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

Gear backlash — desired to prevent motor overload

Answer

Resonance — desired for energy storage in dynamic movements

Answer

Backlash compensation — desired for improved position accuracy

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

Actuators require AC power while logic circuits use DC

Answer

Logic circuits cannot operate above 5V, while actuators need 24V or higher

Answer

Separate rails are required by all international robotics safety standards

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

Maximum torque before gear teeth skip — limits payload capacity

Answer

Torque required to overcome internal bearing friction — sets minimum operating current

Answer

Torque drop at high RPM due to back-EMF approaching supply voltage — limits top speed

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

Additional LiPo battery cells in parallel

Answer

DC-DC boost converter with larger inductors

Answer

Higher C-rating battery replacing the standard one

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

Proportional valves operate at higher pressures than solenoid valves

Answer

Proportional valves are used only for return-line flow control, not supply-side

Answer

Proportional valves eliminate the need for position feedback sensors

Question 6

What is regenerative braking in an electric robot drive system, and what happens to the recovered energy?

Accepted Answer

A mode where the decelerating motor acts as a generator, converting kinetic energy back to electrical energy that can charge batteries or be shared on the bus

Answer

A braking mode where friction pads slow the motor; heat energy is dissipated

Answer

A control algorithm that pre-charges motor windings before deceleration to reduce stopping time

Answer

An emergency stop mode that disconnects all power and engages mechanical brakes

Question 7

A robotic actuator's motor is overheating during sustained operation. Which thermal management strategy best addresses the root cause without reducing robot performance?

Accepted Answer

Increase gear ratio to achieve the same joint torque with lower motor current, reducing I²R heat generation

Answer

Reduce PWM duty cycle to lower average motor current

Answer

Add a thermal cutoff switch to shut down the motor when it exceeds 80°C

Answer

Replace the motor with an identical unit and accept periodic thermal shutdowns