted, published and shared directly on the network through wireless links. Wireless local area network technology can provide high-bandwidth wireless data links and flexible network topology for communication between various intelligent field devices, mobile robots and various automation equipment in a factory environment, effectively making up for it in some special environments To overcome the shortcomings of the wired network, the communication performance of the industrial control network is further improved.

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