CRE Power Systems & Actuators 1 — Questions and Answers
Question 1: Which type of actuator converts electrical energy into rotational motion using the interaction of magnetic fields and current-carrying conductors?
- Pneumatic cylinder
- DC electric motor (Correct answer)
- Hydraulic piston
- Piezoelectric stack
Correct answer: DC electric motor
A DC electric motor converts electrical energy into rotational mechanical motion through electromagnetic force between the stator's magnetic field and the rotor's current-carrying windings.
Question 2: In a brushless DC (BLDC) motor, what component performs the commutation function that brushes handled in a brushed DC motor?
- Hall effect sensors and electronic speed controller (ESC) (Correct answer)
- Slip rings and carbon contacts
- Mechanical centrifugal switch
- Capacitor bank and relay circuit
Correct answer: Hall effect sensors and electronic speed controller (ESC)
In a BLDC motor, Hall effect sensors detect rotor position and feed data to an ESC, which electronically switches current to the appropriate stator windings for commutation.
Question 3: A robotic joint requires 50 N·m of torque and the selected motor produces 5 N·m. What gear ratio is needed to meet the torque requirement (ignoring efficiency losses)?
- 5:1
- 10:1 (Correct answer)
- 20:1
- 50:1
Correct answer: 10:1
Gear ratio = required torque / motor torque = 50 N·m / 5 N·m = 10:1, meaning the gearbox multiplies torque tenfold while reducing output speed proportionally.
Question 4: Which actuator type is most suitable for high-force, precise linear motion in a clean-room robotic assembly environment where leaks are unacceptable?
- Hydraulic cylinder
- Pneumatic cylinder
- Electric linear actuator (Correct answer)
- Solenoid valve
Correct answer: Electric linear actuator
Electric linear actuators are ideal for clean-room environments because they produce no fluid leaks, offer precise position control, and require no compressors or hydraulic power units.
Question 5: What is back-EMF (back electromotive force) in a DC motor, and what effect does it have on motor current?
- A voltage that aids the supply voltage, increasing current draw
- A voltage generated by the spinning rotor that opposes the supply voltage, reducing current draw (Correct answer)
- Residual charge stored in motor windings after power-off
- Voltage spikes caused by brush arcing that damage motor controllers
Correct answer: A voltage generated by the spinning rotor that opposes the supply voltage, reducing current draw
Back-EMF is generated by the rotating rotor acting as a generator; it opposes the supply voltage and reduces current draw, limiting speed and providing a natural speed-regulation mechanism.
Question 6: In a pneumatic robotic gripper system, what is the primary function of a pressure regulator?
- Convert AC to DC power for the solenoid valves
- Maintain a consistent downstream pressure regardless of supply pressure fluctuations (Correct answer)
- Filter particulates from the compressed air stream
- Convert linear piston motion into rotational output
Correct answer: Maintain a consistent downstream pressure regardless of supply pressure fluctuations
A pressure regulator maintains a set downstream pressure by continuously adjusting an internal valve, ensuring gripper force remains consistent despite fluctuations in the supply air pressure.
Question 7: Which motor parameter directly determines the no-load speed of a DC motor for a given supply voltage?
- Winding resistance (Rw)
- Torque constant (Kt)
- Back-EMF constant (Kv) (Correct answer)
- Rotor inertia (J)
Correct answer: Back-EMF constant (Kv)
The back-EMF constant (Kv), expressed in RPM/V, directly relates supply voltage to no-load speed; at no load, back-EMF approaches supply voltage and speed ≈ Kv × Vsupply.
CRE Power Systems & Actuators 1
Which type of actuator converts electrical energy into rotational motion using the interaction of magnetic fields and current-carrying conductors?