Open loop, closed loop

JackIeLc

Open loop, closed loop [Copy link]

In embedded development, you often encounter a concept in the field of control, that is, open loop and closed loop. Even if you are not a control major, if you want to work in embedded, I suggest that you also need to understand the concept of open loop and closed loop. Open loop and closed loop are terms often used in control. Open loop control refers to a control process in which there is only a forward action but no reverse connection between the control device and the controlled object. The system formed in this way is called an open loop control system. Closed loop control is a control method in which the output quantity is directly or indirectly fed back to the input end to form a closed loop and participate in control.

introduce

Open Loop

The English name of open loop is open-loop. Open loop is relative to closed loop, and is also called open-loop control system. It means that the control result is not fed back to affect the current control system. Open loop is equivalent to one-way operation. We give the controller a value, and the controller operates and controls according to this value. That is, it only controls the output without considering the consequences. This system is relatively simple, easy to master and use, and works stably, but the improvement of accuracy and speed is limited, so it is generally only used for some systems that do not consider external influences, or have small inertia and low accuracy requirements. For example, open loop is equivalent to turning on the faucet. The faucet will output as much water as you turn it to, and there is no feedback signal.

closed loop

Closed loop, also called feedback control system, is an automatic control system consisting of a closed loop of a signal forward path and a feedback path. It compares the measured value of the system output with the expected given value, thereby generating a deviation signal, which is used to adjust and control the output value to make it as close to the expected value as possible. Closed loop control is generally set by people, and the circuit's own detection circuit implements feedback detection data. The operation process of tracking the setting is called closed loop control. Closed loop refers to a control relationship in which the output as the controlled output returns to the input end as the control in a certain way and exerts a control influence on the input end. Open loop control without feedback will firmly execute the operator's instructions, while closed loop control may terminate the instructions due to some problems.
In other words, as long as the open loop control is issued, it will be in place in one step, and after the closed loop control instruction is issued, the operator will receive a feedback message, and may interrupt the instruction because of the feedback message.
The specific content refers to: part or all of the output of the control system is sent back to the input end of the system through certain methods and devices, and then the feedback information is compared with the original input information, and then the comparison result is applied to the system for control to prevent the system from deviating from the predetermined target. The closed-loop control system uses negative feedback. That is, it is an automatic control system that consists of a closed loop consisting of a signal forward path and a feedback path, also known as a feedback control system.
Take a water dispenser or a more advanced electric kettle as an example. You don't have to worry about it. When the water boils, it automatically turns off the power to keep warm. When the water cools, it automatically turns on the power to heat it.
This system has high positioning accuracy, but the system is complex, difficult to debug and maintain, and expensive. It is mainly used for high-precision systems.

The difference between open loop and closed loop

1. Different working principles:
   Open-loop control systems cannot detect or correct errors. The control accuracy and interference suppression performance are relatively poor, and they are very sensitive to changes in system parameters. Therefore, they are generally only used in some occasions where external influences can be ignored, or where inertia is small, or where accuracy requirements are not high.
   The advantage of closed-loop control is that it gives full play to the important role of feedback, eliminates unpredictable or uncertain factors, and makes correction actions more accurate and powerful. However, it lacks the preventive nature of open-loop control. For example, corrective measures are taken only when adverse consequences are caused during the control process. Therefore, it is generally widely used in occasions with relatively high requirements for the external environment and high accuracy.
2. Different structural compositions:
   The open-loop system has no detection equipment and is simple in composition, but the selected components must strictly meet quality requirements. The closed-loop system has the ability to suppress interference, is insensitive to changes in component characteristics, and can improve the response characteristics of the system.
3. Stability is different.
   The stability of open-loop control systems is relatively easy to solve. The introduction of feedback loops in closed-loop systems increases the complexity of the system.

Jacktang

Open loop is like turning on a faucet. The faucet will produce as much water as you turn it to, and there is no feedback signal.

JackIeLc

Jacktang posted on 2024-11-9 09:39 Open loop is like turning on a faucet. The faucet will produce as much water as you turn it to. There is no feedback signal. This analogy is good

This is relatively easier to understand. I used this method to distinguish them when I was confused at first.