Definition of a stepper motor: Which statement best describes a stepper motor's fundamental operation?
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AA two-phase induction motor used for continuous-speed drives
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BA rotating amplifier that boosts analog signals
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CAn electromagnetic transducer converting shaft angle into an electrical signal
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DAn electromechanical device that executes discrete step angular movements in response to a train of input pulses (one pulse → one step)
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EA servo motor that always rotates synchronously with mains frequency
Answer
Correct Answer: An electromechanical device that executes discrete step angular movements in response to a train of input pulses (one pulse → one step)
Explanation
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:
Apply a pulse to phase A → rotor aligns to position 1.Advance the excitation to phase B → rotor moves one step to position 2.Repeat the sequence to generate a series of precise increments; microstepping subdivides these steps using controlled current waveforms.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).