Stepper Motor Troubleshooting

1. How to control the direction of stepper motor?

1. Change the directional level signal of control system.
2. Adjust the motor wiring to change direction, and the details are as follows:
   For two-phase stepper motors, only one phase of the motor wires is exchanged to connect the driver, such as exchanging A + and A-.
   For three-phase stepper motor, just exchange the two adjacent phase of the motor wires. For example, as for the three-phase of A, B, C, it can exchange two-phase of A, B.

2. When stepper motor generates vibration and noise, how to do it?
When the stepper motor is running, if there is obvious noise and vibration is caused to the stepper motor, the following steps is helpful to troubleshooting:

1. It really does matter whether the stepper motor is matched with the driver. If not, it may be useless to take following steps such as division, drive current and speed adjustment. It is suggested to buy a set and ensure it is qualified when selecting the stepper motor and driver.
2. Now the stepper motor driver is divided into digital and analog. The noise of the analog stepper motor driver is large while it is basically no for the digital one, generally because one DSP chip is added to the digital driver to optimize the stepper motor drive. Therefore, to ensure the noise and vibration is as small as it is, it is advised to use the digital stepper driver.
3. Correctly adjust the subdivision and current of the stepper motor driver. The larger the subdivision is, the smaller the change amplitude of coil in motor is. That is, the noise is mitigated. As for subdivision, it is advised to set it as 8 and above. Under the circumstance that there is enough torque to drive the load for the stepper motor, it is also necessary to reduce the driver current. The smaller the parameter set, the small the change amplitude of the coil in the motor is.
4. Correctly set the stepper motor’s acceleration and deceleration and highest rotational velocity. It is easy to generate additional noise during the acceleration and deceleration of the stepper motor. The solution is to increase the acceleration and deceleration of the stepper motor appropriately under the circumstance that acceleration and deceleration doesn’t cause losing step.

3. Why the stepper motor doesn’t rotate or move back and forth after it is powered?
If the stepper motor doesn’t rotate sometimes or move back and forth after starting, the following inspection for troubleshooting can be taken into considerations.

1. When selecting the stepper motor, considering whether the working torque is large enough and whether it can drive the load or not. Therefore, it is recommended to select the motor which has 30%-50% larger torque than the actual needs, because the stepper motor cannot rotate under overload, or causing losing step even if it overloads just one second. More seriously, the stalling or repeated and irregular motioning on the spot will be caused.
2. Check whether the input stroke pulse from the upper controller is correct, or whether the input frequency is high and maybe it is filtered by opt coupler.
3. Check whether the start frequency is too high and whether acceleration process is set in the start procedure. It is better to begin accelerating to the set rate from the start frequency regulated for the motor. No matter the acceleration time is very short, or it cannot be stable.
4. When the motor is not fixed, it is normal that such situation like the motor intense resonance may emerge sometimes. Therefore, the motor should be fixed.
5. Considering whether there is lack of phase. If so, the motor will vibrate and won’t rotate normally. As for 2-phase stepper motor, the motor also cannot work normally in case of wrong phase wiring.

4. Why the torque of stepper motor is decreasing with the rise in rotational velocity?
When the stepper motor rotates, the inductance of each phase winding of motor will form a reverse electromotive force. The higher the frequency is, the larger the reverse electromotive force is. Under its role, the phase current of motor is reduced with the increase in frequency rate (or velocity), thus the torque decreases.

5. Why stepper motor can run normally at low velocity, but can’t start at certain higher velocity with some noise of whistler?
There is a technical parameter for the stepper motor: no-load start frequency. That is, the stepper motor can normally start pulse frequency under no-load. If the pulse frequency is higher than the value, the motor cannot normally start, and the stalling or self-locking may occur. Under the circumstance of load, the start frequency shall be lower. The pulse frequency should have acceleration so that the motor rotates at high velocity. That is, the start frequency is low and then rises to the anticipated high frequency according to the acceleration (the motor runs at from low velocity to the higher one).
Except foregoing reasons, the reason for causing some noise of whistler may also be for large load. If the motor rotates at high velocity, the output torque of the motor will decrease. However, if the load requirement cannot be satisfied, stalling of motor will occur and whistler will be changed along with the change in frequency. The solution is to reduce the rotational velocity or replace for the motor with larger torque. Besides, after the motor rotates at high velocity and then stops, the transient whistler will be caused, which is resulted from chopping of phase current. It is only necessary to set the automatic semi-flow on the stepper driver board as effective.

6. How to prevent the power interference of stepper motor?

1. Install power line filter to reduce the contamination of AC power.
2. Reduce the external interference in power line with the shielded line or the interference of power line in external world.
3. Based on the principle of “single-point-earthing”, earth the grounding of power filter and stepper driver PE (the baseboard of driver and chassis should be insulated.), control pulse and direction pulse DIR-outgoing lines of short circuit, motor earthing line, cable protecting cover between driver and motor and shielded wire of driver to the earthing rod on wall of chassis, and good contact should be realized.
4. Lengthen the distance between control line, power line (L and N) and motor drive line (U, V and W) to avoid crossing, e.g. when dealing with the driver installation site of two drivers of the same chassis in the double-shaft system, put the nameplate of one driver forward and that of the other backward, and shorten the leads as far as possible when making structural arrangement.

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