[Ether]

Stepper motors are often operated open-loop with a relative position command (relative to the startup position or some stall position established at startup).

If the stepper motor torque capability substantially exceeds the maximum expected load, it is assumed that the motor will step faithfully when commanded, which eliminates the need for feedback. Of course, if safety is paramount then this type of open-loop control may not be appropriate (for example, if something were to jam and the motor was unable to move the load, the controller would not know).

The control algorithm meters the steps at a rate slow enough that the motor will track faithfully (based on motor torque capability and expected maximum load). The algorithm keeps track of the commanded steps so it knows the position of the motor (relative to the startup position previously mentioned), without the need for a feedback sensor.