What does open loop and closed loop mean?

introduction

In embedded development , We often encounter a concept of control field , Open loop and closed loop . Even if you are not a control professional , If you want to engage in embedded , I suggest you also need to understand the concepts of open-loop and closed-loop . Open loop and closed loop are terms often used in control . Open loop control refers to the control process in which there is only forward action between the control device and the controlled object, but no reverse connection , The system formed in this way is called open loop control system . Closed loop control is to feedback the output directly or indirectly to the input to form a closed loop 、 Control mode of participation control .

Introduce

Open loop

The English name of open loop is open-loop. Open loop versus closed loop , Also called open loop control system . It means that the control results will not be fed back to affect the current control system . Open loop is equivalent to one-way operation , We give the controller a value , The controller operates and controls according to this value . That is, only control the output , Reckless control . This system is relatively simple , Easy to use , Stable work , But the improvement of accuracy and speed is limited , Therefore, it is generally only used without considering external influences , Or small inertia 、 Some systems with low accuracy requirements . For example , Open loop is equivalent to boiling water faucet , Where do you screw it , The faucet can produce as much water , No feedback signal .

closed loop

Closed loop is also called feedback control system , It is an automatic control system with a closed loop composed of signal forward path and feedback path , It is to compare the measured value of the system output with the expected given value , This produces a deviation signal , Use this deviation signal for adjustment control , Make the output as close to the expected value as possible . Closed loop control , People usually set goals , The feedback detection data is implemented by the circuit's own detection circuit . The operation process of reaching the tracking setting is called closed-loop control . Closed loop means that the controlled output returns to the control input in a certain way , A control relationship that exerts control influence on the input . Open loop control without feedback , Will firmly execute the instructions of the operator , The closed-loop control may terminate the command due to some problems .
In other words , Open loop control as long as the command is issued , It will be in place in one step , And after the closed-loop control command goes down , The operator will receive a feedback message , It may refer to the instruction because of the feedback message .
The specific content refers to ： Part or all of the output of the control system , It is sent back to the input end of the system through certain methods and devices , Then compare the feedback information with the original input information , Then apply the comparison results to the system for control , Avoid the system from deviating from the predetermined goal . The closed-loop control system utilizes negative feedback . That is, an automatic control system with a closed loop composed of a positive signal path and a feedback path , Also known as feedback control system .
Closed loop to Take a water dispenser or a more advanced electric kettle as an example , It doesn't matter to you , The water is boiling , Automatic power-off insulation . Water cooled , Power on automatically , Heat up .
This system has high positioning accuracy , But the system is complex 、 Difficult commissioning and maintenance , The price is more expensive , It is mainly used in high-precision systems .

The difference between open loop and closed loop

1. It works differently
   The open-loop control system cannot detect errors , Nor can the error be corrected . The control accuracy and interference suppression performance are relatively poor , And it is very sensitive to the change of system parameters . therefore , Generally, it is only used without considering external influence , Or small inertia , Or some occasions with low accuracy requirements .
   The advantage of closed-loop control is to give full play to the important role of feedback , Eliminate unpredictable or uncertain factors , Make the correction action more accurate , More powerful . But it lacks the preventive effect of open-loop control . Take corrective measures only when adverse consequences are caused in the control process . therefore , Generally, it is widely used with high requirements for the external environment 、 High precision occasions .
2. The structure is different
   The open-loop system has no detection equipment , The composition is simple , However, the selected components should strictly ensure the quality requirements . The closed-loop system has the ability to suppress interference , Insensitive to changes in component characteristics , And can improve the response characteristics of the system .
3. The stability is different
   The stability of open-loop control system is relatively easy to solve . The introduction of feedback loop in closed-loop system increases the complexity of the system .

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