Microstepping theory of stepper motor

A bipolar stepper motor has two windings. The current through each winding is varied in order to rotate the stepper motor. When considering stepper motor drive techniques, a "phase diagram" is a useful visualization tool. The current through one winding Ia is plotted against the current through the other winding Ib. Modes of operation such as full stepping, half stepping, microstepping, and operation at different current limits can be easily visualized on such a diagram. In addition, it is possible to visualize changes in both power consumption and torque as a function of angular position.

Simple stepper motor controllers are only capable of driving a winding with full positive current, no current, or full negative current. Given these available outputs it is only possible to implement full stepping, half stepping, or wave stepping.

Full Wave Stepping

In full stepping operation, the current required in each winding is either -Imax or +Imax. A step sequence of 4 full steps makes up one complete step cycle. Note that these full step positions are the same as the odd numbered positions from the half stepping sequence.

Phase diagram

Timing Diagram

Half-stepping

In a half stepping operation, the current required in each winding is either -Imax, 0, or +Imax. A step sequence of 8 half steps makes up one complete step cycle.

Phase diagram

Timing diagram

Wave Stepping Wave stepping is another method of full stepping, but with reduced power requirements (and corresponding torque output) since only one winding is powered at a time. The current required in each winding is either -Imax, 0 or +Imax. A step sequence of 4 full steps makes up one complete step cycle. Note that these full step positions are the same as the even numbered positions from the half stepping sequence.

Phase diagram

Timing diagram

Microstepping - square path
This method of microstepping provides the highest peak torque if you are limited by available supply voltage.

Phase diagram

Timing diagram

Microstepping - circular path

This method is also referred to as sine cosine microstepping and is usually what people are referring to when they talk about microstepping, though in fact it is only one method.

Phase diagram

Timing diagram