Position feedback control with a `smart´ controller based on an FPGA

Stepper motors have the advantage of being easily controllable by computer and other digital systems. However, it can be difficult to maintain accurate position control and if one or more steps are missed due to excessive torque, then external sensors are required to detect this. The sensors are available in two forms: absolute and relative. Absolute encoders are preferred as they provide a continuous, accurate measurement of the angle, but they are expensive. Relative encoders rely on periodically obtaining an absolute position measurement, and then using relative measurements from that point to determine the angular position. Even relative optical encoders are fairly expensive. The author describes a new method which uses a technique of relative position measurement but without the need for expensive encoder disks, using a smart controller to maintain a record of the step position