Because open-loop control systems are convenient to operate and inexpensive, my country primarily uses open-loop control reactive stepper motors. Although stepper motors are widely used, they cannot be used under normal conditions like ordinary AC (DC) motors. Theoretically, under conditions where the motor's maximum starting frequency is greater than its operating speed, the motor can run as required and reach the expected speed. It can also immediately send a stop pulse at the end of its stroke to stop the motor. However, in reality, the maximum starting frequency achievable by a stepper motor is relatively low, far from meeting the requirements of higher operating speeds. Under these conditions, forcing the motor to start directly at the required speed (greater than the maximum starting frequency) will result in "step loss" or no response. Furthermore, when the motor reaches its end point, although it immediately stops sending pulses to stop, due to inertia, it may overshoot the end point, resulting in overshoot.
It is particularly noteworthy that, in order to ensure both the positioning accuracy of the system (by slowing down the motor's acceleration and deceleration to prevent "step loss" or "overshoot") and to achieve a high positioning speed, mainstream systems divide the positioning process into a coarse positioning stage and a fine positioning stage. Based on practical production experience, "step loss" and "overshoot" are the two most common and serious culprits affecting the positioning accuracy of stepper motors during operation.
The main reasons for inaccurate positioning include:
(1) The initial starting speed is too high, exceeding the motor's limit starting frequency, or the acceleration is too large, causing "step loss";
(2) The power of the motor does not meet the system requirements;
(3) The actuator's working process is subject to interference;
(4) The controller of the control system malfunctions;
(5) Pulse loss during reversal; accurate positioning during unidirectional operation; positioning deviation after reversal; and the more reversal is performed, the more obvious the deviation becomes.
(6) The software has design flaws;
(7) When using synchronous belts, the software compensation is too much or too little.
