count the steps, divide it by the max resolution of your sensor and then use it to determine the position of the stepper.
it is automated and can adapt to the space and step resolution without changing much, it can be used for an easy camera track, fast tries with robot parts, test an assembly or more complex robots.
might improve in reciving a PWM signal as a servo(independient from the main control board, just using one pin for the signal instead of 3) and use it as one with the adventage of using already owned stepper motors or they cheap price and great quality thanks to 3D Printing
(currently using a freescale microcontroller but it could be adapted to arduino easily)
the idea is to optimize outputs or just use it as a standalone "box" without coding