I am really not sure what the duty cycle needs to be. But the steppers are driving a peristaltic pump for precision metering. The rpm will vary between 3.75 rpm to 325 rpm, with a 50% torque capacity. Is that the same as duty cycle?
Each stepper motor winding is energized one in every four input pulses. Consequently, the pulse train for each winding has a 25 percent duty cycle.