Definition of a stepper motor: Which statement best describes a stepper motor's fundamental operation?

Introduction / Context:
Stepper motors are ubiquitous in motion control for printers, CNC stages, and robotics. Unlike induction or synchronous motors designed for continuous rotation, a stepper moves in discrete angular increments that are commanded digitally.

Given Data / Assumptions:

• Open-loop pulse driving without feedback (typical of basic stepper systems).
• One electrical input pulse corresponds to one mechanical step of fixed angle (e.g., 1.8°).

Concept / Approach:

A stepper motor contains multiple phase windings and a toothed rotor or permanent magnet. Sequencing the phase excitations creates a rotating magnetic field. The rotor aligns successively with each field orientation, producing a train of equal angular steps proportional to the input pulse count.

Step-by-Step Solution:

Verification / Alternative check:

Observe that commanded step count maps directly to shaft position (open-loop), confirming the definition: one pulse produces one step.

Why Other Options Are Wrong:

• Two-phase induction motor is a different machine type relying on slip.
• Rotating amplifier is not a motor.
• An angle transducer that outputs an electrical signal (resolver/encoder) is a sensor, not an actuator.
• A servo that synchronizes to mains frequency describes synchronous motors, not steppers.

Common Pitfalls:

• Confusing stepper motors with servomotors or induction motors.
• Assuming steppers inherently provide feedback; basic systems do not.

Final Answer:

An electromechanical device that executes discrete step angular movements in response to a train of input pulses (one pulse → one step).