Motors 2

What are the key operational constraints that must be considered when designing a positioning drive for a stepper motor?

• Low starting pulse rate
• Acceleration must not exceed pull-out torque
• Pulse rate should be lowered before stopping
• All of the above
• None of the above

Answer explanation

Stepper motor operation depends on constraints such as starting pulse rate, acceleration limits, and pulse rate reduction before stopping.

Explain the concept of "ramping" in the context of stepper motor control and why it is necessary.

• Prevents stalling
• Ensures smooth motion
• Reduces sudden torque changes
• All of the above
• None of the above

Answer explanation

Ramping prevents stalling and ensures smooth motion by gradually adjusting the stepping rate.

Describe the difference between Variable Reluctance (VR) and Hybrid stepper motors.

• Uses reluctance torque only
• Uses reluctance torque and permanent magnet
• Suitable for large step angles
• Suitable for small step angles
• Both B and D

Answer explanation

VR motors use reluctance torque alone, while Hybrid motors combine reluctance torque with a permanent magnet for better performance.

What is the significance of the "one-to-one correspondence" between pulses and steps in stepper motors?

• Enables precise position control
• Reduces power consumption
• Increases efficiency
• Only applies to hybrid motors
• None of the above

Answer explanation

Each input pulse results in a precise step, ensuring accurate open-loop position control.

How does load torque affect the accuracy of the step position in a stepper motor?

• Causes step position error
• Improves accuracy
• Reduces current demand
• Increases efficiency
• None of the above

Answer explanation

Load torque introduces step position error, causing angular deviations.

Explain how "half-stepping" increases the resolution and smoothness of the shaft rotation compared to full-stepping.

• Reduces step size
• Improves smoothness
• Alternates between one-phase-on and two-phase-on modes
• All of the above
• None of the above

Answer explanation

Half-stepping reduces step size and increases smoothness by alternating between one-phase-on and two-phase-on modes.

Briefly explain the difference between a constant-voltage and a constant-current drive for a stepper motor.

• Constant voltage has exponential current rise
• Constant current has rectangular current waveforms
• Both A and B
• None
• N/A

Answer explanation

Constant-voltage drives allow exponential current rise, while constant-current drives maintain steady current.

Why is it important to consider the "motor and drive together, as a package" when designing a stepper motor system?

• Ensures compatibility
• Optimizes performance
• Reduces failure rates
• All of the above
• None of the above

Answer explanation

Motor performance depends on drive characteristics, necessitating a combined approach.

What are two distinct mechanisms that cause dips in measured torque-speed curves?

• Resonance
• Instability
• Improper wiring
• Excessive load
• Both A and B

Answer explanation

Resonance and instability contribute to torque dips.

Describe one method used to detect the position of the rotor when trying to eliminate an encoder.

• Measuring winding currents
• Using an optical sensor
• Magnetic field analysis
• All of the above
• None of the above

Answer explanation

Rotor position can be inferred from winding current changes.