What are the composition and characteristics of open-loop, closed-loop and semi-closed-loop control systems?

What are the composition and characteristics of open-loop, closed-loop and semi-closed-loop control systems? The CNC machine tool with open-loop control system has no position detection device, and only works according to the command pulse of the CNC device, without detecting and feeding back the actual displacement of the moving parts. Usually, the power stepping motor is used as the actuator.

The system has simple structure, convenient debugging, low price and easy maintenance, but its accuracy is low. Therefore, it is mostly used for economical CNC machine tools.

The CNC machine tool with closed-loop control system is equipped with a position detection device on the moving parts of the machine tool, which can feed back the measured displacement to the comparator of the CNC device at any time, compare it with the input instruction, and control the moving parts with the difference value to make the moving parts move strictly according to the actual displacement.

The system has high machining precision and fast moving speed. However, the installation and debugging are more complicated, and the cost of the position detection device is higher, so it is mostly used in high-precision CNC machine tools and large CNC machine tools.

The CNC machine tool of semi-closed-loop control system is to install position detection elements at the end of the drive motor or drive screw, and indirectly detect the displacement (or angular displacement) of the moving parts by detecting the rotation angle of the servo motor, and feed it back to the comparator of the CNC device, compare it with the input instructions, and control the moving parts with the difference.

The system has simple measuring device, convenient installation and debugging, and good system stability. It can obtain higher accuracy than open-loop control system, but its displacement accuracy is lower than closed-loop control system, so it is mostly used in mid-range CNC machine tools.

Briefly describe the characteristics of open-loop and closed-loop control systems. The characteristics of open-loop and closed-loop control systems can be mainly analyzed from three aspects.

1. working principle: the open-loop control system can neither detect errors nor correct them. The control accuracy and interference suppression efficiency are poor, and it is sensitive to the change of system parameters. Whatever the reason (external disturbance or internal change of the system), as long as the controlled quantity deviates from the specified value, the corresponding control function will be generated to eliminate the deviation. The control accuracy and interference suppression efficiency are poor, and it is sensitive to the change of system parameters. Therefore, it is generally only used in some occasions where the external influence can be ignored, or the inertia is small, or the accuracy requirement is not high.

2. Structure composition: The open-loop system has no detection device and simple composition, but the selected components must strictly meet the quality requirements. The closed-loop system has the ability to suppress interference, is insensitive to the change of component characteristics, and can improve the response characteristics of the system.

3. Stability: The stability of the open-loop control system is relatively easy to solve. The introduction of feedback loop in closed-loop system increases the complexity of the system.

What are open-loop and closed-loop control systems? The feedback control system is called closed-loop control system. A control system without feedback is called an open-loop control system. For example, the heating control system is an open-loop control system regardless of temperature. If the heating control system can control the heating power or heating time through temperature feedback, then the heating control system is called a closed-loop control system.

The servo control technology of the developed closed-loop stepping motor driver is superior to the traditional and current domestic mainstream hybrid servo. SS series closed-loop stepping can be automatically adjusted, and the load current can be automatically adjusted. Under the condition of low load, the automatic adjustment and rapid reduction of current can reduce the noise and heat of the motor. Suddenly, when the load current is quickly adjusted in real time, it can maintain high-precision position control and high-speed operation without interruption.

Closed-loop control is a basic concept of cybernetics. Refers to a control relationship in which the controlled output returns to the controlled input in some way and exerts control influence on the input. For example, an automatic washing machine has an infrared sensor in it to scan the water level when adding water to the washing machine. When the water level is suitable, the washing machine automatically stops adding water.

Open-loop control does not need to take the output change signal to deduct the salary input. Manual control is generally open-loop control, for example, speed control is achieved by manually changing the gear of electric fan, and the actual speed is not fed back.

A control system with feedback is called a closed-loop control system. A control system without feedback is called an open-loop control system. For example, a heating control system, you don't care about the temperature, just heat it. This is an open-loop control system. If a heating control system can control heating power or heating time through temperature feedback, this heating control system is called closed-loop control system. Open-loop control system: a system that does not feed back the control results and affects the current control. For example, turn on the switch of the light-the control activity has ended at the moment after pressing the switch, and whether the light is on or not has no effect on the activity of pressing the switch; Shooting-after basketball is shot, it can't be controlled anymore. Whether the ball scores or not, the control of the ball is over in an instant. Closed-loop control system: a system that can feed back the control result and compare it with the expected value, and adjust the control function according to its error. For example, adjust the faucet-first have an expected flow rate in your mind, after the faucet is turned on, observe the existing flow rate with your eyes and compare it with the expected value, and constantly adjust it by hand to form a feedback closed-loop control; Cycling-Similarly, the direction and speed of travel are constantly revised to form the difference between closed-loop control and open-loop closed-loop: 1, with or without feedback; 2. Whether it is applicable to the current control. Open-loop control is generally an instantaneous control activity. Closed-loop control will certainly last for some time. It can be judged that the first shot of the lens is closer to the second shot, which is also a kind of feedback but will not affect the first shot. Therefore, it is a manual control system with open-loop control: a system automatic control system that can only complete the control task under the direct intervention of human beings: a control system that can be executed according to the expected law or predetermined procedure without human intervention: a bicycle-manual closed-loop system, a missile-automatic closed-loop system, a manned-manual open-loop system, an automatic door, an automatic street lamp-automatic open-loop system; The closed-loop control of engine EFI system is real-time oxygen sensor, computer and fuel. The oxygen sensor "tells" the air-fuel ratio of the mixed gas to the computer, and the computer sends an instruction to the oil quantity control device to adjust the air-fuel ratio to the theoretical value (14.7: 1). This adjustment often exceeds the theoretical value, and the oxygen sensor will detect it and report it to the computer, which will then issue a command to adjust it back to 14.7: 1. Because each adjustment cycle is fast, the air-fuel ratio will not deviate from 14.7: 1. Once implemented, this closed-loop adjustment will continue. The closed-loop control EFI engine can always work under ideal working conditions (the air-fuel ratio will not deviate too much from the theoretical value), thus ensuring that the car not only has good power efficiency, but also saves fuel. Closed-loop control, the control signal is taken from the output change as the comparison quantity and fed back to the input terminal to control the input quantity. Generally, the output is opposite to the input, so it is called negative feedback control, and automatic control is usually closed-loop control. Closed-loop control is a basic concept of cybernetics. Refers to a control relationship in which the controlled output returns to the controlled input in some way and exerts control influence on the input. In cybernetics, closed loop usually means that the output end feeds back to the input end through "side chain", which is called closed loop control. The output end feeds back to the input end and participates in the re-control of the output end. This is the purpose of closed-loop control, which is achieved through feedback. Positive feedback and negative feedback are two common basic forms of closed-loop control. Among them, from the perspective of achieving the goal, negative feedback and positive feedback have the same meaning. From the specific way of feedback realization, both positive feedback and negative feedback belong to the "addition and subtraction" feedback mode in algebraic or arithmetic sense, that is, after the output is fed back to the input, it is integrated with the input, and then used as a new control output to further control the output. In fact, the feedback from output to input is far more than these ways. This is manifested in: in operation, it includes not only addition and subtraction, but also a wider range of mathematical operations; In the feedback mode, the output does not necessarily need to be integrated with the input to form a unified control output, and the output can be directly controlled by the control chain. Closed-loop control has specific performance in various control examples, such as the above-mentioned automobile engine combustion control.

Semi-closed-loop control system defines that open-loop control has no feedback link, so the stability of the system is not high, the response time is long and the accuracy is not high. It is used in simple systems that do not require high stability and accuracy.

Open-loop control refers to the control process in which the control device and the controlled object only work in sequence without reverse connection. The system formed in this way is called an open-loop control system, and its characteristic is that the output of the system will not affect the control function of the system, and it has no ability of automatic correction or compensation.

Closed-loop control has a feedback link. Through the feedback system, the accuracy of the system is improved and the response time is shortened, which is suitable for systems with high requirements on response time and stability.

The semi-closed-loop control system is to install an angular displacement detection device in the servo mechanism of the open-loop control system, indirectly detect the displacement of the moving parts by detecting the angle of the ball screw of the servo mechanism, and then feed it back to the comparator of the numerical control device, compare it with the input original command displacement value, and control it with the compared difference value, so that the moving parts can supplement the displacement until the difference value is eliminated. This servo mechanism is superior to the open-loop servo mechanism in accuracy, speed and dynamic characteristics, and is adopted by most small and medium-sized CNC machine tools.

What is the difference between closed-loop control system and semi-closed-loop control system in CNC machine tools? Full closed loop corresponds to half closed loop. The semi-closed-loop CNC machine tool feeds back the walking state of the machine tool through the encoder built in the servo motor. Semi-closed-loop CNC machine tool can't truly reflect the walking state of the machine tool because of the error in the transmission link, and the accuracy of the machine tool is slightly lower. /Full-closed-loop CNC machine tool uses grating ruler to feed back the moving parts of the machine tool in real time, and informs the servo motor of the machine tool state after being processed by the CNC system. Servo motor automatically compensates motion error through system instruction. Because the grating ruler reflects the real walking state of the moving parts and reduces the motion error of the machine tool through compensation, the precision of the fully closed-loop CNC machine tool is relatively high.

How to distinguish open-loop and closed-loop control system audit evaluation: the content is more substantial

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Control system is one of the key and difficult points in general technology course. Throughout the two general technology college entrance examinations, this knowledge point occupies a considerable weight. However, this is more professional knowledge. Without this knowledge, teachers may encounter many problems, especially the distinction between open-loop and closed-loop control systems. If we want to distinguish easily, we must grasp a key and make clear two basic points.

Keywords: control system, open-loop control system, feedback of closed-loop control system

Control and design is one of the difficulties of general technology. In teaching, teachers should be familiar with the professional knowledge about automatic control and understand the basic theory and working principle of control system, especially the difference between open-loop and closed-loop control systems, which often puzzles many general technical teachers. In the general technical college entrance examination syllabus, the requirements are relatively high, and the exact meaning of the listed knowledge should be understood.