How to Use Microstepping to Get More Torque

Many step motor users are faced with a question of whether or not to use microstepping in their stepper motor application. The answer lies in the understanding of the relationship between step resolution and torque in a comparative analysis. This brief analysis touches on the three most common step resolutions: full stepping, half stepping and 64x microstepping.

To gain an understanding of the relationship between microstepping and torque, it's important to understand microstepping at a basic level. Typically, step motors move 1.8° per full step. Drivers, such as Lin Engineering's R325, are capable of sending different amounts of current to both the A and the B phases of a stepper, forcing it to move at various increments. These small increments are called microstepping a motor. For example, setting the driver at half stepping will move a typical 1.8° motor at 0.9° per pulse. Drivers are capable of splitting the current in many different amounts in order to force the motor to step in miniature step angles as small as 0.007° per step.

When viewing a driver's waveform, the different amounts of current the driver provides to the motor phases are visible. Since current is one of the main forms of input power, and power in equals power out, more current going to the motor will produce more output power.

In order to do a fair comparison, knowing the differences and values of each of the three step resolutions is necessary.

FULL STEPPING
During full stepping, both phases are always on, creating a vector sum of 1.4 times more current than the phase currents. For a motor rated at 1 A/Phase, the drive will actually produce an overall current of 1.4A. If A and B are both energized, or "on", together they create the vector sum of 1.41 A.

HALF STEPPING
During half stepping, a motor rated at 1 A/Phase will actually output an average current of 1.2A of current. Half of the time, the motor will have one phase on, and half of the time, the motor will have two phases on.

64X MICROSTEPPING
The average amount of current that the motor will receive when given 1 A/Phase is 1.4A.The vector sum of phase A and phase B, regardless if there are one or two phases on, is always 1.4A.

A STEP IN THE RIGHT DIRECTION
The process of selecting the right torque versus operation tradeoffs can be accomplished with any driver that is capable of the various microstep settings. Some drivers may not necessarily have full step, half step, 4x, 8x, 64x, etc. Smooth motion is so critical with step motors that most newer drivers will have this capability. Since selecting full step verses microstepping is accomplished by initial programming, it is simply a matter of choosing the acceptable performance tradeoffs for the application.