When the stepper motor starts and runs, sometimes it stops moving or moves back and forth in place, and sometimes it loses step during operation. What is the problem?

Generally, the following aspects should be considered for inspection:
1) Whether the motor torque is large enough and whether it can drive the load, we generally recommend users to choose a motor with a torque 50% to 100% greater than the actual need when selecting, because stepper motors cannot run under load, even in an instant, it will cause stepping loss, and in severe cases, they may stop or move irregularly in place repeatedly.

2) Is the current of the input step pulse from the upper controller large enough (usually>10mA) to ensure stable conduction of the optocoupler, and is the input frequency too high to receive it? If the output circuit of the upper controller is a CMOS circuit, a CMOS input type driver should also be selected.
3) Is the starting frequency too high and is the acceleration process set in the starting program? It is best to accelerate from the specified starting frequency of the motor to the set frequency, even if the acceleration time is short, otherwise it may be unstable or even in a lazy state.
4) When the motor is not fixed properly, sometimes this situation occurs, which is considered normal. Because, in reality, this caused a strong resonance of the motor, leading to an out of step state. The motor must be securely fixed.
5) For a 5-phase motor, if the phase is connected incorrectly, the motor will not work.