STEPPER MOTORS are designed to position an output device. Unlike servomotors, these run open loop, meaning they receive nofeedback as to whether the output device has responded as requested. Thus they can get out of phase with the desired program. They will, however, happily sit energized for an indefinite period, holding the output in one position. Their internal construction consists of a number of magnetic strips arranged around the circumference of both the rotor and stator. When energized, the rotor will move one step, to the next magnet, for each pulse received. Thus, these
are intermittent motion devices and do not provide continuous rotary motion like other motors. The number of magnetic strips determines their resolution (typically a few degrees per step). They are relatively small compared to AC/DC motors and have low torque capacity. They are moderately expensive and require special controllers.