Many step motor users are faced with a question of whether or not to use microstepping in their stepper motor application. Ã¢â‚¬Å“What will it affect and how will I benefit from it?Ã¢â‚¬? one may ask. The answer requires understanding the relationship between step resolution and torque in a comparative analysis. For this analysis, weÃ¢â‚¬â„¢ll look at three of the most often-used step resolutions: full stepping, half stepping, and 64x microstepping.
In order to understand the relationship between microstepping and torque letÃ¢â‚¬â„¢s first take a look at microstepping at a basic level. Typically, step motors move 1.8 degree per full step. Drivers, such as Lin EngineeringÃ¢â‚¬â„¢s R325, are capable of sending different amounts of current to both the A and 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 degree motor at 0.9 degree per pulse. Furthermore, drivers are capable of splitting the current in many different amounts in order to force the motor to step in miniature step angles, even as small as 0.007 degree per step.
When viewing a driverÃ¢â‚¬â„¢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.
The area under the curve on the waveform identifies how much potential output power can be achieved. Thus, overlaying the waveforms shows how much more output power is generated when using different step resolutions. The area under the full step curve is greater than the area under the 64x microstepping curve. Therefore, more output power can be achieved when operating at full step mode versus the 64x microstepping mode.
With this basic knowledge, one might question how much more torque can really be captured by changing step resolutions? In order to do a fair comparison between full step, half step, and 64x microstep, the same amount of power must be used. With certain step resolutions, the input current versus the average output current differs. LetÃ¢â‚¬â„¢s first find out what the differences are, and then identify values for all three step resolutions that will equate to the same amount of output current.
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 driver will actually produce an overall current of 1.4A. If A and B are both energized, or Ã¢â‚¬Å“on,Ã¢â‚¬? together they create the vector sum of 1.41 A.
During half stepping, a motor rated at 1 A/Phase will actually output an average current of 1.2A of current. Fifty percent of the time, the motor will have one phase on, and 50 percent of the time the motor will have two phases on.
Finally, looking at 64x microstepping,