Stepper motors have a natural tendency to want to move towards their full step ON position. This magnetic pull is called the detent torque of the motor, which causes a jerking motion as the motor nears these positions. In a bipolar stepper motor, one phase will have 100% current and the other phase will have 0% current (this is what we’ll call the zero crossing point). Phases A and B are 90° offset and both have a sinusoidal current waveforms.

Engineers in the Motion Control Industry have gone through the trial and error process, tweaking the current sine waves in order to alleviate the “jerk” that the motor makes as it is forcefully pulled towards the zero crossing spots. However, these zero crossing spots are sensitive to the minimal amount of change so altering the waveform can greatly affect other areas of the driver’s performance.

The R325 Driver and SilverPak 23D Integrated Step Motor + Driver output the right amount of both holding and running current into the motor to overcome the motor’s detent torque. The following graphs use the same step motor to run the step-to-step tests. The R325 and a comparable driver were both set to 64 microstepping, the shaft of the motor was aligned to an encoder which graphed the position of the motor over time.