Calculation Skills for Positioning Accuracy of Stepper Motors

Because the open-loop control system has the advantages of convenient operation and low price, the basic stepping motor is mainly used in open-loop control. Although stepper motors are widely used, they cannot be used under normal conditions like ordinary AC direct current motors, and the running speed from the start point to the end point is under theoretical conditions, when the limit starting frequency of the motor is greater than the running speed. The motor can be operated as required and can reach the expected operating speed.

At the end of the stroke, the pulse that can achieve the stop function can be immediately issued and the motor can be stopped. However, the actual situation is that the stepper motor can achieve a lower limit start pre-rate, which is far from meeting the requirements of higher running speed. Under this working condition, if the motor is forced to start directly at the required speed (greater than the limit starting pre-rate), "lost step" or no response will occur. When the motor runs to the end point, although the pulse has been stopped immediately to stop it, due to the inertia, the phenomenon of overshooting occurs, that is, overshoot occurs.

It is particularly noteworthy that in order to ensure the positioning accuracy of the system (the speed of the motor is slow and slow, to prevent "out of step" or "overshoot") and to obtain high positioning speed, the mainstream system divides the positioning process into coarse The positioning phase and the fine positioning phase are performed. According to the production practice experience, “lost step” and “overshoot” are the two “criminals” that occur most frequently in the operation of stepper motors, which seriously affect the positioning accuracy of stepper motors.

The main reasons for the inaccurate positioning include:

(1) The initial starting speed is required to be too high, exceeding the limit starting frequency of the motor, or the acceleration is too large, resulting in “lost steps;

(2) The power of the motor motor does not meet the requirements of the system;

(3) The working process of the actuator is subject to interference;

(4) The controller of the control system generates a malfunction;

(5) When the commutation, the pulse is lost, the one-way operation is accurate, the deviation occurs after the commutation, and the deviation spring is more obvious although the number of commutation times increases;

(6) Software has design flaws;

(7) In the case of using the timing belt, the software compensates too much or too little.