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Stepper motor torque becomes smaller as the speed increases
- Oct 09, 2018 -

The stepper motor torque decreases with increasing speed, which is the performance of the stepper motor's torque frequency characteristics.


Characteristics: with the maximum load torque (static torque) as the starting point, with the increase of control pulse frequency, the speed of stepping motor increases gradually, but the load capacity decreases.


The root cause of the decrease in moment frequency characteristics:


1, winding inductance effect:

Both the rise and fall of the current in the winding require a fixed time. When the pulse frequency is low, the period of winding is longer, the average value of the current is larger, the energy obtained by the motor is higher, and the higher torque can be maintained; when the pulse frequency is higher, the period of energization in the winding is shorter. The average  current is small, the motor obtains less energy and the torque decreases.


2. The effect of back EMF resistance:


With the increase of frequency and rotor speed, the additional rotating potential produced in the stator winding makes the motor suffer more damping torque, and the eddy loss of iron core also increases. 


There are two ways to improve the high frequency performance measures of the moment frequency characteristics:


1. Decrease the time constant to increase the resistance. In order to ensure that the current in the energized circuit is constant, the power supply voltage is also increased while increasing the resistance.


2. Improve the working methods. Use multi-phase excitation mode, for example, the four-shot of the two-phase stepping motor changes eight beats. The multi-phase excitation mode can prolong  the time during of each phase, and the motor can obtain more energy and increase the the output torque.

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