Short note: Stepper motor

A stepper (stepping) motor is a brushless motor whose shaft rotates in discrete angular steps, one step for each input pulse, so position is controlled without feedback (open loop).

Construction and types

• Stator has salient poles with windings grouped into phases, energised in sequence by a digital driver.
• Rotor types: variable reluctance (soft iron, toothed), permanent magnet, and hybrid (PM + toothed).

Working

• When a phase is energised, the rotor turns to the position of minimum reluctance (or aligns its magnet) with that phase.
• Switching the next phase moves the rotor by one step angle:

$$\beta = \frac{360^\circ}{m N_r} \quad (m = \text{phases},\ N_r = \text{rotor teeth})$$

• Speed is proportional to pulse rate; direction depends on the switching sequence.

 pulses --> [Logic/driver] --> phases A,B,C --> motor
             A -> B -> C -> A  : clockwise steps

Advantages and applications

• Precise positioning, no cumulative error, digital compatibility, holding torque at rest.
• Used in printers, plotters, disk drives, CNC machines, robots and camera lenses.