1. Why does the stepper motor oscillate?
(1). Oscillation is a general phenomenon that exists when the stepper motor is working, but severe oscillation will cause out-of-step. There are many reasons for oscillation, among which the main reason is that the stepper motor is running at low frequency and single step; the commutation frequency of the stepper motor is equal to the characteristic frequency, double characteristic frequency, and fractional characteristic frequency of the rotor; the stepper motor stops suddenly, etc. .
(2) When the stepper motor rotates in a single step, its working frequency must be in the low frequency range. At the beginning of work, the rotor accelerates under the action of the magnetic field torque. When the rotor turns to a new equilibrium point, its speed is still quite high, thereby overshooting the equilibrium stable point and generating an overshoot. On the one hand, the car overshoots forward. When the rotor speed is reduced to zero, due to the effect of the magnetic field pulling torque, it reverses to the equilibrium point, and reverse overshoot is formed. Due to mechanical friction torque and electromagnetic torque. Form a damping vibration process. Finally, the rotor stops steadily at the equilibrium 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 stepper motor, that is, it is generated below the commutation speed. This is because the electric energy input to the motor is insufficient, and the synchronous torque generated in the stepper motor cannot make the rotor speed follow the rotation speed of the stator magnetic field, thereby causing out-of-step. And any working frequency higher than this frequency will be out of sync. This out-of-step indicates that the stepping motor has insufficient dragging ability. Once the load is reduced, or the excitation 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 the average rotation speed of the stator magnetic field. At this time, the stator is energized and excited for a longer period of time, which is longer than the time required for the rotor to step further, and the rotor obtains too much energy during the stepping process, thereby generating wobble oscillations of forward and backward impact. When the oscillation is severe enough, it will cause out of step.
3. Why does the load capacity of the stepper motor decrease after the frequency increases?
(1) The influence of the stator winding inductance: Because each phase winding of the stepper motor is an inductive coil, it has a certain inductance, and the inductance has the characteristics of delaying the current change. In layman's terms, 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 the time to obtain a higher current. At high frequency, the energizing time and de-energizing time of each phase winding are very short, 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 that the higher the frequency, the smaller the average current in the winding, the average torque of the motor is greatly reduced, and the load capacity is greatly reduced.
(2) When the frequency increases, the eddy current loss in the core of the stepper motor will also increase quickly, 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 stepper motor gradually decreases. After reaching a certain frequency, the stepper motor can no longer carry any load.
