Open loop control and closed loop control

Firstly, the concepts of control system and control theory are briefly introduced.

Academically speaking, the control system is a device that can change the future state of the system. It is independent of the controlled object itself and is a device designed by us to give control signals to the controlled object. The control theory is the method and strategy to help us design this device reasonably.

In plain English, there is a system. Give it an Input and it will have an output. Now we want it to output as we want. At this point, the control system is what produces input, and the control theory tells us what input to give.

Open-loop control refers to the control mode that the input does not depend on the output; The closed-loop control means that the output will be fed back to the input end, thus affecting the control mode of the input.

Give an example of a dishwasher. In the figure below, when we only input the control variable of time, it is open-loop control, because once the control variable time is set, it will not change, and it will not change with the change of output-plate cleanliness;

When we install a detector on the output side to form feedback, it constitutes a closed-loop control. In the process of closed-loop control, a reference value will be set first, here is the cleanliness of the plate; The detection result will be fed back to the input end of the controller and compared with the reference value we set to get the error e; The controller gets the input result according to E. If E>0, it means that the dish has not been cleaned, and the cleaning time t needs to be increased until E=0, and the dish is cleaned. This process of constant feedback and correction of input constitutes a complete closed loop, that is, "closed loop control".

At this point, we can see the benefits of closed-loop system:

It has the ability of adaptive adjustment, which can automatically adjust the input signal, so that the system can output the reference value we want, and this process does not need human intervention;

The stability is higher, and the adaptive ability improves the stability of the system, because it can "correct" unreasonable input and prevent the system from crashing caused by unreasonable input;