What is the Difference between an Open-loop Stepper Motor and a Closed-loop Stepper Motor?

Open loop and closed loop are terms often used in control systems. Open-loop stepper motors and closed-loop stepper motors are also distinguished and named according to their control systems. Therefore, to understand the difference between them, we must first understand the difference between open loop control and closed loop control, and their differences are as follows:

1. Different working principles

The open-loop control system can neither detect nor correct errors. The control accuracy and the performance of suppressing interference are relatively poor, and it is very sensitive to the change of system parameters. Therefore, it is generally only used in some occasions where external influences can be ignored, or inertia is small, or precision 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 the correction action more accurate and more powerful. But it lacks the preventative qualities of open-loop control. Corrective action should be taken only if adverse consequences are caused in the control process. Therefore, it is generally widely used in situations with high requirements and high precision for the external environment.

2, The structure is different

The open-loop system has no testing equipment and is simple in composition, but the selected components must strictly ensure the 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. Different stability

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

How to determine open loop and closed loop system?

The judgment of the open-loop closed-loop system is whether there is feedback and whether it plays a role in the current control. Open-loop control is generally a control activity that is completed in an instant, and closed-loop control must last for a certain time, which can be used to judge the feed link.

Open loop control refers to the control process in which there is only a forward action and no reverse connection between the control device and the controlled object. Therefore, the output of the open-loop control system does not affect the control function of the system. Such as vending machines, automatic washing machines, automatic product production lines, automatic lathes, etc., are generally open loop control systems.

Closed-loop control system: Closed-loop control is a control mode that corrects according to the output feedback of the control object, and corrects according to the norm or standard when the deviation from the actual plan is measured. Closed-loop control, take out the control signal from the output change as a comparison feedback to the input control input, generally this take out and the input phase is opposite, so it is called negative feedback control.

From the above information, we can conclude that the fundamental difference between the open-loop stepper motor and the closed-loop stepper motor is that the motor will not feedback the current state of operation. The open-loop stepper motor has no feedback signal, only performs the action in sequence, and does not detect the output result, and does not correct the output.

On the contrary, the closed-loop stepper motor has a feedback signal, which takes the corresponding action measures or signals according to the stepper motor driver to feed back to the PLC, and the PLC decides the next step of the program processing. That is to say, the closed-loop stepper motor detects the output result and corrects it according to the difference between the output result and the theoretical requirements. Therefore, the precision of the closed loop is higher than that of the open loop.

Other differences between open-loop stepper motors and closed-loop stepper motors

1, the closed-loop stepper motor increases the encoder, while the closed-loop driver and closed-loop stepper motor need to be used in complete sets;

2, fast response: the closed-loop stepper motor has very good instantaneous synchronization, so the closed-loop stepper motor has more advantages for short distance accurate and fast positioning applications.

3, the closed-loop stepper motor can adjust the winding current according to the load, thereby reducing the temperature rise of the motor and improving the efficiency of the system;

4, closed-loop stepper motor can give a certain overload current in a short time to help overcome the instantaneous load lag;

5, closed-loop stepper motor in the selection of motor load torque can consider small or even do not leave a margin, and open-loop stepper motor generally to retain 30% of the torque margin to prevent gridlock;

6. The acceleration of the open-loop stepper motor is too fast and the load is stuck at an instantaneous speed, which may cause the load to exceed the torque of the motor at the current speed, and the closed-loop stepper motor can reduce the requirements on the acceleration and deceleration curve of the upper control to prevent out-of-step gridlock.

Article source: https://article-realm.com/article/Product-Reviews/48298-What-is-the-Difference-between-an-Open-loop-Stepper-Motor-and-a-Closed-loop-Stepper-Motor.html