CRE Power Systems & Actuators 3

Question 1

What phenomenon occurs in a gearbox used with a robotic joint actuator when the output shaft cannot back-drive the input shaft, and why is this property sometimes desired?

Accepted Answer

Self-locking (irreversibility) — desired to hold position without continuous motor torque

Answer

Self-locking gearboxes (common in worm gears) prevent back-driving, allowing a robotic joint to hold its position under load without the motor consuming power, which is useful for energy efficiency and safety during holds.

Question 2

In a robotic power distribution architecture, why is a separate power rail often used for actuators versus logic and control electronics?

Accepted Answer

Motor switching causes current spikes and EMI that can corrupt logic signals and damage sensitive ICs if sharing a rail

Answer

Motor switching generates large current transients and electromagnetic interference; isolating actuator power from logic rails (using separate regulators and bypass capacitors) prevents noise-induced resets or corruption of microcontrollers.

Question 3

What is 'cogging torque' in a permanent magnet motor, and how does it affect robotic joint performance?

Accepted Answer

Torque ripple caused by magnetic attraction between rotor magnets and stator slots — causes unsmooth motion at low speeds

Answer

Cogging torque arises from the rotor's permanent magnets preferring alignment with stator slots, creating periodic torque ripple that causes jerky motion at low speeds and makes precise low-speed control more difficult.

Question 4

Which energy storage technology is most appropriate for a robot that requires very high peak power bursts lasting a fraction of a second, combined with a standard battery for sustained operation?

Accepted Answer

Ultracapacitor (supercapacitor) bank in parallel with the main battery

Answer

Ultracapacitors deliver and absorb very high currents with fast response times, making them ideal for peak power bursting; they complement the battery by handling transients while the battery provides sustained energy.

Question 5

In a hydraulic robot arm, what is the role of a proportional control valve compared to a simple on/off solenoid valve?

Accepted Answer

Proportional valves modulate flow rate continuously in proportion to an input signal, enabling precise position and velocity control

Answer

A proportional valve's opening varies continuously with an analog control signal, allowing smooth modulation of hydraulic flow and therefore precise control of actuator speed and position rather than just on/off states.

CRE - Certified Robotics Engineer Practice Test

CRE - Certified Robotics Engineer Practice Test

CRE Power Systems & Actuators 3