# Subdivision Principle of Stepper Motor Driver

A stepper motor is equipped with a permanent magnet rotor and a stator with at least two windings. When the rotor is magnetically aligned with the stator winding, the second winding will be driven. The two windings turn on and off alternately, which will cause the motor to lock in the desired step position. The direction of current flow through the windings can also be reversed.

In a stepper motor with two stator windings, there are four steps separated by 90°. The subdivision principle of the stepper motor driver is introduced. According to the pulses provided to the stator winding, the stepper movement of the stepper motor can be precisely controlled. The speed control of the stepper motor can be achieved by supplying a pulse frequency to the winding, while the direction of rotation can be changed by reversing the pulse train. The pole pieces inside the motor have many teeth that help locate the rotor relative to the stator. Some stepper motors also have teeth on the stator stages. Depending on the control technology used, stepper motors can be controlled in full, half, or microstepping. Simple square pulses can control motors in full stepping, while advanced control techniques such as pulse width modulation (PWM) can be used for microstepping.

The subdivision is mainly to improve the running performance of the motor. The subdivision control of the stepper servo motor is realized by the driver accurately controlling the phase current of the stepper motor. Taking a two-phase motor as an example, if the rated phase current of the motor is 3A, if Use a conventional driver (such as the common constant current chopper method) to drive the motor. Every time the motor runs, the current in the winding will change from 0 to 3A or from 3A to 0. The huge change in phase current will inevitably cause the motor Vibration and noise of operation. If a subdivided stepper motor driver is used to drive the motor in a state of 10 subdivisions, the current in the windings changes by only 0.3A instead of 3A for each microstep of the motor, and the current changes in a sinusoidal pattern, which greatly increases the The vibration and noise of the motor are improved, so the performance advantage is the real advantage of the subdivision. Since the subdivision driver needs to precisely control the phase current of the motor, the driver must have very high technical requirements and process requirements, and the cost will also be high.

“Smoothing” does not precisely control the phase current of the motor, but only slows down the rate of change of the current, so “smoothing” does not generate microsteps, and subdivided microsteps can be used for precise positioning.

After the phase current of the motor is smoothed, it will cause a decrease in the motor torque, and the subdivision control will not cause a decrease in the motor torque, on the contrary, the torque will increase.