Historical development of automatic control

The earliest automatic control can be traced back to the ancient automatic timer and leaky pot compass in China, and the wide application of automatic control technology began in the industrial revolution in Europe. The Englishman Watt invented the centrifugal governor in 1788 by applying the feedback principle while inventing the steam engine. When the load or steam supply changes, the centrifugal governor can automatically adjust the opening of the intake valve, thus controlling the speed of the steam engine.

150 years ago, the first generation process control system was based on 5- 13 psi pneumatic signal standard (PCS). Simple local operation mode, control theory is initially formed, and there is no concept of control room.

The second generation process control system (analog control system or ACS) is based on the current analog signal 0- 10MA or 4-20MA. This obvious progress has firmly ruled the whole field of automatic control for 25 years. It marks the arrival of the era of electrical automatic control. The control theory has made great progress, and the establishment of three cybernetics has laid the foundation of modern control; The establishment of the control room and the separation of control functions have been used to this day.

The Third Generation Process Control System (CCS). The application of digital computers began in the 1970s, which produced great technical advantages. People are ahead in the fields of measurement, simulation and logic control, thus the third generation process control system (CCS) is produced. This proces control system, called that third generation, is a revolution in the field of automatic control, which give full play to the specialty of computers, so it is generally believed that computers can do everything well, and naturally a central control compute system called "centralized control" appears. It should be pointed out that the signal transmission system of this system still mostly uses 4-20 mA analog signals, but it is not long before people find that with the problems of centralized control and reliability, the danger of losing control is also concentrated, and a little carelessness will paralyze the whole system. So it quickly developed into a distributed control system (DCS).

The fourth generation process control system (DCS): With the rapid development of semiconductor manufacturing technology and the wide use of microprocessors, the reliability of computer technology has been greatly improved. At present, the fourth generation process control system (DCS) is widely used. Its main feature is that the whole control system is no longer just a computer, but a control system composed of multiple computers and some intelligent instruments and components. So decentralized control has become the most important feature. In addition, another important development is that the signal transmission between them not only depends on the 4-20 mA analog signal, but gradually replaces the analog signal with digital signal.

The fifth generation process control system (FCS): FCS is developed from DCS, just as DCS is developed from CCS, which is a qualitative leap. "Decentralized control" developed to "field control"; Data transmission adopts "bus" mode. But the real difference between FCS and DCS is that FCS has a broader development space. Although the technical level of the traditional DCS is constantly improving, the lowest end of the communication network only reaches the level of the field control station. The connection between the field control station and the field detection instruments and actuators still uses 4-20mA analog signals for one-to-one transmission, which is costly, inefficient and difficult to maintain.

Comprehensive monitoring and in-depth management of the working state of field equipment. The so-called field bus is the intelligent test of connection.

All-digital, bidirectional transmission capacity and control equipment, communication link adopts multi-node branch structure. simple

Simply put, traditional control is a loop, while FCS technology is that all modules such as controller, actuator and detector are hung on a bus to realize communication and of course transmit digital signals. Main total

There are Profibus, LonWorks and so on.

1, 1940s-early 1960s:

Demand power: market competition, resource utilization, reducing labor intensity, improving product quality and meeting the needs of mass production. Main features: This stage is mainly a single-machine automation stage. The main features are: the emergence of various single-machine automation processing equipment, and the continuous expansion and in-depth development of applications. Typical achievements and products: CNC machine tools with hardware CNC system.

2. From the mid 1960s to the early 1970s:

Demand power: The intensified market competition requires fast product update and high quality, which can meet the needs of large and medium-sized mass production and reduce labor intensity. Main features: This stage is mainly marked by automated production lines. Its main features are: on the basis of single machine automation, various combined machine tools and combined production lines appear, at the same time, software numerical control systems appear and are used in machine tools, and CAD, CAM and other software are used in the design and manufacture of practical projects. At present, hardware processing equipment is suitable for large and medium-sized production and processing. Typical achievements and products: automatic production line for drilling, boring and milling.

3. Mid-1970s-up to now: Demand power: The change of market environment makes the universality problem in multi-variety, small and medium-sized batch production more and more serious, which requires the automation technology to develop in breadth and depth, make its related technologies highly integrated and give full play to the overall best efficiency. Main features: Since American scholars first put forward the concept of CIM in the early 1970s, great changes have taken place in the field of automation. Its main features are: CIM, as a philosophy and method, has been gradually accepted; CIM is also the corresponding technology to realize integration, which integrates decentralized and independent unit automation technology into an optimized whole. The so-called philosophy is that enterprises should analyze and overcome the existing "bottlenecks" according to their own needs, so as to realize the ideological strategy of continuously improving their own strength and competitiveness; As the corresponding technology to realize integration, it is generally considered as: data collection, distribution and * * * sharing; Network and communication; Workshop equipment controller; Specifications and standards of computer hardware and software, etc. At the same time, concurrent engineering, as a management concept and working mode, has been applied and active in the field of automation technology since the late 1980s, and will further promote the integration of unit automation technology. Typical achievements and products: CIMS factory, flexible manufacturing system (FMS).

With the introduction of new achievements in modern applied mathematics and the application of electronic computers, in order to adapt to the development of aerospace technology, automatic control theory has entered a new stage-modern control theory. This paper mainly studies the optimal control of multivariable parameters with high performance and high precision, and the main method is the state space method based on state. At present, the automatic control theory is still developing, and it is going deep into the intelligent control theory based on cybernetics, information theory and bionics.

In order to realize all kinds of complex control tasks, the controlled object and the control device must be connected in a certain way to form an organic whole, which is the automatic control system. In the automatic control system, the output of the controlled object, that is, the controlled quantity, is a physical quantity that needs strict control and can be kept at a constant value, such as temperature, pressure or flight trajectory. The control device is the sum of the mechanisms that control the controlled object. It can control the controlled object in different principles and ways, but the most basic one is the feedback control system based on the feedback control principle.

In the feedback control system, the control function of the control device on the controlled device is the feedback information from the controlled quantity, which is used to constantly correct the deviation between the controlled quantity and the controlled quantity, so as to realize the task of controlling the controlled quantity. This is the principle of feedback control.