1. Why does the stepping motor oscillate?
(1) Oscillation is a common phenomenon in the operation of stepping motor, but serious oscillation will cause out of step. There are many reasons for the oscillation, among which the main reason is that the stepping motor is in low-frequency single step operation; Commutation frequency of the stepping motor is equal to characteristic frequency, multiple characteristic frequency and fractional characteristic frequency of the rotor; Sudden stop of stepping motor, etc.
(2) When the stepping motor rotates in a single step, its working frequency must be in the low frequency region. At the beginning of operation, the rotor accelerates under the action of magnetic field torque. When the rotor turns to the new balance point, its speed is still quite high, thus overshoot occurs when it crosses the balance stability point. On the one hand, the car overshoot forward. When the rotor speed is reduced to zero, it will reverse towards the balance point due to the effect of the magnetic field pull moment, forming a reverse overshoot. Due to mechanical friction torque and electromagnetic torque. A vibration attenuation process is formed. Finally, the rotor stops stably at the balance point.
2. Why is the stepping motor out of step?
(1) The acceleration of the rotor is slower than the rotating magnetic field of the stepping motor, that is, it is lower than the commutation speed. This is because the power input to the motor is insufficient, and the synchronous torque generated in the stepping motor cannot make the rotor speed follow the rotation speed of the stator magnetic field, resulting in out of step. And any working frequency higher than this frequency will be out of step. This kind of out of step shows that the driving ability of the stepping motor is not enough. Once the load is reduced or the exciting current of the winding is increased, it is possible to overcome the out of step.
(2) The average speed of the rotor is higher than that of the stator magnetic field. At this time, the stator is energized and excited for a long time, which is longer than the time required for the rotor to step further, so the rotor obtains too much energy in the step process, resulting in the oscillation of forward and backward impulses. When the oscillation is serious enough, it will lead to out of step.
3. Why does the load capacity of the stepping motor decrease after the frequency increases?
(1) Influence of stator winding inductance: because each phase winding of stepping motor is an inductance coil, it has certain inductance, and the inductance has the characteristic of delaying the change of current. Generally speaking, when the frequency is low, the power on time and power off time of each phase winding are relatively long, which is greater than the time constant of the coil, and the coil has time to obtain higher current. At high frequency, the power on time and power off time of each phase winding are very short, which is far less than the time constant of the coil, and the current obtained by the coil is very small. The torque is approximately proportional to the square of the current, so the higher the frequency is, the smaller the average current in the winding is, and the average torque and load capacity of the motor are greatly reduced.
(2) When the frequency increases, the eddy current loss in the stepping motor core will also increase rapidly, which is also a factor that reduces the output power and output torque.
(3) Therefore, when the input pulse frequency increases, the load capacity of the stepping motor gradually decreases. After a certain frequency, the stepping motor can not carry any load.
