Stepper motors can achieve open-loop control of position and speed based on the number and frequency of pulses, making them an inexpensive, simple, and user-friendly control type of motor. They are increasingly widely used in the field of automation control. However, due to the fact that the stepper motor is not a closed-loop control, improper selection or use can also easily lead to stepper motor loss of step, also known as stepper motor loss of step, which means that the stepper motor does not reach the desired position according to instructions, causing engineers great distress. So, what is the reason for the stepper motor losing step? What measures can be taken to avoid losing step?
There are many reasons for stepper motor stepping out, and in practical applications, it is necessary to adopt an elimination method to analyze one by one in order to identify the true cause of stepping out. Generally, the reasons for stepping out are as follows:
1. The working torque of the stepper motor itself is not sufficient, and it does not have sufficient capacity to drive the load;
2. The acceleration and deceleration process of the stepper motor is insufficient, and the stepper motor loses step during the acceleration and deceleration process;
3. Insufficient power supply of the stepper motor leads to insufficient input power of the stepper motor, resulting in loss of step;
4. The driving voltage of the stepper motor is insufficient or the driving current is set too low;
5. The driver or controller receives signal interference;
6. The resonance of the stepper motor system causes a decrease in the load-bearing capacity of the stepper motor, resulting in a loss of step;
7. The signals of the driver and controller do not match;
8. The back clearance or back and forth clearance error of the synchronous wheel or gearbox has not been compensated in the program or the compensation value is incorrect;
9. There is an issue with the control program itself.
In response to the causes of the above problems, the following measures can be taken to improve the problem of stepping motor out of step:
1) Calculate the torque of the load and refer to the stepper motor frequency diagram to see if the stepper motor has sufficient torque capacity to drive the load at the corresponding speed. You can compare and test it with a stepper motor with higher torque at the corresponding working speed.
2) The starting stage of a stepper motor is like driving a car with manual waves, requiring gradual upshifting and acceleration. Insufficient acceleration and deceleration can lead to loss of step. It is generally recommended that the rotational inertia of the load should not be greater than 10 times the rotational inertia of the stepper motor, otherwise the acceleration and deceleration process will be relatively long.
3) At the moment of starting the stepper motor, we will test a current of about 1.6 times the rated current. If the power supply is insufficient, the effective current inside the motor will be too low, making it unable to carry the load. It is recommended to leave more than 30% margin for general power supply.
4) The stepper motor needs to start quickly or run at high speed, requiring a relatively high driving voltage and a sufficiently large set working current, otherwise it is also prone to stepping out.
5) Compare with a different model of driver to see if there is signal interference, or check if motor A is controlling the movement of motor B, and see if motor B is receiving signal interference.
6) When resonance occurs, there is significant noise and vibration in the stepper motor and its system. When the speed increases or decreases within a certain range, the related phenomena will be significantly reduced or disappear, and it can be basically judged that it is a resonance problem. Choose a stepper motor with appropriate parameters to improve driver performance or use physical methods such as shock absorbers to reduce vibration.
7) If the signals of the stepper motor driver and controller do not match, the phenomenon is that the displacement of the position will increase uniformly over time. Just change the signal recognition method of the driver or controller to match them consistently.
8) Due to accuracy issues, there may be accumulated errors in the synchronous wheel or gearbox, and reasonable compensation needs to be made in the control program.
9) It is not uncommon for the control program to cause stepping out, and it is necessary to check if there is a problem with the control program.
Using closed-loop control to achieve complete control of stepper motors is also a solution to the problem, but the cost will be higher. Nowadays, some stepper motor drive chips can output signals of stepper motor out of step based on abnormal changes in the instantaneous current of the stepper motor out of step.
Source: Mechanical Transmission